declare Form
display-buffer
display Property
This is the GNU Emacs Lisp Reference Manual corresponding to Emacs version 25.0.95.
Copyright © 1990–1996, 1998–2016 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with the Invariant Sections being “GNU General Public License,” with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual. Buying copies from the FSF supports it in developing GNU and promoting software freedom.”
Appendices
--- The Detailed Node Listing --- ---------------------------------
Here are other nodes that are subnodes of those already listed, mentioned here so you can get to them in one step:
Introduction
Conventions
Format of Descriptions
Lisp Data Types
Programming Types
Character Type
Cons Cell and List Types
String Type
Editing Types
Numbers
Strings and Characters
Lists
Modifying Existing List Structure
Property Lists
Sequences, Arrays, and Vectors
Hash Tables
Symbols
Symbol Properties
Evaluation
Kinds of Forms
Control Structures
Conditionals
Nonlocal Exits
Errors
Variables
Scoping Rules for Variable Bindings
Buffer-Local Variables
Generalized Variables
Functions
Lambda Expressions
Advising Emacs Lisp Functions
Macros
Common Problems Using Macros
Customization Settings
Customization Types
Loading
Byte Compilation
Debugging Lisp Programs
The Lisp Debugger
Edebug
Breaks
The Outside Context
Edebug and Macros
Debugging Invalid Lisp Syntax
Reading and Printing Lisp Objects
Minibuffers
Completion
Command Loop
Defining Commands
Input Events
Reading Input
Keymaps
Menu Keymaps
Defining Menus
Major and Minor Modes
Hooks
Major Modes
Minor Modes
Mode Line Format
Font Lock Mode
Multiline Font Lock Constructs
Automatic Indentation of code
Simple Minded Indentation Engine
Documentation
Files
Visiting Files
Information about Files
File Names
File Format Conversion
Backups and Auto-Saving
Backup Files
Buffers
Windows
Frames
Frame Geometry
Frame Parameters
Window Frame Parameters
Positions
Motion
Markers
Text
The Kill Ring
Indentation
Text Properties
Parsing HTML and XML
Non-ASCII Characters
Coding Systems
Searching and Matching
Regular Expressions
Syntax of Regular Expressions
The Match Data
Syntax Tables
Syntax Descriptors
Parsing Expressions
Abbrevs and Abbrev Expansion
Processes
Receiving Output from Processes
Low-Level Network Access
Packing and Unpacking Byte Arrays
Emacs Display
The Echo Area
Reporting Warnings
Overlays
Faces
Fringes
The display Property
Images
Buttons
Abstract Display
Character Display
Operating System Interface
Starting Up Emacs
Getting Out of Emacs
Terminal Input
Preparing Lisp code for distribution
Tips and Conventions
GNU Emacs Internals
Object Internals
Most of the GNU Emacs text editor is written in the programming language called Emacs Lisp. You can write new code in Emacs Lisp and install it as an extension to the editor. However, Emacs Lisp is more than a mere extension language; it is a full computer programming language in its own right. You can use it as you would any other programming language.
Because Emacs Lisp is designed for use in an editor, it has special features for scanning and parsing text as well as features for handling files, buffers, displays, subprocesses, and so on. Emacs Lisp is closely integrated with the editing facilities; thus, editing commands are functions that can also conveniently be called from Lisp programs, and parameters for customization are ordinary Lisp variables.
This manual attempts to be a full description of Emacs Lisp. For a beginner's introduction to Emacs Lisp, see An Introduction to Emacs Lisp Programming, by Bob Chassell, also published by the Free Software Foundation. This manual presumes considerable familiarity with the use of Emacs for editing; see The GNU Emacs Manual for this basic information.
Generally speaking, the earlier chapters describe features of Emacs Lisp that have counterparts in many programming languages, and later chapters describe features that are peculiar to Emacs Lisp or relate specifically to editing.
This is the GNU Emacs Lisp Reference Manual, corresponding to Emacs version 25.0.95.
This manual has gone through numerous drafts. It is nearly complete but not flawless. There are a few topics that are not covered, either because we consider them secondary (such as most of the individual modes) or because they are yet to be written. Because we are not able to deal with them completely, we have left out several parts intentionally.
The manual should be fully correct in what it does cover, and it is therefore open to criticism on anything it says—from specific examples and descriptive text, to the ordering of chapters and sections. If something is confusing, or you find that you have to look at the sources or experiment to learn something not covered in the manual, then perhaps the manual should be fixed. Please let us know.
As you use this manual, we ask that you send corrections as soon as you find them. If you think of a simple, real life example for a function or group of functions, please make an effort to write it up and send it in. Please reference any comments to the node name and function or variable name, as appropriate. Also state the number of the edition you are criticizing.
Please send comments and corrections using M-x report-emacs-bug.
Lisp (LISt Processing language) was first developed in the late 1950s at the Massachusetts Institute of Technology for research in artificial intelligence. The great power of the Lisp language makes it ideal for other purposes as well, such as writing editing commands.
Dozens of Lisp implementations have been built over the years, each with its own idiosyncrasies. Many of them were inspired by Maclisp, which was written in the 1960s at MIT's Project MAC. Eventually the implementers of the descendants of Maclisp came together and developed a standard for Lisp systems, called Common Lisp. In the meantime, Gerry Sussman and Guy Steele at MIT developed a simplified but very powerful dialect of Lisp, called Scheme.
GNU Emacs Lisp is largely inspired by Maclisp, and a little by Common Lisp. If you know Common Lisp, you will notice many similarities. However, many features of Common Lisp have been omitted or simplified in order to reduce the memory requirements of GNU Emacs. Sometimes the simplifications are so drastic that a Common Lisp user might be very confused. We will occasionally point out how GNU Emacs Lisp differs from Common Lisp. If you don't know Common Lisp, don't worry about it; this manual is self-contained.
A certain amount of Common Lisp emulation is available via the cl-lib library. See Overview.
Emacs Lisp is not at all influenced by Scheme; but the GNU project has an implementation of Scheme, called Guile. We use it in all new GNU software that calls for extensibility.
This section explains the notational conventions that are used in this manual. You may want to skip this section and refer back to it later.
Throughout this manual, the phrases “the Lisp reader” and “the Lisp printer” refer to those routines in Lisp that convert textual representations of Lisp objects into actual Lisp objects, and vice versa. See Printed Representation, for more details. You, the person reading this manual, are thought of as the programmer and are addressed as “you”. The user is the person who uses Lisp programs, including those you write.
Examples of Lisp code are formatted like this: (list 1 2 3).
Names that represent metasyntactic variables, or arguments to a function
being described, are formatted like this: first-number.
nil and t
In Emacs Lisp, the symbol nil has three separate meanings: it
is a symbol with the name `nil'; it is the logical truth value
false; and it is the empty list—the list of zero elements.
When used as a variable, nil always has the value nil.
As far as the Lisp reader is concerned, `()' and `nil' are
identical: they stand for the same object, the symbol nil. The
different ways of writing the symbol are intended entirely for human
readers. After the Lisp reader has read either `()' or `nil',
there is no way to determine which representation was actually written
by the programmer.
In this manual, we write () when we wish to emphasize that it
means the empty list, and we write nil when we wish to emphasize
that it means the truth value false. That is a good convention to use
in Lisp programs also.
(cons 'foo ()) ; Emphasize the empty list (setq foo-flag nil) ; Emphasize the truth value false
In contexts where a truth value is expected, any non-nil value
is considered to be true. However, t is the preferred way
to represent the truth value true. When you need to choose a
value that represents true, and there is no other basis for
choosing, use t. The symbol t always has the value
t.
In Emacs Lisp, nil and t are special symbols that always
evaluate to themselves. This is so that you do not need to quote them
to use them as constants in a program. An attempt to change their
values results in a setting-constant error. See Constant Variables.
Return non-
nilif object is one of the two canonical boolean values:tornil.
A Lisp expression that you can evaluate is called a form. Evaluating a form always produces a result, which is a Lisp object. In the examples in this manual, this is indicated with `=>':
(car '(1 2))
=> 1
You can read this as “(car '(1 2)) evaluates to 1”.
When a form is a macro call, it expands into a new form for Lisp to evaluate. We show the result of the expansion with `==>'. We may or may not show the result of the evaluation of the expanded form.
(third '(a b c))
==> (car (cdr (cdr '(a b c))))
=> c
To help describe one form, we sometimes show another form that produces identical results. The exact equivalence of two forms is indicated with `=='.
(make-sparse-keymap) == (list 'keymap)
Many of the examples in this manual print text when they are
evaluated. If you execute example code in a Lisp Interaction buffer
(such as the buffer *scratch*), the printed text is inserted into
the buffer. If you execute the example by other means (such as by
evaluating the function eval-region), the printed text is
displayed in the echo area.
Examples in this manual indicate printed text with `-|', irrespective of where that text goes. The value returned by evaluating the form follows on a separate line with `=>'.
(progn (prin1 'foo) (princ "\n") (prin1 'bar))
-| foo
-| bar
=> bar
Some examples signal errors. This normally displays an error message in the echo area. We show the error message on a line starting with `error-->'. Note that `error-->' itself does not appear in the echo area.
(+ 23 'x)
error--> Wrong type argument: number-or-marker-p, x
Some examples describe modifications to the contents of a buffer, by showing the before and after versions of the text. These examples show the contents of the buffer in question between two lines of dashes containing the buffer name. In addition, `-!-' indicates the location of point. (The symbol for point, of course, is not part of the text in the buffer; it indicates the place between two characters where point is currently located.)
---------- Buffer: foo ----------
This is the -!-contents of foo.
---------- Buffer: foo ----------
(insert "changed ")
=> nil
---------- Buffer: foo ----------
This is the changed -!-contents of foo.
---------- Buffer: foo ----------
Functions, variables, macros, commands, user options, and special forms are described in this manual in a uniform format. The first line of a description contains the name of the item followed by its arguments, if any. The category—function, variable, or whatever—appears at the beginning of the line. The description follows on succeeding lines, sometimes with examples.
In a function description, the name of the function being described appears first. It is followed on the same line by a list of argument names. These names are also used in the body of the description, to stand for the values of the arguments.
The appearance of the keyword &optional in the argument list
indicates that the subsequent arguments may be omitted (omitted
arguments default to nil). Do not write &optional when
you call the function.
The keyword &rest (which must be followed by a single
argument name) indicates that any number of arguments can follow. The
single argument name following &rest receives, as its
value, a list of all the remaining arguments passed to the function.
Do not write &rest when you call the function.
Here is a description of an imaginary function foo:
The function
foosubtracts integer1 from integer2, then adds all the rest of the arguments to the result. If integer2 is not supplied, then the number 19 is used by default.(foo 1 5 3 9) => 16 (foo 5) => 14More generally,
(foo w x y...) == (+ (- x w) y...)
By convention, any argument whose name contains the name of a type (e.g., integer, integer1 or buffer) is expected to be of that type. A plural of a type (such as buffers) often means a list of objects of that type. An argument named object may be of any type. (For a list of Emacs object types, see Lisp Data Types.) An argument with any other sort of name (e.g., new-file) is specific to the function; if the function has a documentation string, the type of the argument should be described there (see Documentation).
See Lambda Expressions, for a more complete description of
arguments modified by &optional and &rest.
Command, macro, and special form descriptions have the same format, but the word `Function' is replaced by `Command', `Macro', or `Special Form', respectively. Commands are simply functions that may be called interactively; macros process their arguments differently from functions (the arguments are not evaluated), but are presented the same way.
The descriptions of macros and special forms use a more complex notation to specify optional and repeated arguments, because they can break the argument list down into separate arguments in more complicated ways. `[optional-arg]' means that optional-arg is optional and `repeated-args...' stands for zero or more arguments. Parentheses are used when several arguments are grouped into additional levels of list structure. Here is an example:
This imaginary special form implements a loop that executes the body forms and then increments the variable var on each iteration. On the first iteration, the variable has the value from; on subsequent iterations, it is incremented by one (or by inc if that is given). The loop exits before executing body if var equals to. Here is an example:
(count-loop (i 0 10) (prin1 i) (princ " ") (prin1 (aref vector i)) (terpri))If from and to are omitted, var is bound to
nilbefore the loop begins, and the loop exits if var is non-nilat the beginning of an iteration. Here is an example:(count-loop (done) (if (pending) (fixit) (setq done t)))In this special form, the arguments from and to are optional, but must both be present or both absent. If they are present, inc may optionally be specified as well. These arguments are grouped with the argument var into a list, to distinguish them from body, which includes all remaining elements of the form.
A variable is a name that can be bound (or set) to an object. The object to which a variable is bound is called a value; we say also that variable holds that value. Although nearly all variables can be set by the user, certain variables exist specifically so that users can change them; these are called user options. Ordinary variables and user options are described using a format like that for functions, except that there are no arguments.
Here is a description of the imaginary electric-future-map
variable.
The value of this variable is a full keymap used by Electric Command Future mode. The functions in this map allow you to edit commands you have not yet thought about executing.
User option descriptions have the same format, but `Variable' is replaced by `User Option'.
These facilities provide information about which version of Emacs is in use.
This function returns a string describing the version of Emacs that is running. It is useful to include this string in bug reports.
(emacs-version) => "GNU Emacs 24.5.1 (x86_64-unknown-linux-gnu, GTK+ Version 3.16) of 2015-06-01"If here is non-
nil, it inserts the text in the buffer before point, and returnsnil. When this function is called interactively, it prints the same information in the echo area, but giving a prefix argument makes here non-nil.
The value of this variable indicates the time at which Emacs was built. It is a list of four integers, like the value of
current-time(see Time of Day).emacs-build-time => (20614 63694 515336 438000)
The value of this variable is the version of Emacs being run. It is a string such as
"23.1.1". The last number in this string is not really part of the Emacs release version number; it is incremented each time Emacs is built in any given directory. A value with four numeric components, such as"22.0.91.1", indicates an unreleased test version.
The major version number of Emacs, as an integer. For Emacs version 23.1, the value is 23.
The minor version number of Emacs, as an integer. For Emacs version 23.1, the value is 1.
This manual was originally written by Robert Krawitz, Bil Lewis, Dan LaLiberte, Richard M. Stallman and Chris Welty, the volunteers of the GNU manual group, in an effort extending over several years. Robert J. Chassell helped to review and edit the manual, with the support of the Defense Advanced Research Projects Agency, ARPA Order 6082, arranged by Warren A. Hunt, Jr. of Computational Logic, Inc. Additional sections have since been written by Miles Bader, Lars Brinkhoff, Chong Yidong, Kenichi Handa, Lute Kamstra, Juri Linkov, Glenn Morris, Thien-Thi Nguyen, Dan Nicolaescu, Martin Rudalics, Kim F. Storm, Luc Teirlinck, and Eli Zaretskii, and others.
Corrections were supplied by Drew Adams, Juanma Barranquero, Karl Berry, Jim Blandy, Bard Bloom, Stephane Boucher, David Boyes, Alan Carroll, Richard Davis, Lawrence R. Dodd, Peter Doornbosch, David A. Duff, Chris Eich, Beverly Erlebacher, David Eckelkamp, Ralf Fassel, Eirik Fuller, Stephen Gildea, Bob Glickstein, Eric Hanchrow, Jesper Harder, George Hartzell, Nathan Hess, Masayuki Ida, Dan Jacobson, Jak Kirman, Bob Knighten, Frederick M. Korz, Joe Lammens, Glenn M. Lewis, K. Richard Magill, Brian Marick, Roland McGrath, Stefan Monnier, Skip Montanaro, John Gardiner Myers, Thomas A. Peterson, Francesco Potortì, Friedrich Pukelsheim, Arnold D. Robbins, Raul Rockwell, Jason Rumney, Per Starbäck, Shinichirou Sugou, Kimmo Suominen, Edward Tharp, Bill Trost, Rickard Westman, Jean White, Eduard Wiebe, Matthew Wilding, Carl Witty, Dale Worley, Rusty Wright, and David D. Zuhn.
For a more complete list of contributors, please see the relevant change log entries in the Emacs source repository.
A Lisp object is a piece of data used and manipulated by Lisp programs. For our purposes, a type or data type is a set of possible objects.
Every object belongs to at least one type. Objects of the same type have similar structures and may usually be used in the same contexts. Types can overlap, and objects can belong to two or more types. Consequently, we can ask whether an object belongs to a particular type, but not for the type of an object.
A few fundamental object types are built into Emacs. These, from which all other types are constructed, are called primitive types. Each object belongs to one and only one primitive type. These types include integer, float, cons, symbol, string, vector, hash-table, subr, and byte-code function, plus several special types, such as buffer, that are related to editing. (See Editing Types.)
Each primitive type has a corresponding Lisp function that checks whether an object is a member of that type.
Lisp is unlike many other languages in that its objects are self-typing: the primitive type of each object is implicit in the object itself. For example, if an object is a vector, nothing can treat it as a number; Lisp knows it is a vector, not a number.
In most languages, the programmer must declare the data type of each variable, and the type is known by the compiler but not represented in the data. Such type declarations do not exist in Emacs Lisp. A Lisp variable can have any type of value, and it remembers whatever value you store in it, type and all. (Actually, a small number of Emacs Lisp variables can only take on values of a certain type. See Variables with Restricted Values.)
This chapter describes the purpose, printed representation, and read syntax of each of the standard types in GNU Emacs Lisp. Details on how to use these types can be found in later chapters.
The printed representation of an object is the format of the
output generated by the Lisp printer (the function prin1) for
that object. Every data type has a unique printed representation.
The read syntax of an object is the format of the input accepted
by the Lisp reader (the function read) for that object. This
is not necessarily unique; many kinds of object have more than one
syntax. See Read and Print.
In most cases, an object's printed representation is also a read syntax for the object. However, some types have no read syntax, since it does not make sense to enter objects of these types as constants in a Lisp program. These objects are printed in hash notation, which consists of the characters `#<', a descriptive string (typically the type name followed by the name of the object), and a closing `>'. For example:
(current-buffer)
=> #<buffer objects.texi>
Hash notation cannot be read at all, so the Lisp reader signals the
error invalid-read-syntax whenever it encounters `#<'.
In other languages, an expression is text; it has no other form. In
Lisp, an expression is primarily a Lisp object and only secondarily the
text that is the object's read syntax. Often there is no need to
emphasize this distinction, but you must keep it in the back of your
mind, or you will occasionally be very confused.
When you evaluate an expression interactively, the Lisp interpreter
first reads the textual representation of it, producing a Lisp object,
and then evaluates that object (see Evaluation). However,
evaluation and reading are separate activities. Reading returns the
Lisp object represented by the text that is read; the object may or may
not be evaluated later. See Input Functions, for a description of
read, the basic function for reading objects.
A comment is text that is written in a program only for the sake of humans that read the program, and that has no effect on the meaning of the program. In Lisp, a semicolon (`;') starts a comment if it is not within a string or character constant. The comment continues to the end of line. The Lisp reader discards comments; they do not become part of the Lisp objects which represent the program within the Lisp system.
The `#@count' construct, which skips the next count characters, is useful for program-generated comments containing binary data. The Emacs Lisp byte compiler uses this in its output files (see Byte Compilation). It isn't meant for source files, however.
See Comment Tips, for conventions for formatting comments.
There are two general categories of types in Emacs Lisp: those having to do with Lisp programming, and those having to do with editing. The former exist in many Lisp implementations, in one form or another. The latter are unique to Emacs Lisp.
The range of values for an integer depends on the machine. The
minimum range is −536,870,912 to 536,870,911 (30 bits; i.e.,
−2**29
to
2**29 − 1)
but many machines provide a wider range.
Emacs Lisp arithmetic functions do not check for integer overflow. Thus
(1+ 536870911) is −536,870,912 if Emacs integers are 30 bits.
The read syntax for integers is a sequence of (base ten) digits with an optional sign at the beginning and an optional period at the end. The printed representation produced by the Lisp interpreter never has a leading `+' or a final `.'.
-1 ; The integer −1. 1 ; The integer 1. 1. ; Also the integer 1. +1 ; Also the integer 1.
As a special exception, if a sequence of digits specifies an integer
too large or too small to be a valid integer object, the Lisp reader
reads it as a floating-point number (see Floating-Point Type).
For instance, if Emacs integers are 30 bits, 536870912 is read
as the floating-point number 536870912.0.
See Numbers, for more information.
Floating-point numbers are the computer equivalent of scientific
notation; you can think of a floating-point number as a fraction
together with a power of ten. The precise number of significant
figures and the range of possible exponents is machine-specific; Emacs
uses the C data type double to store the value, and internally
this records a power of 2 rather than a power of 10.
The printed representation for floating-point numbers requires either a decimal point (with at least one digit following), an exponent, or both. For example, `1500.0', `+15e2', `15.0e+2', `+1500000e-3', and `.15e4' are five ways of writing a floating-point number whose value is 1500. They are all equivalent.
See Numbers, for more information.
A character in Emacs Lisp is nothing more than an integer. In other words, characters are represented by their character codes. For example, the character A is represented as the integer 65.
Individual characters are used occasionally in programs, but it is more common to work with strings, which are sequences composed of characters. See String Type.
Characters in strings and buffers are currently limited to the range of 0 to 4194303—twenty two bits (see Character Codes). Codes 0 through 127 are ASCII codes; the rest are non-ASCII (see Non-ASCII Characters). Characters that represent keyboard input have a much wider range, to encode modifier keys such as Control, Meta and Shift.
There are special functions for producing a human-readable textual description of a character for the sake of messages. See Describing Characters.
Since characters are really integers, the printed representation of a character is a decimal number. This is also a possible read syntax for a character, but writing characters that way in Lisp programs is not clear programming. You should always use the special read syntax formats that Emacs Lisp provides for characters. These syntax formats start with a question mark.
The usual read syntax for alphanumeric characters is a question mark followed by the character; thus, `?A' for the character A, `?B' for the character B, and `?a' for the character a.
For example:
?Q => 81 ?q => 113
You can use the same syntax for punctuation characters, but it is often a good idea to add a `\' so that the Emacs commands for editing Lisp code don't get confused. For example, `?\(' is the way to write the open-paren character. If the character is `\', you must use a second `\' to quote it: `?\\'.
You can express the characters control-g, backspace, tab, newline, vertical tab, formfeed, space, return, del, and escape as `?\a', `?\b', `?\t', `?\n', `?\v', `?\f', `?\s', `?\r', `?\d', and `?\e', respectively. (`?\s' followed by a dash has a different meaning—it applies the Super modifier to the following character.) Thus,
?\a => 7 ; control-g, C-g ?\b => 8 ; backspace, <BS>, C-h ?\t => 9 ; tab, <TAB>, C-i ?\n => 10 ; newline, C-j ?\v => 11 ; vertical tab, C-k ?\f => 12 ; formfeed character, C-l ?\r => 13 ; carriage return, <RET>, C-m ?\e => 27 ; escape character, <ESC>, C-[ ?\s => 32 ; space character, <SPC> ?\\ => 92 ; backslash character, \ ?\d => 127 ; delete character, <DEL>
These sequences which start with backslash are also known as escape sequences, because backslash plays the role of an escape character; this has nothing to do with the character <ESC>. `\s' is meant for use in character constants; in string constants, just write the space.
A backslash is allowed, and harmless, preceding any character without a special escape meaning; thus, `?\+' is equivalent to `?+'. There is no reason to add a backslash before most characters. However, you should add a backslash before any of the characters `()\|;'`"#.,' to avoid confusing the Emacs commands for editing Lisp code. You can also add a backslash before whitespace characters such as space, tab, newline and formfeed. However, it is cleaner to use one of the easily readable escape sequences, such as `\t' or `\s', instead of an actual whitespace character such as a tab or a space. (If you do write backslash followed by a space, you should write an extra space after the character constant to separate it from the following text.)
In addition to the specific escape sequences for special important control characters, Emacs provides several types of escape syntax that you can use to specify non-ASCII text characters.
Firstly, you can specify characters by their Unicode values.
?\unnnn represents a character with Unicode code point
`U+nnnn', where nnnn is (by convention) a hexadecimal
number with exactly four digits. The backslash indicates that the
subsequent characters form an escape sequence, and the `u'
specifies a Unicode escape sequence.
There is a slightly different syntax for specifying Unicode
characters with code points higher than U+ffff:
?\U00nnnnnn represents the character with code point
`U+nnnnnn', where nnnnnn is a six-digit hexadecimal
number. The Unicode Standard only defines code points up to
`U+10ffff', so if you specify a code point higher than
that, Emacs signals an error.
Secondly, you can specify characters by their hexadecimal character
codes. A hexadecimal escape sequence consists of a backslash,
`x', and the hexadecimal character code. Thus, `?\x41' is
the character A, `?\x1' is the character C-a, and
?\xe0 is the character à (a with grave accent).
You can use any number of hex digits, so you can represent any
character code in this way.
Thirdly, you can specify characters by their character code in
octal. An octal escape sequence consists of a backslash followed by
up to three octal digits; thus, `?\101' for the character
A, `?\001' for the character C-a, and ?\002
for the character C-b. Only characters up to octal code 777 can
be specified this way.
These escape sequences may also be used in strings. See Non-ASCII in Strings.
Control characters can be represented using yet another read syntax. This consists of a question mark followed by a backslash, caret, and the corresponding non-control character, in either upper or lower case. For example, both `?\^I' and `?\^i' are valid read syntax for the character C-i, the character whose value is 9.
Instead of the `^', you can use `C-'; thus, `?\C-i' is equivalent to `?\^I' and to `?\^i':
?\^I => 9 ?\C-I => 9
In strings and buffers, the only control characters allowed are those that exist in ASCII; but for keyboard input purposes, you can turn any character into a control character with `C-'. The character codes for these non-ASCII control characters include the 2**26 bit as well as the code for the corresponding non-control character. Ordinary text terminals have no way of generating non-ASCII control characters, but you can generate them straightforwardly using X and other window systems.
For historical reasons, Emacs treats the <DEL> character as the control equivalent of ?:
?\^? => 127 ?\C-? => 127
As a result, it is currently not possible to represent the character Control-?, which is a meaningful input character under X, using `\C-'. It is not easy to change this, as various Lisp files refer to <DEL> in this way.
For representing control characters to be found in files or strings, we recommend the `^' syntax; for control characters in keyboard input, we prefer the `C-' syntax. Which one you use does not affect the meaning of the program, but may guide the understanding of people who read it.
A meta character is a character typed with the <META> modifier key. The integer that represents such a character has the 2**27 bit set. We use high bits for this and other modifiers to make possible a wide range of basic character codes.
In a string, the 2**7 bit attached to an ASCII character indicates a meta character; thus, the meta characters that can fit in a string have codes in the range from 128 to 255, and are the meta versions of the ordinary ASCII characters. See Strings of Events, for details about <META>-handling in strings.
The read syntax for meta characters uses `\M-'. For example, `?\M-A' stands for M-A. You can use `\M-' together with octal character codes (see below), with `\C-', or with any other syntax for a character. Thus, you can write M-A as `?\M-A', or as `?\M-\101'. Likewise, you can write C-M-b as `?\M-\C-b', `?\C-\M-b', or `?\M-\002'.
The case of a graphic character is indicated by its character code; for example, ASCII distinguishes between the characters `a' and `A'. But ASCII has no way to represent whether a control character is upper case or lower case. Emacs uses the 2**25 bit to indicate that the shift key was used in typing a control character. This distinction is possible only when you use X terminals or other special terminals; ordinary text terminals do not report the distinction. The Lisp syntax for the shift bit is `\S-'; thus, `?\C-\S-o' or `?\C-\S-O' represents the shifted-control-o character.
The X Window System defines three other modifier bits that can be set in a character: hyper, super and alt. The syntaxes for these bits are `\H-', `\s-' and `\A-'. (Case is significant in these prefixes.) Thus, `?\H-\M-\A-x' represents Alt-Hyper-Meta-x. (Note that `\s' with no following `-' represents the space character.) Numerically, the bit values are 2**22 for alt, 2**23 for super and 2**24 for hyper.
A symbol in GNU Emacs Lisp is an object with a name. The symbol name serves as the printed representation of the symbol. In ordinary Lisp use, with one single obarray (see Creating Symbols), a symbol's name is unique—no two symbols have the same name.
A symbol can serve as a variable, as a function name, or to hold a property list. Or it may serve only to be distinct from all other Lisp objects, so that its presence in a data structure may be recognized reliably. In a given context, usually only one of these uses is intended. But you can use one symbol in all of these ways, independently.
A symbol whose name starts with a colon (`:') is called a keyword symbol. These symbols automatically act as constants, and are normally used only by comparing an unknown symbol with a few specific alternatives. See Constant Variables.
A symbol name can contain any characters whatever. Most symbol names are written with letters, digits, and the punctuation characters `-+=*/'. Such names require no special punctuation; the characters of the name suffice as long as the name does not look like a number. (If it does, write a `\' at the beginning of the name to force interpretation as a symbol.) The characters `_~!@$%^&:<>{}?' are less often used but also require no special punctuation. Any other characters may be included in a symbol's name by escaping them with a backslash. In contrast to its use in strings, however, a backslash in the name of a symbol simply quotes the single character that follows the backslash. For example, in a string, `\t' represents a tab character; in the name of a symbol, however, `\t' merely quotes the letter `t'. To have a symbol with a tab character in its name, you must actually use a tab (preceded with a backslash). But it's rare to do such a thing.
Common Lisp note: In Common Lisp, lower case letters are always folded to upper case, unless they are explicitly escaped. In Emacs Lisp, upper case and lower case letters are distinct.
Here are several examples of symbol names. Note that the `+' in the fourth example is escaped to prevent it from being read as a number. This is not necessary in the sixth example because the rest of the name makes it invalid as a number.
foo ; A symbol named `foo'. FOO ; A symbol named `FOO', different from `foo'. 1+ ; A symbol named `1+' ; (not `+1', which is an integer). \+1 ; A symbol named `+1' ; (not a very readable name). \(*\ 1\ 2\) ; A symbol named `(* 1 2)' (a worse name). +-*/_~!@$%^&=:<>{} ; A symbol named `+-*/_~!@$%^&=:<>{}'. ; These characters need not be escaped.
As an exception to the rule that a symbol's name serves as its printed representation, `##' is the printed representation for an interned symbol whose name is an empty string. Furthermore, `#:foo' is the printed representation for an uninterned symbol whose name is foo. (Normally, the Lisp reader interns all symbols; see Creating Symbols.)
A sequence is a Lisp object that represents an ordered set of elements. There are two kinds of sequence in Emacs Lisp: lists and arrays.
Lists are the most commonly-used sequences. A list can hold elements of any type, and its length can be easily changed by adding or removing elements. See the next subsection for more about lists.
Arrays are fixed-length sequences. They are further subdivided into
strings, vectors, char-tables and bool-vectors. Vectors can hold
elements of any type, whereas string elements must be characters, and
bool-vector elements must be t or nil. Char-tables are
like vectors except that they are indexed by any valid character code.
The characters in a string can have text properties like characters in
a buffer (see Text Properties), but vectors do not support text
properties, even when their elements happen to be characters.
Lists, strings and the other array types also share important
similarities. For example, all have a length l, and all have
elements which can be indexed from zero to l minus one. Several
functions, called sequence functions, accept any kind of sequence.
For example, the function length reports the length of any kind
of sequence. See Sequences Arrays Vectors.
It is generally impossible to read the same sequence twice, since
sequences are always created anew upon reading. If you read the read
syntax for a sequence twice, you get two sequences with equal contents.
There is one exception: the empty list () always stands for the
same object, nil.
A cons cell is an object that consists of two slots, called the car slot and the cdr slot. Each slot can hold any Lisp object. We also say that the car of this cons cell is whatever object its car slot currently holds, and likewise for the cdr.
A list is a series of cons cells, linked together so that the
cdr slot of each cons cell holds either the next cons cell or the
empty list. The empty list is actually the symbol nil.
See Lists, for details. Because most cons cells are used as part
of lists, we refer to any structure made out of cons cells as a
list structure.
A note to C programmers: a Lisp list thus works as a linked list built up of cons cells. Because pointers in Lisp are implicit, we do not distinguish between a cons cell slot holding a value versus pointing to the value.
Because cons cells are so central to Lisp, we also have a word for an object which is not a cons cell. These objects are called atoms.
The read syntax and printed representation for lists are identical, and consist of a left parenthesis, an arbitrary number of elements, and a right parenthesis. Here are examples of lists:
(A 2 "A") ; A list of three elements. () ; A list of no elements (the empty list). nil ; A list of no elements (the empty list). ("A ()") ; A list of one element: the string"A ()". (A ()) ; A list of two elements:Aand the empty list. (A nil) ; Equivalent to the previous. ((A B C)) ; A list of one element ; (which is a list of three elements).
Upon reading, each object inside the parentheses becomes an element
of the list. That is, a cons cell is made for each element. The
car slot of the cons cell holds the element, and its cdr
slot refers to the next cons cell of the list, which holds the next
element in the list. The cdr slot of the last cons cell is set to
hold nil.
The names car and cdr derive from the history of Lisp. The
original Lisp implementation ran on an IBM 704 computer which
divided words into two parts, the address and the
decrement; car was an instruction to extract the contents of
the address part of a register, and cdr an instruction to extract
the contents of the decrement. By contrast, cons cells are named
for the function cons that creates them, which in turn was named
for its purpose, the construction of cells.
A list can be illustrated by a diagram in which the cons cells are
shown as pairs of boxes, like dominoes. (The Lisp reader cannot read
such an illustration; unlike the textual notation, which can be
understood by both humans and computers, the box illustrations can be
understood only by humans.) This picture represents the three-element
list (rose violet buttercup):
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
In this diagram, each box represents a slot that can hold or refer to any Lisp object. Each pair of boxes represents a cons cell. Each arrow represents a reference to a Lisp object, either an atom or another cons cell.
In this example, the first box, which holds the car of the first
cons cell, refers to or holds rose (a symbol). The second
box, holding the cdr of the first cons cell, refers to the next
pair of boxes, the second cons cell. The car of the second cons
cell is violet, and its cdr is the third cons cell. The
cdr of the third (and last) cons cell is nil.
Here is another diagram of the same list, (rose violet
buttercup), sketched in a different manner:
--------------- ---------------- -------------------
| car | cdr | | car | cdr | | car | cdr |
| rose | o-------->| violet | o-------->| buttercup | nil |
| | | | | | | | |
--------------- ---------------- -------------------
A list with no elements in it is the empty list; it is identical
to the symbol nil. In other words, nil is both a symbol
and a list.
Here is the list (A ()), or equivalently (A nil),
depicted with boxes and arrows:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> A --> nil
Here is a more complex illustration, showing the three-element list,
((pine needles) oak maple), the first element of which is a
two-element list:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| --> oak --> maple
|
| --- --- --- ---
--> | | |--> | | |--> nil
--- --- --- ---
| |
| |
--> pine --> needles
The same list represented in the second box notation looks like this:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| o | o------->| oak | o------->| maple | nil |
| | | | | | | | | |
-- | --------- -------------- --------------
|
|
| -------------- ----------------
| | car | cdr | | car | cdr |
------>| pine | o------->| needles | nil |
| | | | | |
-------------- ----------------
Dotted pair notation is a general syntax for cons cells that
represents the car and cdr explicitly. In this syntax,
(a . b) stands for a cons cell whose car is
the object a and whose cdr is the object b. Dotted
pair notation is more general than list syntax because the cdr
does not have to be a list. However, it is more cumbersome in cases
where list syntax would work. In dotted pair notation, the list
`(1 2 3)' is written as `(1 . (2 . (3 . nil)))'. For
nil-terminated lists, you can use either notation, but list
notation is usually clearer and more convenient. When printing a
list, the dotted pair notation is only used if the cdr of a cons
cell is not a list.
Here's an example using boxes to illustrate dotted pair notation.
This example shows the pair (rose . violet):
--- ---
| | |--> violet
--- ---
|
|
--> rose
You can combine dotted pair notation with list notation to represent
conveniently a chain of cons cells with a non-nil final cdr.
You write a dot after the last element of the list, followed by the
cdr of the final cons cell. For example, (rose violet
. buttercup) is equivalent to (rose . (violet . buttercup)).
The object looks like this:
--- --- --- ---
| | |--> | | |--> buttercup
--- --- --- ---
| |
| |
--> rose --> violet
The syntax (rose . violet . buttercup) is invalid because
there is nothing that it could mean. If anything, it would say to put
buttercup in the cdr of a cons cell whose cdr is already
used for violet.
The list (rose violet) is equivalent to (rose . (violet)),
and looks like this:
--- --- --- ---
| | |--> | | |--> nil
--- --- --- ---
| |
| |
--> rose --> violet
Similarly, the three-element list (rose violet buttercup)
is equivalent to (rose . (violet . (buttercup))).
It looks like this:
--- --- --- --- --- ---
| | |--> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
--> rose --> violet --> buttercup
An association list or alist is a specially-constructed list whose elements are cons cells. In each element, the car is considered a key, and the cdr is considered an associated value. (In some cases, the associated value is stored in the car of the cdr.) Association lists are often used as stacks, since it is easy to add or remove associations at the front of the list.
For example,
(setq alist-of-colors
'((rose . red) (lily . white) (buttercup . yellow)))
sets the variable alist-of-colors to an alist of three elements. In the
first element, rose is the key and red is the value.
See Association Lists, for a further explanation of alists and for functions that work on alists. See Hash Tables, for another kind of lookup table, which is much faster for handling a large number of keys.
An array is composed of an arbitrary number of slots for holding or referring to other Lisp objects, arranged in a contiguous block of memory. Accessing any element of an array takes approximately the same amount of time. In contrast, accessing an element of a list requires time proportional to the position of the element in the list. (Elements at the end of a list take longer to access than elements at the beginning of a list.)
Emacs defines four types of array: strings, vectors, bool-vectors, and char-tables.
A string is an array of characters and a vector is an array of
arbitrary objects. A bool-vector can hold only t or nil.
These kinds of array may have any length up to the largest integer.
Char-tables are sparse arrays indexed by any valid character code; they
can hold arbitrary objects.
The first element of an array has index zero, the second element has index 1, and so on. This is called zero-origin indexing. For example, an array of four elements has indices 0, 1, 2, and 3. The largest possible index value is one less than the length of the array. Once an array is created, its length is fixed.
All Emacs Lisp arrays are one-dimensional. (Most other programming languages support multidimensional arrays, but they are not essential; you can get the same effect with nested one-dimensional arrays.) Each type of array has its own read syntax; see the following sections for details.
The array type is a subset of the sequence type, and contains the string type, the vector type, the bool-vector type, and the char-table type.
A string is an array of characters. Strings are used for many purposes in Emacs, as can be expected in a text editor; for example, as the names of Lisp symbols, as messages for the user, and to represent text extracted from buffers. Strings in Lisp are constants: evaluation of a string returns the same string.
See Strings and Characters, for functions that operate on strings.
The read syntax for a string is a double-quote, an arbitrary number
of characters, and another double-quote, "like this". To
include a double-quote in a string, precede it with a backslash; thus,
"\"" is a string containing just one double-quote
character. Likewise, you can include a backslash by preceding it with
another backslash, like this: "this \\ is a single embedded
backslash".
The newline character is not special in the read syntax for strings; if you write a new line between the double-quotes, it becomes a character in the string. But an escaped newline—one that is preceded by `\'—does not become part of the string; i.e., the Lisp reader ignores an escaped newline while reading a string. An escaped space `\ ' is likewise ignored.
"It is useful to include newlines
in documentation strings,
but the newline is \
ignored if escaped."
=> "It is useful to include newlines
in documentation strings,
but the newline is ignored if escaped."
There are two text representations for non-ASCII characters in Emacs strings: multibyte and unibyte (see Text Representations). Roughly speaking, unibyte strings store raw bytes, while multibyte strings store human-readable text. Each character in a unibyte string is a byte, i.e., its value is between 0 and 255. By contrast, each character in a multibyte string may have a value between 0 to 4194303 (see Character Type). In both cases, characters above 127 are non-ASCII.
You can include a non-ASCII character in a string constant by writing it literally. If the string constant is read from a multibyte source, such as a multibyte buffer or string, or a file that would be visited as multibyte, then Emacs reads each non-ASCII character as a multibyte character and automatically makes the string a multibyte string. If the string constant is read from a unibyte source, then Emacs reads the non-ASCII character as unibyte, and makes the string unibyte.
Instead of writing a character literally into a multibyte string, you can write it as its character code using an escape sequence. See General Escape Syntax, for details about escape sequences.
If you use any Unicode-style escape sequence `\uNNNN' or `\U00NNNNNN' in a string constant (even for an ASCII character), Emacs automatically assumes that it is multibyte.
You can also use hexadecimal escape sequences (`\xn') and octal escape sequences (`\n') in string constants. But beware: If a string constant contains hexadecimal or octal escape sequences, and these escape sequences all specify unibyte characters (i.e., less than 256), and there are no other literal non-ASCII characters or Unicode-style escape sequences in the string, then Emacs automatically assumes that it is a unibyte string. That is to say, it assumes that all non-ASCII characters occurring in the string are 8-bit raw bytes.
In hexadecimal and octal escape sequences, the escaped character code may contain a variable number of digits, so the first subsequent character which is not a valid hexadecimal or octal digit terminates the escape sequence. If the next character in a string could be interpreted as a hexadecimal or octal digit, write `\ ' (backslash and space) to terminate the escape sequence. For example, `\xe0\ ' represents one character, `a' with grave accent. `\ ' in a string constant is just like backslash-newline; it does not contribute any character to the string, but it does terminate any preceding hex escape.
You can use the same backslash escape-sequences in a string constant
as in character literals (but do not use the question mark that begins a
character constant). For example, you can write a string containing the
nonprinting characters tab and C-a, with commas and spaces between
them, like this: "\t, \C-a". See Character Type, for a
description of the read syntax for characters.
However, not all of the characters you can write with backslash escape-sequences are valid in strings. The only control characters that a string can hold are the ASCII control characters. Strings do not distinguish case in ASCII control characters.
Properly speaking, strings cannot hold meta characters; but when a
string is to be used as a key sequence, there is a special convention
that provides a way to represent meta versions of ASCII
characters in a string. If you use the `\M-' syntax to indicate
a meta character in a string constant, this sets the
2**7
bit of the character in the string. If the string is used in
define-key or lookup-key, this numeric code is translated
into the equivalent meta character. See Character Type.
Strings cannot hold characters that have the hyper, super, or alt modifiers.
A string can hold properties for the characters it contains, in addition to the characters themselves. This enables programs that copy text between strings and buffers to copy the text's properties with no special effort. See Text Properties, for an explanation of what text properties mean. Strings with text properties use a special read and print syntax:
#("characters" property-data...)
where property-data consists of zero or more elements, in groups of three as follows:
beg end plist
The elements beg and end are integers, and together specify a range of indices in the string; plist is the property list for that range. For example,
#("foo bar" 0 3 (face bold) 3 4 nil 4 7 (face italic))
represents a string whose textual contents are `foo bar', in which
the first three characters have a face property with value
bold, and the last three have a face property with value
italic. (The fourth character has no text properties, so its
property list is nil. It is not actually necessary to mention
ranges with nil as the property list, since any characters not
mentioned in any range will default to having no properties.)
A vector is a one-dimensional array of elements of any type. It takes a constant amount of time to access any element of a vector. (In a list, the access time of an element is proportional to the distance of the element from the beginning of the list.)
The printed representation of a vector consists of a left square bracket, the elements, and a right square bracket. This is also the read syntax. Like numbers and strings, vectors are considered constants for evaluation.
[1 "two" (three)] ; A vector of three elements.
=> [1 "two" (three)]
See Vectors, for functions that work with vectors.
A char-table is a one-dimensional array of elements of any type, indexed by character codes. Char-tables have certain extra features to make them more useful for many jobs that involve assigning information to character codes—for example, a char-table can have a parent to inherit from, a default value, and a small number of extra slots to use for special purposes. A char-table can also specify a single value for a whole character set.
The printed representation of a char-table is like a vector except that there is an extra `#^' at the beginning.1
See Char-Tables, for special functions to operate on char-tables. Uses of char-tables include:
A bool-vector is a one-dimensional array whose elements must
be t or nil.
The printed representation of a bool-vector is like a string, except
that it begins with `#&' followed by the length. The string
constant that follows actually specifies the contents of the bool-vector
as a bitmap—each character in the string contains 8 bits, which
specify the next 8 elements of the bool-vector (1 stands for t,
and 0 for nil). The least significant bits of the character
correspond to the lowest indices in the bool-vector.
(make-bool-vector 3 t)
=> #&3"^G"
(make-bool-vector 3 nil)
=> #&3"^@"
These results make sense, because the binary code for `C-g' is 111 and `C-@' is the character with code 0.
If the length is not a multiple of 8, the printed representation shows extra elements, but these extras really make no difference. For instance, in the next example, the two bool-vectors are equal, because only the first 3 bits are used:
(equal #&3"\377" #&3"\007")
=> t
A hash table is a very fast kind of lookup table, somewhat like an alist in that it maps keys to corresponding values, but much faster. The printed representation of a hash table specifies its properties and contents, like this:
(make-hash-table)
=> #s(hash-table size 65 test eql rehash-size 1.5
rehash-threshold 0.8 data ())
See Hash Tables, for more information about hash tables.
Lisp functions are executable code, just like functions in other
programming languages. In Lisp, unlike most languages, functions are
also Lisp objects. A non-compiled function in Lisp is a lambda
expression: that is, a list whose first element is the symbol
lambda (see Lambda Expressions).
In most programming languages, it is impossible to have a function without a name. In Lisp, a function has no intrinsic name. A lambda expression can be called as a function even though it has no name; to emphasize this, we also call it an anonymous function (see Anonymous Functions). A named function in Lisp is just a symbol with a valid function in its function cell (see Defining Functions).
Most of the time, functions are called when their names are written in
Lisp expressions in Lisp programs. However, you can construct or obtain
a function object at run time and then call it with the primitive
functions funcall and apply. See Calling Functions.
A Lisp macro is a user-defined construct that extends the Lisp
language. It is represented as an object much like a function, but with
different argument-passing semantics. A Lisp macro has the form of a
list whose first element is the symbol macro and whose cdr
is a Lisp function object, including the lambda symbol.
Lisp macro objects are usually defined with the built-in
defmacro macro, but any list that begins with macro is a
macro as far as Emacs is concerned. See Macros, for an explanation
of how to write a macro.
Warning: Lisp macros and keyboard macros (see Keyboard Macros) are entirely different things. When we use the word “macro” without qualification, we mean a Lisp macro, not a keyboard macro.
A primitive function is a function callable from Lisp but written in the C programming language. Primitive functions are also called subrs or built-in functions. (The word “subr” is derived from “subroutine”.) Most primitive functions evaluate all their arguments when they are called. A primitive function that does not evaluate all its arguments is called a special form (see Special Forms).
It does not matter to the caller of a function whether the function is primitive. However, this does matter if you try to redefine a primitive with a function written in Lisp. The reason is that the primitive function may be called directly from C code. Calls to the redefined function from Lisp will use the new definition, but calls from C code may still use the built-in definition. Therefore, we discourage redefinition of primitive functions.
The term function refers to all Emacs functions, whether written in Lisp or C. See Function Type, for information about the functions written in Lisp.
Primitive functions have no read syntax and print in hash notation with the name of the subroutine.
(symbol-function 'car) ; Access the function cell ; of the symbol. => #<subr car> (subrp (symbol-function 'car)) ; Is this a primitive function? => t ; Yes.
Byte-code function objects are produced by byte-compiling Lisp code (see Byte Compilation). Internally, a byte-code function object is much like a vector; however, the evaluator handles this data type specially when it appears in a function call. See Byte-Code Objects.
The printed representation and read syntax for a byte-code function object is like that for a vector, with an additional `#' before the opening `['.
An autoload object is a list whose first element is the symbol
autoload. It is stored as the function definition of a symbol,
where it serves as a placeholder for the real definition. The autoload
object says that the real definition is found in a file of Lisp code
that should be loaded when necessary. It contains the name of the file,
plus some other information about the real definition.
After the file has been loaded, the symbol should have a new function definition that is not an autoload object. The new definition is then called as if it had been there to begin with. From the user's point of view, the function call works as expected, using the function definition in the loaded file.
An autoload object is usually created with the function
autoload, which stores the object in the function cell of a
symbol. See Autoload, for more details.
A finalizer object helps Lisp code clean up after objects that are no longer needed. A finalizer holds a Lisp function object. When a finalizer object becomes unreachable after a garbage collection pass, Emacs calls the finalizer's associated function object. When deciding whether a finalizer is reachable, Emacs does not count references from finalizer objects themselves, allowing you to use finalizers without having to worry about accidentally capturing references to finalized objects themselves.
Errors in finalizers are printed to *Messages*. Emacs runs
a given finalizer object's associated function exactly once, even
if that function fails.
Make a finalizer that will run function. function will be called after garbage collection when the returned finalizer object becomes unreachable. If the finalizer object is reachable only through references from finalizer objects, it does not count as reachable for the purpose of deciding whether to run function. function will be run once per finalizer object.
The types in the previous section are used for general programming purposes, and most of them are common to most Lisp dialects. Emacs Lisp provides several additional data types for purposes connected with editing.
A buffer is an object that holds text that can be edited (see Buffers). Most buffers hold the contents of a disk file (see Files) so they can be edited, but some are used for other purposes. Most buffers are also meant to be seen by the user, and therefore displayed, at some time, in a window (see Windows). But a buffer need not be displayed in any window. Each buffer has a designated position called point (see Positions); most editing commands act on the contents of the current buffer in the neighborhood of point. At any time, one buffer is the current buffer.
The contents of a buffer are much like a string, but buffers are not used like strings in Emacs Lisp, and the available operations are different. For example, you can insert text efficiently into an existing buffer, altering the buffer's contents, whereas inserting text into a string requires concatenating substrings, and the result is an entirely new string object.
Many of the standard Emacs functions manipulate or test the characters in the current buffer; a whole chapter in this manual is devoted to describing these functions (see Text).
Several other data structures are associated with each buffer:
The local keymap and variable list contain entries that individually override global bindings or values. These are used to customize the behavior of programs in different buffers, without actually changing the programs.
A buffer may be indirect, which means it shares the text of another buffer, but presents it differently. See Indirect Buffers.
Buffers have no read syntax. They print in hash notation, showing the buffer name.
(current-buffer)
=> #<buffer objects.texi>
A marker denotes a position in a specific buffer. Markers therefore have two components: one for the buffer, and one for the position. Changes in the buffer's text automatically relocate the position value as necessary to ensure that the marker always points between the same two characters in the buffer.
Markers have no read syntax. They print in hash notation, giving the current character position and the name of the buffer.
(point-marker)
=> #<marker at 10779 in objects.texi>
See Markers, for information on how to test, create, copy, and move markers.
A window describes the portion of the terminal screen that Emacs uses to display a buffer. Every window has one associated buffer, whose contents appear in the window. By contrast, a given buffer may appear in one window, no window, or several windows.
Though many windows may exist simultaneously, at any time one window is designated the selected window. This is the window where the cursor is (usually) displayed when Emacs is ready for a command. The selected window usually displays the current buffer (see Current Buffer), but this is not necessarily the case.
Windows are grouped on the screen into frames; each window belongs to one and only one frame. See Frame Type.
Windows have no read syntax. They print in hash notation, giving the window number and the name of the buffer being displayed. The window numbers exist to identify windows uniquely, since the buffer displayed in any given window can change frequently.
(selected-window)
=> #<window 1 on objects.texi>
See Windows, for a description of the functions that work on windows.
A frame is a screen area that contains one or more Emacs windows; we also use the term “frame” to refer to the Lisp object that Emacs uses to refer to the screen area.
Frames have no read syntax. They print in hash notation, giving the frame's title, plus its address in core (useful to identify the frame uniquely).
(selected-frame)
=> #<frame emacs@psilocin.gnu.org 0xdac80>
See Frames, for a description of the functions that work on frames.
A terminal is a device capable of displaying one or more Emacs frames (see Frame Type).
Terminals have no read syntax. They print in hash notation giving the terminal's ordinal number and its TTY device file name.
(get-device-terminal nil)
=> #<terminal 1 on /dev/tty>
A window configuration stores information about the positions, sizes, and contents of the windows in a frame, so you can recreate the same arrangement of windows later.
Window configurations do not have a read syntax; their print syntax looks like `#<window-configuration>'. See Window Configurations, for a description of several functions related to window configurations.
A frame configuration stores information about the positions,
sizes, and contents of the windows in all frames. It is not a
primitive type—it is actually a list whose car is
frame-configuration and whose cdr is an alist. Each alist
element describes one frame, which appears as the car of that
element.
See Frame Configurations, for a description of several functions related to frame configurations.
The word process usually means a running program. Emacs itself runs in a process of this sort. However, in Emacs Lisp, a process is a Lisp object that designates a subprocess created by the Emacs process. Programs such as shells, GDB, ftp, and compilers, running in subprocesses of Emacs, extend the capabilities of Emacs. An Emacs subprocess takes textual input from Emacs and returns textual output to Emacs for further manipulation. Emacs can also send signals to the subprocess.
Process objects have no read syntax. They print in hash notation, giving the name of the process:
(process-list)
=> (#<process shell>)
See Processes, for information about functions that create, delete, return information about, send input or signals to, and receive output from processes.
A stream is an object that can be used as a source or sink for characters—either to supply characters for input or to accept them as output. Many different types can be used this way: markers, buffers, strings, and functions. Most often, input streams (character sources) obtain characters from the keyboard, a buffer, or a file, and output streams (character sinks) send characters to a buffer, such as a *Help* buffer, or to the echo area.
The object nil, in addition to its other meanings, may be used
as a stream. It stands for the value of the variable
standard-input or standard-output. Also, the object
t as a stream specifies input using the minibuffer
(see Minibuffers) or output in the echo area (see The Echo Area).
Streams have no special printed representation or read syntax, and print as whatever primitive type they are.
See Read and Print, for a description of functions related to streams, including parsing and printing functions.
A keymap maps keys typed by the user to commands. This mapping
controls how the user's command input is executed. A keymap is actually
a list whose car is the symbol keymap.
See Keymaps, for information about creating keymaps, handling prefix keys, local as well as global keymaps, and changing key bindings.
An overlay specifies properties that apply to a part of a buffer. Each overlay applies to a specified range of the buffer, and contains a property list (a list whose elements are alternating property names and values). Overlay properties are used to present parts of the buffer temporarily in a different display style. Overlays have no read syntax, and print in hash notation, giving the buffer name and range of positions.
See Overlays, for information on how you can create and use overlays.
A font specifies how to display text on a graphical terminal. There are actually three separate font types—font objects, font specs, and font entities—each of which has slightly different properties. None of them have a read syntax; their print syntax looks like `#<font-object>', `#<font-spec>', and `#<font-entity>' respectively. See Low-Level Font, for a description of these Lisp objects.
To represent shared or circular structures within a complex of Lisp objects, you can use the reader constructs `#n=' and `#n#'.
Use #n= before an object to label it for later reference;
subsequently, you can use #n# to refer the same object in
another place. Here, n is some integer. For example, here is how
to make a list in which the first element recurs as the third element:
(#1=(a) b #1#)
This differs from ordinary syntax such as this
((a) b (a))
which would result in a list whose first and third elements look alike but are not the same Lisp object. This shows the difference:
(prog1 nil
(setq x '(#1=(a) b #1#)))
(eq (nth 0 x) (nth 2 x))
=> t
(setq x '((a) b (a)))
(eq (nth 0 x) (nth 2 x))
=> nil
You can also use the same syntax to make a circular structure, which appears as an element within itself. Here is an example:
#1=(a #1#)
This makes a list whose second element is the list itself. Here's how you can see that it really works:
(prog1 nil
(setq x '#1=(a #1#)))
(eq x (cadr x))
=> t
The Lisp printer can produce this syntax to record circular and shared
structure in a Lisp object, if you bind the variable print-circle
to a non-nil value. See Output Variables.
The Emacs Lisp interpreter itself does not perform type checking on the actual arguments passed to functions when they are called. It could not do so, since function arguments in Lisp do not have declared data types, as they do in other programming languages. It is therefore up to the individual function to test whether each actual argument belongs to a type that the function can use.
All built-in functions do check the types of their actual arguments
when appropriate, and signal a wrong-type-argument error if an
argument is of the wrong type. For example, here is what happens if you
pass an argument to + that it cannot handle:
(+ 2 'a)
error--> Wrong type argument: number-or-marker-p, a
If you want your program to handle different types differently, you must do explicit type checking. The most common way to check the type of an object is to call a type predicate function. Emacs has a type predicate for each type, as well as some predicates for combinations of types.
A type predicate function takes one argument; it returns t if
the argument belongs to the appropriate type, and nil otherwise.
Following a general Lisp convention for predicate functions, most type
predicates' names end with `p'.
Here is an example which uses the predicates listp to check for
a list and symbolp to check for a symbol.
(defun add-on (x)
(cond ((symbolp x)
;; If X is a symbol, put it on LIST.
(setq list (cons x list)))
((listp x)
;; If X is a list, add its elements to LIST.
(setq list (append x list)))
(t
;; We handle only symbols and lists.
(error "Invalid argument %s in add-on" x))))
Here is a table of predefined type predicates, in alphabetical order, with references to further information.
atomarraypbool-vector-pbufferpbyte-code-function-pcase-table-pchar-or-string-pchar-table-pcommandpconspcustom-variable-pfloatpfontpframe-configuration-pframe-live-pframepfunctionphash-table-pinteger-or-marker-pintegerpkeymappkeywordplistpmarkerpwholenumpnlistpnumberpnumber-or-marker-poverlaypprocesspsequencepstringpsubrpsymbolpsyntax-table-pvectorpwindow-configuration-pwindow-live-pwindowpbooleanpstring-or-null-pThe most general way to check the type of an object is to call the
function type-of. Recall that each object belongs to one and
only one primitive type; type-of tells you which one (see Lisp Data Types). But type-of knows nothing about non-primitive
types. In most cases, it is more convenient to use type predicates than
type-of.
This function returns a symbol naming the primitive type of object. The value is one of the symbols
bool-vector,buffer,char-table,compiled-function,cons,finalizer,float,font-entity,font-object,font-spec,frame,hash-table,integer,marker,overlay,process,string,subr,symbol,vector,window, orwindow-configuration.(type-of 1) => integer (type-of 'nil) => symbol (type-of '()) ;()isnil. => symbol (type-of '(x)) => cons
Here we describe functions that test for equality between two objects. Other functions test equality of contents between objects of specific types, e.g., strings. For these predicates, see the appropriate chapter describing the data type.
This function returns
tif object1 and object2 are the same object, andnilotherwise.If object1 and object2 are integers with the same value, they are considered to be the same object (i.e.,
eqreturnst). If object1 and object2 are symbols with the same name, they are normally the same object—but see Creating Symbols for exceptions. For other types (e.g., lists, vectors, strings), two arguments with the same contents or elements are not necessarilyeqto each other: they areeqonly if they are the same object, meaning that a change in the contents of one will be reflected by the same change in the contents of the other.(eq 'foo 'foo) => t (eq 456 456) => t (eq "asdf" "asdf") => nil (eq "" "") => t ;; This exception occurs because Emacs Lisp ;; makes just one multibyte empty string, to save space. (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (setq foo '(1 (2 (3)))) => (1 (2 (3))) (eq foo foo) => t (eq foo '(1 (2 (3)))) => nil (eq [(1 2) 3] [(1 2) 3]) => nil (eq (point-marker) (point-marker)) => nilThe
make-symbolfunction returns an uninterned symbol, distinct from the symbol that is used if you write the name in a Lisp expression. Distinct symbols with the same name are noteq. See Creating Symbols.(eq (make-symbol "foo") 'foo) => nil
This function returns
tif object1 and object2 have equal components, andnilotherwise. Whereaseqtests if its arguments are the same object,equallooks inside nonidentical arguments to see if their elements or contents are the same. So, if two objects areeq, they areequal, but the converse is not always true.(equal 'foo 'foo) => t (equal 456 456) => t (equal "asdf" "asdf") => t (eq "asdf" "asdf") => nil (equal '(1 (2 (3))) '(1 (2 (3)))) => t (eq '(1 (2 (3))) '(1 (2 (3)))) => nil (equal [(1 2) 3] [(1 2) 3]) => t (eq [(1 2) 3] [(1 2) 3]) => nil (equal (point-marker) (point-marker)) => t (eq (point-marker) (point-marker)) => nilComparison of strings is case-sensitive, but does not take account of text properties—it compares only the characters in the strings. See Text Properties. Use
equal-including-propertiesto also compare text properties. For technical reasons, a unibyte string and a multibyte string areequalif and only if they contain the same sequence of character codes and all these codes are either in the range 0 through 127 (ASCII) or 160 through 255 (eight-bit-graphic). (see Text Representations).(equal "asdf" "ASDF") => nilHowever, two distinct buffers are never considered
equal, even if their textual contents are the same.
The test for equality is implemented recursively; for example, given
two cons cells x and y, (equal x y)
returns t if and only if both the expressions below return
t:
(equal (car x) (car y))
(equal (cdr x) (cdr y))
Because of this recursive method, circular lists may therefore cause infinite recursion (leading to an error).
This function behaves like
equalin all cases but also requires that for two strings to be equal, they have the same text properties.(equal "asdf" (propertize "asdf" 'asdf t)) => t (equal-including-properties "asdf" (propertize "asdf" 'asdf t)) => nil
GNU Emacs supports two numeric data types: integers and floating-point numbers. Integers are whole numbers such as −3, 0, 7, 13, and 511. Floating-point numbers are numbers with fractional parts, such as −4.5, 0.0, and 2.71828. They can also be expressed in exponential notation: `1.5e2' is the same as `150.0'; here, `e2' stands for ten to the second power, and that is multiplied by 1.5. Integer computations are exact, though they may overflow. Floating-point computations often involve rounding errors, as the numbers have a fixed amount of precision.
The range of values for an integer depends on the machine. The minimum range is −536,870,912 to 536,870,911 (30 bits; i.e., −2**29 to 2**29 − 1), but many machines provide a wider range. Many examples in this chapter assume the minimum integer width of 30 bits. The Lisp reader reads an integer as a sequence of digits with optional initial sign and optional final period. An integer that is out of the Emacs range is treated as a floating-point number.
1 ; The integer 1. 1. ; The integer 1. +1 ; Also the integer 1. -1 ; The integer −1. 9000000000000000000 ; The floating-point number 9e18. 0 ; The integer 0. -0 ; The integer 0.
The syntax for integers in bases other than 10 uses `#' followed by a letter that specifies the radix: `b' for binary, `o' for octal, `x' for hex, or `radixr' to specify radix radix. Case is not significant for the letter that specifies the radix. Thus, `#binteger' reads integer in binary, and `#radixrinteger' reads integer in radix radix. Allowed values of radix run from 2 to 36. For example:
#b101100 => 44
#o54 => 44
#x2c => 44
#24r1k => 44
To understand how various functions work on integers, especially the bitwise operators (see Bitwise Operations), it is often helpful to view the numbers in their binary form.
In 30-bit binary, the decimal integer 5 looks like this:
0000...000101 (30 bits total)
(The `...' stands for enough bits to fill out a 30-bit word; in this case, `...' stands for twenty 0 bits. Later examples also use the `...' notation to make binary integers easier to read.)
The integer −1 looks like this:
1111...111111 (30 bits total)
−1 is represented as 30 ones. (This is called two's complement notation.)
Subtracting 4 from −1 returns the negative integer −5. In binary, the decimal integer 4 is 100. Consequently, −5 looks like this:
1111...111011 (30 bits total)
In this implementation, the largest 30-bit binary integer is 536,870,911 in decimal. In binary, it looks like this:
0111...111111 (30 bits total)
Since the arithmetic functions do not check whether integers go outside their range, when you add 1 to 536,870,911, the value is the negative integer −536,870,912:
(+ 1 536870911)
=> -536870912
=> 1000...000000 (30 bits total)
Many of the functions described in this chapter accept markers for arguments in place of numbers. (See Markers.) Since the actual arguments to such functions may be either numbers or markers, we often give these arguments the name number-or-marker. When the argument value is a marker, its position value is used and its buffer is ignored.
The value of this variable is the largest integer that Emacs Lisp can handle. Typical values are 2**29 − 1 on 32-bit and 2**61 − 1 on 64-bit platforms.
The value of this variable is the smallest integer that Emacs Lisp can handle. It is negative. Typical values are −2**29 on 32-bit and −2**61 on 64-bit platforms.
In Emacs Lisp, text characters are represented by integers. Any
integer between zero and the value of (max-char), inclusive, is
considered to be valid as a character. See Character Codes.
Floating-point numbers are useful for representing numbers that are
not integral. The range of floating-point numbers is
the same as the range of the C data type double on the machine
you are using. On all computers currently supported by Emacs, this is
double-precision IEEE floating point.
The read syntax for floating-point numbers requires either a decimal point, an exponent, or both. Optional signs (`+' or `-') precede the number and its exponent. For example, `1500.0', `+15e2', `15.0e+2', `+1500000e-3', and `.15e4' are five ways of writing a floating-point number whose value is 1500. They are all equivalent. Like Common Lisp, Emacs Lisp requires at least one digit after any decimal point in a floating-point number; `1500.' is an integer, not a floating-point number.
Emacs Lisp treats -0.0 as numerically equal to ordinary zero
with respect to equal and =. This follows the
IEEE floating-point standard, which says -0.0 and
0.0 are numerically equal even though other operations can
distinguish them.
The IEEE floating-point standard supports positive
infinity and negative infinity as floating-point values. It also
provides for a class of values called NaN, or “not a number”;
numerical functions return such values in cases where there is no
correct answer. For example, (/ 0.0 0.0) returns a NaN.
Although NaN values carry a sign, for practical purposes there is no other
significant difference between different NaN values in Emacs Lisp.
Here are read syntaxes for these special floating-point values:
The following functions are specialized for handling floating-point numbers:
This predicate returns
tif its floating-point argument is a NaN,nilotherwise.
This function returns a cons cell
(s.e), where s and e are respectively the significand and exponent of the floating-point number x.If x is finite, then s is a floating-point number between 0.5 (inclusive) and 1.0 (exclusive), e is an integer, and x = s * 2**e. If x is zero or infinity, then s is the same as x. If x is a NaN, then s is also a NaN. If x is zero, then e is 0.
Given a numeric significand s and an integer exponent e, this function returns the floating point number s * 2**e.
This function copies the sign of x2 to the value of x1, and returns the result. x1 and x2 must be floating point.
This function returns the binary exponent of x. More precisely, the value is the logarithm base 2 of |x|, rounded down to an integer.
(logb 10) => 3 (logb 10.0e20) => 69
The functions in this section test for numbers, or for a specific
type of number. The functions integerp and floatp can
take any type of Lisp object as argument (they would not be of much
use otherwise), but the zerop predicate requires a number as
its argument. See also integer-or-marker-p and
number-or-marker-p, in Predicates on Markers.
This predicate tests whether its argument is floating point and returns
tif so,nilotherwise.
This predicate tests whether its argument is an integer, and returns
tif so,nilotherwise.
This predicate tests whether its argument is a number (either integer or floating point), and returns
tif so,nilotherwise.
This predicate (whose name comes from the phrase “natural number”) tests to see whether its argument is a nonnegative integer, and returns
tif so,nilotherwise. 0 is considered non-negative.
This predicate tests whether its argument is zero, and returns
tif so,nilotherwise. The argument must be a number.
(zerop x)is equivalent to(= x 0).
To test numbers for numerical equality, you should normally use
=, not eq. There can be many distinct floating-point
objects with the same numeric value. If you use eq to
compare them, then you test whether two values are the same
object. By contrast, = compares only the numeric values
of the objects.
In Emacs Lisp, each integer is a unique Lisp object.
Therefore, eq is equivalent to = where integers are
concerned. It is sometimes convenient to use eq for comparing
an unknown value with an integer, because eq does not report an
error if the unknown value is not a number—it accepts arguments of
any type. By contrast, = signals an error if the arguments are
not numbers or markers. However, it is better programming practice to
use = if you can, even for comparing integers.
Sometimes it is useful to compare numbers with equal, which
treats two numbers as equal if they have the same data type (both
integers, or both floating point) and the same value. By contrast,
= can treat an integer and a floating-point number as equal.
See Equality Predicates.
There is another wrinkle: because floating-point arithmetic is not exact, it is often a bad idea to check for equality of floating-point values. Usually it is better to test for approximate equality. Here's a function to do this:
(defvar fuzz-factor 1.0e-6)
(defun approx-equal (x y)
(or (= x y)
(< (/ (abs (- x y))
(max (abs x) (abs y)))
fuzz-factor)))
Common Lisp note: Comparing numbers in Common Lisp always requires
= because Common Lisp implements multi-word integers, and two
distinct integer objects can have the same numeric value. Emacs Lisp
can have just one integer object for any given value because it has a
limited range of integers.
This function tests whether all its arguments are numerically equal, and returns
tif so,nilotherwise.
This function acts like
eqexcept when both arguments are numbers. It compares numbers by type and numeric value, so that(eql 1.0 1)returnsnil, but(eql 1.0 1.0)and(eql 1 1)both returnt.
This function tests whether its arguments are numerically equal, and returns
tif they are not, andnilif they are.
This function tests whether each argument is strictly less than the following argument. It returns
tif so,nilotherwise.
This function tests whether each argument is less than or equal to the following argument. It returns
tif so,nilotherwise.
This function tests whether each argument is strictly greater than the following argument. It returns
tif so,nilotherwise.
This function tests whether each argument is greater than or equal to the following argument. It returns
tif so,nilotherwise.
This function returns the largest of its arguments. If any of the arguments is floating point, the value is returned as floating point, even if it was given as an integer.
(max 20) => 20 (max 1 2.5) => 2.5 (max 1 3 2.5) => 3.0
This function returns the smallest of its arguments. If any of the arguments is floating point, the value is returned as floating point, even if it was given as an integer.
(min -4 1) => -4
To convert an integer to floating point, use the function float.
This returns number converted to floating point. If number is already floating point,
floatreturns it unchanged.
There are four functions to convert floating-point numbers to
integers; they differ in how they round. All accept an argument
number and an optional argument divisor. Both arguments
may be integers or floating-point numbers. divisor may also be
nil. If divisor is nil or omitted, these
functions convert number to an integer, or return it unchanged
if it already is an integer. If divisor is non-nil, they
divide number by divisor and convert the result to an
integer. If divisor is zero (whether integer or
floating point), Emacs signals an arith-error error.
This returns number, converted to an integer by rounding towards zero.
(truncate 1.2) => 1 (truncate 1.7) => 1 (truncate -1.2) => -1 (truncate -1.7) => -1
This returns number, converted to an integer by rounding downward (towards negative infinity).
If divisor is specified, this uses the kind of division operation that corresponds to
mod, rounding downward.(floor 1.2) => 1 (floor 1.7) => 1 (floor -1.2) => -2 (floor -1.7) => -2 (floor 5.99 3) => 1
This returns number, converted to an integer by rounding upward (towards positive infinity).
(ceiling 1.2) => 2 (ceiling 1.7) => 2 (ceiling -1.2) => -1 (ceiling -1.7) => -1
This returns number, converted to an integer by rounding towards the nearest integer. Rounding a value equidistant between two integers returns the even integer.
(round 1.2) => 1 (round 1.7) => 2 (round -1.2) => -1 (round -1.7) => -2
Emacs Lisp provides the traditional four arithmetic operations
(addition, subtraction, multiplication, and division), as well as
remainder and modulus functions, and functions to add or subtract 1.
Except for %, each of these functions accepts both integer and
floating-point arguments, and returns a floating-point number if any
argument is floating point.
Emacs Lisp arithmetic functions do not check for integer overflow.
Thus (1+ 536870911) may evaluate to
−536870912, depending on your hardware.
This function returns number-or-marker plus 1. For example,
(setq foo 4) => 4 (1+ foo) => 5This function is not analogous to the C operator
++—it does not increment a variable. It just computes a sum. Thus, if we continue,foo => 4If you want to increment the variable, you must use
setq, like this:(setq foo (1+ foo)) => 5
This function adds its arguments together. When given no arguments,
+returns 0.(+) => 0 (+ 1) => 1 (+ 1 2 3 4) => 10
The
-function serves two purposes: negation and subtraction. When-has a single argument, the value is the negative of the argument. When there are multiple arguments,-subtracts each of the more-numbers-or-markers from number-or-marker, cumulatively. If there are no arguments, the result is 0.(- 10 1 2 3 4) => 0 (- 10) => -10 (-) => 0
This function multiplies its arguments together, and returns the product. When given no arguments,
*returns 1.(*) => 1 (* 1) => 1 (* 1 2 3 4) => 24
With one or more divisors, this function divides number by each divisor in divisors in turn, and returns the quotient. With no divisors, this function returns 1/number, i.e., the multiplicative inverse of number. Each argument may be a number or a marker.
If all the arguments are integers, the result is an integer, obtained by rounding the quotient towards zero after each division.
(/ 6 2) => 3 (/ 5 2) => 2 (/ 5.0 2) => 2.5 (/ 5 2.0) => 2.5 (/ 5.0 2.0) => 2.5 (/ 4.0) => 0.25 (/ 4) => 0 (/ 25 3 2) => 4 (/ -17 6) => -2If you divide an integer by the integer 0, Emacs signals an
arith-errorerror (see Errors). Floating-point division of a nonzero number by zero yields either positive or negative infinity (see Float Basics).
This function returns the integer remainder after division of dividend by divisor. The arguments must be integers or markers.
For any two integers dividend and divisor,
(+ (% dividend divisor) (* (/ dividend divisor) divisor))always equals dividend if divisor is nonzero.
(% 9 4) => 1 (% -9 4) => -1 (% 9 -4) => 1 (% -9 -4) => -1
This function returns the value of dividend modulo divisor; in other words, the remainder after division of dividend by divisor, but with the same sign as divisor. The arguments must be numbers or markers.
Unlike
%,modpermits floating-point arguments; it rounds the quotient downward (towards minus infinity) to an integer, and uses that quotient to compute the remainder.If divisor is zero,
modsignals anarith-errorerror if both arguments are integers, and returns a NaN otherwise.(mod 9 4) => 1 (mod -9 4) => 3 (mod 9 -4) => -3 (mod -9 -4) => -1 (mod 5.5 2.5) => .5For any two numbers dividend and divisor,
(+ (mod dividend divisor) (* (floor dividend divisor) divisor))always equals dividend, subject to rounding error if either argument is floating point and to an
arith-errorif dividend is an integer and divisor is 0. Forfloor, see Numeric Conversions.
The functions ffloor, fceiling, fround, and
ftruncate take a floating-point argument and return a floating-point
result whose value is a nearby integer. ffloor returns the
nearest integer below; fceiling, the nearest integer above;
ftruncate, the nearest integer in the direction towards zero;
fround, the nearest integer.
This function rounds float to the next lower integral value, and returns that value as a floating-point number.
This function rounds float to the next higher integral value, and returns that value as a floating-point number.
This function rounds float towards zero to an integral value, and returns that value as a floating-point number.
This function rounds float to the nearest integral value, and returns that value as a floating-point number. Rounding a value equidistant between two integers returns the even integer.
In a computer, an integer is represented as a binary number, a sequence of bits (digits which are either zero or one). A bitwise operation acts on the individual bits of such a sequence. For example, shifting moves the whole sequence left or right one or more places, reproducing the same pattern moved over.
The bitwise operations in Emacs Lisp apply only to integers.
lsh, which is an abbreviation for logical shift, shifts the bits in integer1 to the left count places, or to the right if count is negative, bringing zeros into the vacated bits. If count is negative,lshshifts zeros into the leftmost (most-significant) bit, producing a positive result even if integer1 is negative. Contrast this withash, below.Here are two examples of
lsh, shifting a pattern of bits one place to the left. We show only the low-order eight bits of the binary pattern; the rest are all zero.(lsh 5 1) => 10 ;; Decimal 5 becomes decimal 10. 00000101 => 00001010 (lsh 7 1) => 14 ;; Decimal 7 becomes decimal 14. 00000111 => 00001110As the examples illustrate, shifting the pattern of bits one place to the left produces a number that is twice the value of the previous number.
Shifting a pattern of bits two places to the left produces results like this (with 8-bit binary numbers):
(lsh 3 2) => 12 ;; Decimal 3 becomes decimal 12. 00000011 => 00001100On the other hand, shifting one place to the right looks like this:
(lsh 6 -1) => 3 ;; Decimal 6 becomes decimal 3. 00000110 => 00000011 (lsh 5 -1) => 2 ;; Decimal 5 becomes decimal 2. 00000101 => 00000010As the example illustrates, shifting one place to the right divides the value of a positive integer by two, rounding downward.
The function
lsh, like all Emacs Lisp arithmetic functions, does not check for overflow, so shifting left can discard significant bits and change the sign of the number. For example, left shifting 536,870,911 produces −2 in the 30-bit implementation:(lsh 536870911 1) ; left shift => -2In binary, the argument looks like this:
;; Decimal 536,870,911 0111...111111 (30 bits total)which becomes the following when left shifted:
;; Decimal −2 1111...111110 (30 bits total)
ash(arithmetic shift) shifts the bits in integer1 to the left count places, or to the right if count is negative.
ashgives the same results aslshexcept when integer1 and count are both negative. In that case,ashputs ones in the empty bit positions on the left, whilelshputs zeros in those bit positions.Thus, with
ash, shifting the pattern of bits one place to the right looks like this:(ash -6 -1) => -3 ;; Decimal −6 becomes decimal −3. 1111...111010 (30 bits total) => 1111...111101 (30 bits total)In contrast, shifting the pattern of bits one place to the right with
lshlooks like this:(lsh -6 -1) => 536870909 ;; Decimal −6 becomes decimal 536,870,909. 1111...111010 (30 bits total) => 0111...111101 (30 bits total)Here are other examples:
; 30-bit binary values (lsh 5 2) ; 5 = 0000...000101 => 20 ; = 0000...010100 (ash 5 2) => 20 (lsh -5 2) ; -5 = 1111...111011 => -20 ; = 1111...101100 (ash -5 2) => -20 (lsh 5 -2) ; 5 = 0000...000101 => 1 ; = 0000...000001 (ash 5 -2) => 1 (lsh -5 -2) ; -5 = 1111...111011 => 268435454 ; = 0011...111110 (ash -5 -2) ; -5 = 1111...111011 => -2 ; = 1111...111110
This function returns the bitwise AND of the arguments: the nth bit is 1 in the result if, and only if, the nth bit is 1 in all the arguments.
For example, using 4-bit binary numbers, the bitwise AND of 13 and 12 is 12: 1101 combined with 1100 produces 1100. In both the binary numbers, the leftmost two bits are both 1 so the leftmost two bits of the returned value are both 1. However, for the rightmost two bits, each is 0 in at least one of the arguments, so the rightmost two bits of the returned value are both 0.
Therefore,
(logand 13 12) => 12If
logandis not passed any argument, it returns a value of −1. This number is an identity element forlogandbecause its binary representation consists entirely of ones. Iflogandis passed just one argument, it returns that argument.; 30-bit binary values (logand 14 13) ; 14 = 0000...001110 ; 13 = 0000...001101 => 12 ; 12 = 0000...001100 (logand 14 13 4) ; 14 = 0000...001110 ; 13 = 0000...001101 ; 4 = 0000...000100 => 4 ; 4 = 0000...000100 (logand) => -1 ; -1 = 1111...111111
This function returns the bitwise inclusive OR of its arguments: the nth bit is 1 in the result if, and only if, the nth bit is 1 in at least one of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If
logioris passed just one argument, it returns that argument.; 30-bit binary values (logior 12 5) ; 12 = 0000...001100 ; 5 = 0000...000101 => 13 ; 13 = 0000...001101 (logior 12 5 7) ; 12 = 0000...001100 ; 5 = 0000...000101 ; 7 = 0000...000111 => 15 ; 15 = 0000...001111
This function returns the bitwise exclusive OR of its arguments: the nth bit is 1 in the result if, and only if, the nth bit is 1 in an odd number of the arguments. If there are no arguments, the result is 0, which is an identity element for this operation. If
logxoris passed just one argument, it returns that argument.; 30-bit binary values (logxor 12 5) ; 12 = 0000...001100 ; 5 = 0000...000101 => 9 ; 9 = 0000...001001 (logxor 12 5 7) ; 12 = 0000...001100 ; 5 = 0000...000101 ; 7 = 0000...000111 => 14 ; 14 = 0000...001110
This function returns the bitwise complement of its argument: the nth bit is one in the result if, and only if, the nth bit is zero in integer, and vice-versa.
(lognot 5) => -6 ;; 5 = 0000...000101 (30 bits total) ;; becomes ;; -6 = 1111...111010 (30 bits total)
These mathematical functions allow integers as well as floating-point numbers as arguments.
These are the basic trigonometric functions, with argument arg measured in radians.
The value of
(asinarg)is a number between −pi/2 and pi/2 (inclusive) whose sine is arg. If arg is out of range (outside [−1, 1]),asinreturns a NaN.
The value of
(acosarg)is a number between 0 and pi (inclusive) whose cosine is arg. If arg is out of range (outside [−1, 1]),acosreturns a NaN.
The value of
(atany)is a number between −pi/2 and pi/2 (exclusive) whose tangent is y. If the optional second argument x is given, the value of(atan y x)is the angle in radians between the vector[x,y]and theXaxis.
This function returns the logarithm of arg, with base base. If you don't specify base, the natural base e is used. If arg or base is negative,
logreturns a NaN.
This function returns x raised to power y. If both arguments are integers and y is positive, the result is an integer; in this case, overflow causes truncation, so watch out. If x is a finite negative number and y is a finite non-integer,
exptreturns a NaN.
This returns the square root of arg. If arg is finite and less than zero,
sqrtreturns a NaN.
In addition, Emacs defines the following common mathematical constants:
A deterministic computer program cannot generate true random numbers. For most purposes, pseudo-random numbers suffice. A series of pseudo-random numbers is generated in a deterministic fashion. The numbers are not truly random, but they have certain properties that mimic a random series. For example, all possible values occur equally often in a pseudo-random series.
Pseudo-random numbers are generated from a seed value. Starting from
any given seed, the random function always generates the same
sequence of numbers. By default, Emacs initializes the random seed at
startup, in such a way that the sequence of values of random
(with overwhelming likelihood) differs in each Emacs run.
Sometimes you want the random number sequence to be repeatable. For
example, when debugging a program whose behavior depends on the random
number sequence, it is helpful to get the same behavior in each
program run. To make the sequence repeat, execute (random "").
This sets the seed to a constant value for your particular Emacs
executable (though it may differ for other Emacs builds). You can use
other strings to choose various seed values.
This function returns a pseudo-random integer. Repeated calls return a series of pseudo-random integers.
If limit is a positive integer, the value is chosen to be nonnegative and less than limit. Otherwise, the value might be any integer representable in Lisp, i.e., an integer between
most-negative-fixnumandmost-positive-fixnum(see Integer Basics).If limit is
t, it means to choose a new seed as if Emacs were restarting, typically from the system entropy. On systems lacking entropy pools, choose the seed from less-random volatile data such as the current time.If limit is a string, it means to choose a new seed based on the string's contents.
A string in Emacs Lisp is an array that contains an ordered sequence of characters. Strings are used as names of symbols, buffers, and files; to send messages to users; to hold text being copied between buffers; and for many other purposes. Because strings are so important, Emacs Lisp has many functions expressly for manipulating them. Emacs Lisp programs use strings more often than individual characters.
See Strings of Events, for special considerations for strings of keyboard character events.
A character is a Lisp object which represents a single character of text. In Emacs Lisp, characters are simply integers; whether an integer is a character or not is determined only by how it is used. See Character Codes, for details about character representation in Emacs.
A string is a fixed sequence of characters. It is a type of sequence called a array, meaning that its length is fixed and cannot be altered once it is created (see Sequences Arrays Vectors). Unlike in C, Emacs Lisp strings are not terminated by a distinguished character code.
Since strings are arrays, and therefore sequences as well, you can
operate on them with the general array and sequence functions documented
in Sequences Arrays Vectors. For example, you can access or
change individual characters in a string using the functions aref
and aset (see Array Functions). However, note that
length should not be used for computing the width of a
string on display; use string-width (see Size of Displayed Text) instead.
There are two text representations for non-ASCII characters in Emacs strings (and in buffers): unibyte and multibyte. For most Lisp programming, you don't need to be concerned with these two representations. See Text Representations, for details.
Sometimes key sequences are represented as unibyte strings. When a unibyte string is a key sequence, string elements in the range 128 to 255 represent meta characters (which are large integers) rather than character codes in the range 128 to 255. Strings cannot hold characters that have the hyper, super or alt modifiers; they can hold ASCII control characters, but no other control characters. They do not distinguish case in ASCII control characters. If you want to store such characters in a sequence, such as a key sequence, you must use a vector instead of a string. See Character Type, for more information about keyboard input characters.
Strings are useful for holding regular expressions. You can also
match regular expressions against strings with string-match
(see Regexp Search). The functions match-string
(see Simple Match Data) and replace-match (see Replacing Match) are useful for decomposing and modifying strings after
matching regular expressions against them.
Like a buffer, a string can contain text properties for the characters in it, as well as the characters themselves. See Text Properties. All the Lisp primitives that copy text from strings to buffers or other strings also copy the properties of the characters being copied.
See Text, for information about functions that display strings or copy them into buffers. See Character Type, and String Type, for information about the syntax of characters and strings. See Non-ASCII Characters, for functions to convert between text representations and to encode and decode character codes.
For more information about general sequence and array predicates, see Sequences Arrays Vectors, and Arrays.
This function returns
tif object is a string ornil. It returnsnilotherwise.
This function returns
tif object is a string or a character (i.e., an integer),nilotherwise.
The following functions create strings, either from scratch, or by putting strings together, or by taking them apart.
This function returns a string made up of count repetitions of character. If count is negative, an error is signaled.
(make-string 5 ?x) => "xxxxx" (make-string 0 ?x) => ""Other functions to compare with this one include
make-vector(see Vectors) andmake-list(see Building Lists).
This returns a string containing the characters characters.
(string ?a ?b ?c) => "abc"
This function returns a new string which consists of those characters from string in the range from (and including) the character at the index start up to (but excluding) the character at the index end. The first character is at index zero. With one argument, this function just copies string.
(substring "abcdefg" 0 3) => "abc"In the above example, the index for `a' is 0, the index for `b' is 1, and the index for `c' is 2. The index 3—which is the fourth character in the string—marks the character position up to which the substring is copied. Thus, `abc' is copied from the string
"abcdefg".A negative number counts from the end of the string, so that −1 signifies the index of the last character of the string. For example:
(substring "abcdefg" -3 -1) => "ef"In this example, the index for `e' is −3, the index for `f' is −2, and the index for `g' is −1. Therefore, `e' and `f' are included, and `g' is excluded.
When
nilis used for end, it stands for the length of the string. Thus,(substring "abcdefg" -3 nil) => "efg"Omitting the argument end is equivalent to specifying
nil. It follows that(substringstring0)returns a copy of all of string.(substring "abcdefg" 0) => "abcdefg"But we recommend
copy-sequencefor this purpose (see Sequence Functions).If the characters copied from string have text properties, the properties are copied into the new string also. See Text Properties.
substringalso accepts a vector for the first argument. For example:(substring [a b (c) "d"] 1 3) => [b (c)]A
wrong-type-argumenterror is signaled if start is not an integer or if end is neither an integer nornil. Anargs-out-of-rangeerror is signaled if start indicates a character following end, or if either integer is out of range for string.Contrast this function with
buffer-substring(see Buffer Contents), which returns a string containing a portion of the text in the current buffer. The beginning of a string is at index 0, but the beginning of a buffer is at index 1.
This works like
substringbut discards all text properties from the value. Also, start may be omitted ornil, which is equivalent to 0. Thus,(substring-no-propertiesstring)returns a copy of string, with all text properties removed.
This function returns a new string consisting of the characters in the arguments passed to it (along with their text properties, if any). The arguments may be strings, lists of numbers, or vectors of numbers; they are not themselves changed. If
concatreceives no arguments, it returns an empty string.(concat "abc" "-def") => "abc-def" (concat "abc" (list 120 121) [122]) => "abcxyz" ;;nilis an empty sequence. (concat "abc" nil "-def") => "abc-def" (concat "The " "quick brown " "fox.") => "The quick brown fox." (concat) => ""This function always constructs a new string that is not
eqto any existing string, except when the result is the empty string (to save space, Emacs makes only one empty multibyte string).For information about other concatenation functions, see the description of
mapconcatin Mapping Functions,vconcatin Vector Functions, andappendin Building Lists. For concatenating individual command-line arguments into a string to be used as a shell command, see combine-and-quote-strings.
This function splits string into substrings based on the regular expression separators (see Regular Expressions). Each match for separators defines a splitting point; the substrings between splitting points are made into a list, which is returned.
If omit-nulls is
nil(or omitted), the result contains null strings whenever there are two consecutive matches for separators, or a match is adjacent to the beginning or end of string. If omit-nulls ist, these null strings are omitted from the result.If separators is
nil(or omitted), the default is the value ofsplit-string-default-separators.As a special case, when separators is
nil(or omitted), null strings are always omitted from the result. Thus:(split-string " two words ") => ("two" "words")The result is not
("" "two" "words" ""), which would rarely be useful. If you need such a result, use an explicit value for separators:(split-string " two words " split-string-default-separators) => ("" "two" "words" "")More examples:
(split-string "Soup is good food" "o") => ("S" "up is g" "" "d f" "" "d") (split-string "Soup is good food" "o" t) => ("S" "up is g" "d f" "d") (split-string "Soup is good food" "o+") => ("S" "up is g" "d f" "d")Empty matches do count, except that
split-stringwill not look for a final empty match when it already reached the end of the string using a non-empty match or when string is empty:(split-string "aooob" "o*") => ("" "a" "" "b" "") (split-string "ooaboo" "o*") => ("" "" "a" "b" "") (split-string "" "") => ("")However, when separators can match the empty string, omit-nulls is usually
t, so that the subtleties in the three previous examples are rarely relevant:(split-string "Soup is good food" "o*" t) => ("S" "u" "p" " " "i" "s" " " "g" "d" " " "f" "d") (split-string "Nice doggy!" "" t) => ("N" "i" "c" "e" " " "d" "o" "g" "g" "y" "!") (split-string "" "" t) => nilSomewhat odd, but predictable, behavior can occur for certain “non-greedy” values of separators that can prefer empty matches over non-empty matches. Again, such values rarely occur in practice:
(split-string "ooo" "o*" t) => nil (split-string "ooo" "\\|o+" t) => ("o" "o" "o")If the optional argument trim is non-
nil, it should be a regular expression to match text to trim from the beginning and end of each substring. If trimming makes the substring empty, it is treated as null.If you need to split a string into a list of individual command-line arguments suitable for
call-processorstart-process, see split-string-and-unquote.
The default value of separators for
split-string. Its usual value is"[ \f\t\n\r\v]+".
The most basic way to alter the contents of an existing string is with
aset (see Array Functions). (aset string
idx char) stores char into string at index
idx. Each character occupies one or more bytes, and if char
needs a different number of bytes from the character already present at
that index, aset signals an error.
A more powerful function is store-substring:
This function alters part of the contents of the string string, by storing obj starting at index idx. The argument obj may be either a character or a (smaller) string.
Since it is impossible to change the length of an existing string, it is an error if obj doesn't fit within string's actual length, or if any new character requires a different number of bytes from the character currently present at that point in string.
To clear out a string that contained a password, use
clear-string:
This makes string a unibyte string and clears its contents to zeros. It may also change string's length.
This function returns
tif the arguments represent the same character,nilotherwise. This function ignores differences in case ifcase-fold-searchis non-nil.(char-equal ?x ?x) => t (let ((case-fold-search nil)) (char-equal ?x ?X)) => nil
This function returns
tif the characters of the two strings match exactly. Symbols are also allowed as arguments, in which case the symbol names are used. Case is always significant, regardless ofcase-fold-search.This function is equivalent to
equalfor comparing two strings (see Equality Predicates). In particular, the text properties of the two strings are ignored; useequal-including-propertiesif you need to distinguish between strings that differ only in their text properties. However, unlikeequal, if either argument is not a string or symbol,string=signals an error.(string= "abc" "abc") => t (string= "abc" "ABC") => nil (string= "ab" "ABC") => nilFor technical reasons, a unibyte and a multibyte string are
equalif and only if they contain the same sequence of character codes and all these codes are either in the range 0 through 127 (ASCII) or 160 through 255 (eight-bit-graphic). However, when a unibyte string is converted to a multibyte string, all characters with codes in the range 160 through 255 are converted to characters with higher codes, whereas ASCII characters remain unchanged. Thus, a unibyte string and its conversion to multibyte are onlyequalif the string is all ASCII. Character codes 160 through 255 are not entirely proper in multibyte text, even though they can occur. As a consequence, the situation where a unibyte and a multibyte string areequalwithout both being all ASCII is a technical oddity that very few Emacs Lisp programmers ever get confronted with. See Text Representations.
This function returns
tif string1 and string2 are equal with respect to collation rules. A collation rule is not only determined by the lexicographic order of the characters contained in string1 and string2, but also further rules about relations between these characters. Usually, it is defined by the locale environment Emacs is running with.For example, characters with different coding points but the same meaning might be considered as equal, like different grave accent Unicode characters:
(string-collate-equalp (string ?\uFF40) (string ?\u1FEF)) => tThe optional argument locale, a string, overrides the setting of your current locale identifier for collation. The value is system dependent; a locale
"en_US.UTF-8"is applicable on POSIX systems, while it would be, e.g.,"enu_USA.1252"on MS-Windows systems.If ignore-case is non-
nil, characters are converted to lower-case before comparing them.To emulate Unicode-compliant collation on MS-Windows systems, bind
w32-collate-ignore-punctuationto a non-nilvalue, since the codeset part of the locale cannot be"UTF-8"on MS-Windows.If your system does not support a locale environment, this function behaves like
string-equal.Do not use this function to compare file names for equality, only for sorting them.
This function returns non-
nilif string1 is a prefix of string2; i.e., if string2 starts with string1. If the optional argument ignore-case is non-nil, the comparison ignores case differences.
This function returns non-
nilif suffix is a suffix of string; i.e., if string ends with suffix. If the optional argument ignore-case is non-nil, the comparison ignores case differences.
This function compares two strings a character at a time. It scans both the strings at the same time to find the first pair of corresponding characters that do not match. If the lesser character of these two is the character from string1, then string1 is less, and this function returns
t. If the lesser character is the one from string2, then string1 is greater, and this function returnsnil. If the two strings match entirely, the value isnil.Pairs of characters are compared according to their character codes. Keep in mind that lower case letters have higher numeric values in the ASCII character set than their upper case counterparts; digits and many punctuation characters have a lower numeric value than upper case letters. An ASCII character is less than any non-ASCII character; a unibyte non-ASCII character is always less than any multibyte non-ASCII character (see Text Representations).
(string< "abc" "abd") => t (string< "abd" "abc") => nil (string< "123" "abc") => tWhen the strings have different lengths, and they match up to the length of string1, then the result is
t. If they match up to the length of string2, the result isnil. A string of no characters is less than any other string.(string< "" "abc") => t (string< "ab" "abc") => t (string< "abc" "") => nil (string< "abc" "ab") => nil (string< "" "") => nilSymbols are also allowed as arguments, in which case their print names are compared.
This function returns the result of comparing string1 and string2 in the opposite order, i.e., it is equivalent to calling
(string-lesspstring2 string1).
This function returns
tif string1 is less than string2 in collation order. A collation order is not only determined by the lexicographic order of the characters contained in string1 and string2, but also further rules about relations between these characters. Usually, it is defined by the locale environment Emacs is running with.For example, punctuation and whitespace characters might be ignored for sorting (see Sequence Functions):
(sort '("11" "12" "1 1" "1 2" "1.1" "1.2") 'string-collate-lessp) => ("11" "1 1" "1.1" "12" "1 2" "1.2")This behavior is system-dependent; e.g., punctuation and whitespace are never ignored on Cygwin, regardless of locale.
The optional argument locale, a string, overrides the setting of your current locale identifier for collation. The value is system dependent; a locale
"en_US.UTF-8"is applicable on POSIX systems, while it would be, e.g.,"enu_USA.1252"on MS-Windows systems. The locale value of"POSIX"or"C"letsstring-collate-lesspbehave likestring-lessp:(sort '("11" "12" "1 1" "1 2" "1.1" "1.2") (lambda (s1 s2) (string-collate-lessp s1 s2 "POSIX"))) => ("1 1" "1 2" "1.1" "1.2" "11" "12")If ignore-case is non-
nil, characters are converted to lower-case before comparing them.To emulate Unicode-compliant collation on MS-Windows systems, bind
w32-collate-ignore-punctuationto a non-nilvalue, since the codeset part of the locale cannot be"UTF-8"on MS-Windows.If your system does not support a locale environment, this function behaves like
string-lessp.
This function returns non-
nilif string1 is a prefix of string2; i.e., if string2 starts with string1. If the optional argument ignore-case is non-nil, the comparison ignores case differences.
This function returns non-
nilif suffix is a suffix of string; i.e., if string ends with suffix. If the optional argument ignore-case is non-nil, the comparison ignores case differences.
This function compares a specified part of string1 with a specified part of string2. The specified part of string1 runs from index start1 (inclusive) up to index end1 (exclusive);
nilfor start1 means the start of the string, whilenilfor end1 means the length of the string. Likewise, the specified part of string2 runs from index start2 up to index end2.The strings are compared by the numeric values of their characters. For instance, str1 is considered less than str2 if its first differing character has a smaller numeric value. If ignore-case is non-
nil, characters are converted to lower-case before comparing them. Unibyte strings are converted to multibyte for comparison (see Text Representations), so that a unibyte string and its conversion to multibyte are always regarded as equal.If the specified portions of the two strings match, the value is
t. Otherwise, the value is an integer which indicates how many leading characters agree, and which string is less. Its absolute value is one plus the number of characters that agree at the beginning of the two strings. The sign is negative if string1 (or its specified portion) is less.
This function works like
assoc, except that key must be a string or symbol, and comparison is done usingcompare-strings. Symbols are converted to strings before testing. If case-fold is non-nil, it ignores case differences. Unlikeassoc, this function can also match elements of the alist that are strings or symbols rather than conses. In particular, alist can be a list of strings or symbols rather than an actual alist. See Association Lists.
See also the function compare-buffer-substrings in
Comparing Text, for a way to compare text in buffers. The
function string-match, which matches a regular expression
against a string, can be used for a kind of string comparison; see
Regexp Search.
This section describes functions for converting between characters,
strings and integers. format (see Formatting Strings) and
prin1-to-string (see Output Functions) can also convert
Lisp objects into strings. read-from-string (see Input Functions) can convert a string representation of a Lisp object
into an object. The functions string-to-multibyte and
string-to-unibyte convert the text representation of a string
(see Converting Representations).
See Documentation, for functions that produce textual descriptions
of text characters and general input events
(single-key-description and text-char-description). These
are used primarily for making help messages.
This function returns a string consisting of the printed base-ten representation of number. The returned value starts with a minus sign if the argument is negative.
(number-to-string 256) => "256" (number-to-string -23) => "-23" (number-to-string -23.5) => "-23.5"
int-to-stringis a semi-obsolete alias for this function.See also the function
formatin Formatting Strings.
This function returns the numeric value of the characters in string. If base is non-
nil, it must be an integer between 2 and 16 (inclusive), and integers are converted in that base. If base isnil, then base ten is used. Floating-point conversion only works in base ten; we have not implemented other radices for floating-point numbers, because that would be much more work and does not seem useful. If string looks like an integer but its value is too large to fit into a Lisp integer,string-to-numberreturns a floating-point result.The parsing skips spaces and tabs at the beginning of string, then reads as much of string as it can interpret as a number in the given base. (On some systems it ignores other whitespace at the beginning, not just spaces and tabs.) If string cannot be interpreted as a number, this function returns 0.
(string-to-number "256") => 256 (string-to-number "25 is a perfect square.") => 25 (string-to-number "X256") => 0 (string-to-number "-4.5") => -4.5 (string-to-number "1e5") => 100000.0
This function returns a new string containing one character, character. This function is semi-obsolete because the function
stringis more general. See Creating Strings.
This function returns the first character in string. This mostly identical to
(aref string 0), except that it returns 0 if the string is empty. (The value is also 0 when the first character of string is the null character, ASCII code 0.) This function may be eliminated in the future if it does not seem useful enough to retain.
Here are some other functions that can convert to or from a string:
concatvconcatappendbyte-to-stringFormatting means constructing a string by substituting computed values at various places in a constant string. This constant string controls how the other values are printed, as well as where they appear; it is called a format string.
Formatting is often useful for computing messages to be displayed. In
fact, the functions message and error provide the same
formatting feature described here; they differ from format-message only
in how they use the result of formatting.
This function returns a new string that is made by copying string and then replacing any format specification in the copy with encodings of the corresponding objects. The arguments objects are the computed values to be formatted.
The characters in string, other than the format specifications, are copied directly into the output, including their text properties, if any.
This function acts like
format, except it also converts any curved single quotes in string as per the value oftext-quoting-style, and treats grave accent (`) and apostrophe (') as if they were curved single quotes.A format that quotes with grave accents and apostrophes `like this' typically generates curved quotes ‘like this’. In contrast, a format that quotes with only apostrophes 'like this' typically generates two closing curved quotes ’like this’, an unusual style in English. See Keys in Documentation, for how the
text-quoting-stylevariable affects generated quotes.
A format specification is a sequence of characters beginning with a
`%'. Thus, if there is a `%d' in string, the
format function replaces it with the printed representation of
one of the values to be formatted (one of the arguments objects).
For example:
(format "The value of fill-column is %d." fill-column)
=> "The value of fill-column is 72."
Since format interprets `%' characters as format
specifications, you should never pass an arbitrary string as
the first argument. This is particularly true when the string is
generated by some Lisp code. Unless the string is known to
never include any `%' characters, pass "%s", described
below, as the first argument, and the string as the second, like this:
(format "%s" arbitrary-string)
If string contains more than one format specification, the format specifications correspond to successive values from objects. Thus, the first format specification in string uses the first such value, the second format specification uses the second such value, and so on. Any extra format specifications (those for which there are no corresponding values) cause an error. Any extra values to be formatted are ignored.
Certain format specifications require values of particular types. If you supply a value that doesn't fit the requirements, an error is signaled.
Here is a table of valid format specifications:
princ, not
prin1—see Output Functions). Thus, strings are represented
by their contents alone, with no `"' characters, and symbols appear
without `\' characters.
If the object is a string, its text properties are
copied into the output. The text properties of the `%s' itself
are also copied, but those of the object take priority.
prin1—see Output Functions). Thus, strings are enclosed in `"' characters, and
`\' characters appear where necessary before special characters.
(format "%% %d" 30) returns "% 30".
Any other format character results in an `Invalid format operation' error.
Here are several examples, which assume the typical
text-quoting-style settings:
(format "The octal value of %d is %o,
and the hex value is %x." 18 18 18)
=> "The octal value of 18 is 22,
and the hex value is 12."
(format-message
"The name of this buffer is ‘%s’." (buffer-name))
=> "The name of this buffer is ‘strings.texi’."
(format-message
"The buffer object prints as `%s'." (current-buffer))
=> "The buffer object prints as ‘strings.texi’."
A specification can have a width, which is a decimal number
between the `%' and the specification character. If the printed
representation of the object contains fewer characters than this
width, format extends it with padding. The width specifier is
ignored for the `%%' specification. Any padding introduced by
the width specifier normally consists of spaces inserted on the left:
(format "%5d is padded on the left with spaces" 123)
=> " 123 is padded on the left with spaces"
If the width is too small, format does not truncate the
object's printed representation. Thus, you can use a width to specify
a minimum spacing between columns with no risk of losing information.
In the following two examples, `%7s' specifies a minimum width
of 7. In the first case, the string inserted in place of `%7s'
has only 3 letters, and needs 4 blank spaces as padding. In the
second case, the string "specification" is 13 letters wide but
is not truncated.
(format "The word '%7s' has %d letters in it."
"foo" (length "foo"))
=> "The word ' foo' has 3 letters in it."
(format "The word '%7s' has %d letters in it."
"specification" (length "specification"))
=> "The word 'specification' has 13 letters in it."
Immediately after the `%' and before the optional width specifier, you can also put certain flag characters.
The flag `+' inserts a plus sign before a positive number, so that it always has a sign. A space character as flag inserts a space before a positive number. (Otherwise, positive numbers start with the first digit.) These flags are useful for ensuring that positive numbers and negative numbers use the same number of columns. They are ignored except for `%d', `%e', `%f', `%g', and if both flags are used, `+' takes precedence.
The flag `#' specifies an alternate form which depends on the format in use. For `%o', it ensures that the result begins with a `0'. For `%x' and `%X', it prefixes the result with `0x' or `0X'. For `%e', `%f', and `%g', the `#' flag means include a decimal point even if the precision is zero.
The flag `0' ensures that the padding consists of `0' characters instead of spaces. This flag is ignored for non-numerical specification characters like `%s', `%S' and `%c'. These specification characters accept the `0' flag, but still pad with spaces.
The flag `-' causes the padding inserted by the width specifier, if any, to be inserted on the right rather than the left. If both `-' and `0' are present, the `0' flag is ignored.
(format "%06d is padded on the left with zeros" 123)
=> "000123 is padded on the left with zeros"
(format "'%-6d' is padded on the right" 123)
=> "'123 ' is padded on the right"
(format "The word '%-7s' actually has %d letters in it."
"foo" (length "foo"))
=> "The word 'foo ' actually has 3 letters in it."
All the specification characters allow an optional precision before the character (after the width, if present). The precision is a decimal-point `.' followed by a digit-string. For the floating-point specifications (`%e', `%f', `%g'), the precision specifies how many decimal places to show; if zero, the decimal-point itself is also omitted. For `%s' and `%S', the precision truncates the string to the given width, so `%.3s' shows only the first three characters of the representation for object. Precision has no effect for other specification characters.
The character case functions change the case of single characters or of the contents of strings. The functions normally convert only alphabetic characters (the letters `A' through `Z' and `a' through `z', as well as non-ASCII letters); other characters are not altered. You can specify a different case conversion mapping by specifying a case table (see Case Tables).
These functions do not modify the strings that are passed to them as arguments.
The examples below use the characters `X' and `x' which have ASCII codes 88 and 120 respectively.
This function converts string-or-char, which should be either a character or a string, to lower case.
When string-or-char is a string, this function returns a new string in which each letter in the argument that is upper case is converted to lower case. When string-or-char is a character, this function returns the corresponding lower case character (an integer); if the original character is lower case, or is not a letter, the return value is equal to the original character.
(downcase "The cat in the hat") => "the cat in the hat" (downcase ?X) => 120
This function converts string-or-char, which should be either a character or a string, to upper case.
When string-or-char is a string, this function returns a new string in which each letter in the argument that is lower case is converted to upper case. When string-or-char is a character, this function returns the corresponding upper case character (an integer); if the original character is upper case, or is not a letter, the return value is equal to the original character.
(upcase "The cat in the hat") => "THE CAT IN THE HAT" (upcase ?x) => 88
This function capitalizes strings or characters. If string-or-char is a string, the function returns a new string whose contents are a copy of string-or-char in which each word has been capitalized. This means that the first character of each word is converted to upper case, and the rest are converted to lower case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (see Syntax Class Table).
When string-or-char is a character, this function does the same thing as
upcase.(capitalize "The cat in the hat") => "The Cat In The Hat" (capitalize "THE 77TH-HATTED CAT") => "The 77th-Hatted Cat" (capitalize ?x) => 88
If string-or-char is a string, this function capitalizes the initials of the words in string-or-char, without altering any letters other than the initials. It returns a new string whose contents are a copy of string-or-char, in which each word has had its initial letter converted to upper case.
The definition of a word is any sequence of consecutive characters that are assigned to the word constituent syntax class in the current syntax table (see Syntax Class Table).
When the argument to
upcase-initialsis a character,upcase-initialshas the same result asupcase.(upcase-initials "The CAT in the hAt") => "The CAT In The HAt"
See Text Comparison, for functions that compare strings; some of them ignore case differences, or can optionally ignore case differences.
You can customize case conversion by installing a special case table. A case table specifies the mapping between upper case and lower case letters. It affects both the case conversion functions for Lisp objects (see the previous section) and those that apply to text in the buffer (see Case Changes). Each buffer has a case table; there is also a standard case table which is used to initialize the case table of new buffers.
A case table is a char-table (see Char-Tables) whose subtype is
case-table. This char-table maps each character into the
corresponding lower case character. It has three extra slots, which
hold related tables:
In simple cases, all you need to specify is the mapping to lower-case; the three related tables will be calculated automatically from that one.
For some languages, upper and lower case letters are not in one-to-one correspondence. There may be two different lower case letters with the same upper case equivalent. In these cases, you need to specify the maps for both lower case and upper case.
The extra table canonicalize maps each character to a canonical equivalent; any two characters that are related by case-conversion have the same canonical equivalent character. For example, since `a' and `A' are related by case-conversion, they should have the same canonical equivalent character (which should be either `a' for both of them, or `A' for both of them).
The extra table equivalences is a map that cyclically permutes each equivalence class (of characters with the same canonical equivalent). (For ordinary ASCII, this would map `a' into `A' and `A' into `a', and likewise for each set of equivalent characters.)
When constructing a case table, you can provide nil for
canonicalize; then Emacs fills in this slot from the lower case
and upper case mappings. You can also provide nil for
equivalences; then Emacs fills in this slot from
canonicalize. In a case table that is actually in use, those
components are non-nil. Do not try to specify
equivalences without also specifying canonicalize.
Here are the functions for working with case tables:
This function makes table the standard case table, so that it will be used in any buffers created subsequently.
The
with-case-tablemacro saves the current case table, makes table the current case table, evaluates the body forms, and finally restores the case table. The return value is the value of the last form in body. The case table is restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).
Some language environments modify the case conversions of
ASCII characters; for example, in the Turkish language
environment, the ASCII capital I is downcased into
a Turkish dotless i (`ı'). This can interfere with code that requires
ordinary ASCII case conversion, such as implementations of
ASCII-based network protocols. In that case, use the
with-case-table macro with the variable ascii-case-table,
which stores the unmodified case table for the ASCII
character set.
The case table for the ASCII character set. This should not be modified by any language environment settings.
The following three functions are convenient subroutines for packages that define non-ASCII character sets. They modify the specified case table case-table; they also modify the standard syntax table. See Syntax Tables. Normally you would use these functions to change the standard case table.
This function specifies a pair of corresponding letters, one upper case and one lower case.
This function makes characters l and r a matching pair of case-invariant delimiters.
This function makes char case-invariant, with syntax syntax.
This command displays a description of the contents of the current buffer's case table.
A list represents a sequence of zero or more elements (which may be any Lisp objects). The important difference between lists and vectors is that two or more lists can share part of their structure; in addition, you can insert or delete elements in a list without copying the whole list.
Lists in Lisp are not a primitive data type; they are built up from cons cells (see Cons Cell Type). A cons cell is a data object that represents an ordered pair. That is, it has two slots, and each slot holds, or refers to, some Lisp object. One slot is known as the car, and the other is known as the cdr. (These names are traditional; see Cons Cell Type.) cdr is pronounced “could-er”.
We say that “the car of this cons cell is” whatever object its car slot currently holds, and likewise for the cdr.
A list is a series of cons cells chained together, so that each cell refers to the next one. There is one cons cell for each element of the list. By convention, the cars of the cons cells hold the elements of the list, and the cdrs are used to chain the list (this asymmetry between car and cdr is entirely a matter of convention; at the level of cons cells, the car and cdr slots have similar properties). Hence, the cdr slot of each cons cell in a list refers to the following cons cell.
Also by convention, the cdr of the last cons cell in a list is
nil. We call such a nil-terminated structure a
true list. In Emacs Lisp, the symbol nil is both a
symbol and a list with no elements. For convenience, the symbol
nil is considered to have nil as its cdr (and also
as its car).
Hence, the cdr of a true list is always a true list. The cdr of a nonempty true list is a true list containing all the elements except the first.
If the cdr of a list's last cons cell is some value other than
nil, we call the structure a dotted list, since its
printed representation would use dotted pair notation (see Dotted Pair Notation). There is one other possibility: some cons cell's
cdr could point to one of the previous cons cells in the list.
We call that structure a circular list.
For some purposes, it does not matter whether a list is true, circular or dotted. If a program doesn't look far enough down the list to see the cdr of the final cons cell, it won't care. However, some functions that operate on lists demand true lists and signal errors if given a dotted list. Most functions that try to find the end of a list enter infinite loops if given a circular list.
Because most cons cells are used as part of lists, we refer to any structure made out of cons cells as a list structure.
The following predicates test whether a Lisp object is an atom,
whether it is a cons cell or is a list, or whether it is the
distinguished object nil. (Many of these predicates can be
defined in terms of the others, but they are used so often that it is
worth having them.)
This function returns
tif object is a cons cell,nilotherwise.nilis not a cons cell, although it is a list.
This function returns
tif object is an atom,nilotherwise. All objects except cons cells are atoms. The symbolnilis an atom and is also a list; it is the only Lisp object that is both.(atom object) == (not (consp object))
This function returns
tif object is a cons cell ornil. Otherwise, it returnsnil.(listp '(1)) => t (listp '()) => t
This function is the opposite of
listp: it returnstif object is not a list. Otherwise, it returnsnil.(listp object) == (not (nlistp object))
This function returns
tif object isnil, and returnsnilotherwise. This function is identical tonot, but as a matter of clarity we usenullwhen object is considered a list andnotwhen it is considered a truth value (seenotin Combining Conditions).(null '(1)) => nil (null '()) => t
This function returns the value referred to by the first slot of the cons cell cons-cell. In other words, it returns the car of cons-cell.
As a special case, if cons-cell is
nil, this function returnsnil. Therefore, any list is a valid argument. An error is signaled if the argument is not a cons cell ornil.(car '(a b c)) => a (car '()) => nil
This function returns the value referred to by the second slot of the cons cell cons-cell. In other words, it returns the cdr of cons-cell.
As a special case, if cons-cell is
nil, this function returnsnil; therefore, any list is a valid argument. An error is signaled if the argument is not a cons cell ornil.(cdr '(a b c)) => (b c) (cdr '()) => nil
This function lets you take the car of a cons cell while avoiding errors for other data types. It returns the car of object if object is a cons cell,
nilotherwise. This is in contrast tocar, which signals an error if object is not a list.(car-safe object) == (let ((x object)) (if (consp x) (car x) nil))
This function lets you take the cdr of a cons cell while avoiding errors for other data types. It returns the cdr of object if object is a cons cell,
nilotherwise. This is in contrast tocdr, which signals an error if object is not a list.(cdr-safe object) == (let ((x object)) (if (consp x) (cdr x) nil))
This macro provides a convenient way to examine the car of a list, and take it off the list, all at once. It operates on the list stored in listname. It removes the first element from the list, saves the cdr into listname, then returns the removed element.
In the simplest case, listname is an unquoted symbol naming a list; in that case, this macro is equivalent to
(prog1 (car listname) (setq listname (cdr listname))).x => (a b c) (pop x) => a x => (b c)More generally, listname can be a generalized variable. In that case, this macro saves into listname using
setf. See Generalized Variables.For the
pushmacro, which adds an element to a list, See List Variables.
This function returns the nth element of list. Elements are numbered starting with zero, so the car of list is element number zero. If the length of list is n or less, the value is
nil.(nth 2 '(1 2 3 4)) => 3 (nth 10 '(1 2 3 4)) => nil (nth n x) == (car (nthcdr n x))The function
eltis similar, but applies to any kind of sequence. For historical reasons, it takes its arguments in the opposite order. See Sequence Functions.
This function returns the nth cdr of list. In other words, it skips past the first n links of list and returns what follows.
If n is zero,
nthcdrreturns all of list. If the length of list is n or less,nthcdrreturnsnil.(nthcdr 1 '(1 2 3 4)) => (2 3 4) (nthcdr 10 '(1 2 3 4)) => nil (nthcdr 0 '(1 2 3 4)) => (1 2 3 4)
This function returns the last link of list. The
carof this link is the list's last element. If list is null,nilis returned. If n is non-nil, the nth-to-last link is returned instead, or the whole of list if n is bigger than list's length.
This function returns the length of list, with no risk of either an error or an infinite loop. It generally returns the number of distinct cons cells in the list. However, for circular lists, the value is just an upper bound; it is often too large.
If list is not
nilor a cons cell,safe-lengthreturns 0.
The most common way to compute the length of a list, when you are not
worried that it may be circular, is with length. See Sequence Functions.
This function returns the list x with the last element, or the last n elements, removed. If n is greater than zero it makes a copy of the list so as not to damage the original list. In general,
(append (butlastx n) (lastx n))will return a list equal to x.
This is a version of
butlastthat works by destructively modifying thecdrof the appropriate element, rather than making a copy of the list.
Many functions build lists, as lists reside at the very heart of Lisp.
cons is the fundamental list-building function; however, it is
interesting to note that list is used more times in the source
code for Emacs than cons.
This function is the most basic function for building new list structure. It creates a new cons cell, making object1 the car, and object2 the cdr. It then returns the new cons cell. The arguments object1 and object2 may be any Lisp objects, but most often object2 is a list.
(cons 1 '(2)) => (1 2) (cons 1 '()) => (1) (cons 1 2) => (1 . 2)
consis often used to add a single element to the front of a list. This is called consing the element onto the list. 2 For example:(setq list (cons newelt list))Note that there is no conflict between the variable named
listused in this example and the function namedlistdescribed below; any symbol can serve both purposes.
This function creates a list with objects as its elements. The resulting list is always
nil-terminated. If no objects are given, the empty list is returned.(list 1 2 3 4 5) => (1 2 3 4 5) (list 1 2 '(3 4 5) 'foo) => (1 2 (3 4 5) foo) (list) => nil
This function creates a list of length elements, in which each element is object. Compare
make-listwithmake-string(see Creating Strings).(make-list 3 'pigs) => (pigs pigs pigs) (make-list 0 'pigs) => nil (setq l (make-list 3 '(a b))) => ((a b) (a b) (a b)) (eq (car l) (cadr l)) => t
This function returns a list containing all the elements of sequences. The sequences may be lists, vectors, bool-vectors, or strings, but the last one should usually be a list. All arguments except the last one are copied, so none of the arguments is altered. (See
nconcin Rearrangement, for a way to join lists with no copying.)More generally, the final argument to
appendmay be any Lisp object. The final argument is not copied or converted; it becomes the cdr of the last cons cell in the new list. If the final argument is itself a list, then its elements become in effect elements of the result list. If the final element is not a list, the result is a dotted list since its final cdr is notnilas required in a true list.
Here is an example of using append:
(setq trees '(pine oak))
=> (pine oak)
(setq more-trees (append '(maple birch) trees))
=> (maple birch pine oak)
trees
=> (pine oak)
more-trees
=> (maple birch pine oak)
(eq trees (cdr (cdr more-trees)))
=> t
You can see how append works by looking at a box diagram. The
variable trees is set to the list (pine oak) and then the
variable more-trees is set to the list (maple birch pine
oak). However, the variable trees continues to refer to the
original list:
more-trees trees
| |
| --- --- --- --- -> --- --- --- ---
--> | | |--> | | |--> | | |--> | | |--> nil
--- --- --- --- --- --- --- ---
| | | |
| | | |
--> maple -->birch --> pine --> oak
An empty sequence contributes nothing to the value returned by
append. As a consequence of this, a final nil argument
forces a copy of the previous argument:
trees
=> (pine oak)
(setq wood (append trees nil))
=> (pine oak)
wood
=> (pine oak)
(eq wood trees)
=> nil
This once was the usual way to copy a list, before the function
copy-sequence was invented. See Sequences Arrays Vectors.
Here we show the use of vectors and strings as arguments to append:
(append [a b] "cd" nil)
=> (a b 99 100)
With the help of apply (see Calling Functions), we can append
all the lists in a list of lists:
(apply 'append '((a b c) nil (x y z) nil))
=> (a b c x y z)
If no sequences are given, nil is returned:
(append)
=> nil
Here are some examples where the final argument is not a list:
(append '(x y) 'z)
=> (x y . z)
(append '(x y) [z])
=> (x y . [z])
The second example shows that when the final argument is a sequence but not a list, the sequence's elements do not become elements of the resulting list. Instead, the sequence becomes the final cdr, like any other non-list final argument.
This function returns a copy of the tree
tree. If tree is a cons cell, this makes a new cons cell with the same car and cdr, then recursively copies the car and cdr in the same way.Normally, when tree is anything other than a cons cell,
copy-treesimply returns tree. However, if vecp is non-nil, it copies vectors too (and operates recursively on their elements).
This returns a list of numbers starting with from and incrementing by separation, and ending at or just before to. separation can be positive or negative and defaults to 1. If to is
nilor numerically equal to from, the value is the one-element list(from). If to is less than from with a positive separation, or greater than from with a negative separation, the value isnilbecause those arguments specify an empty sequence.If separation is 0 and to is neither
nilnor numerically equal to from,number-sequencesignals an error, since those arguments specify an infinite sequence.All arguments are numbers. Floating-point arguments can be tricky, because floating-point arithmetic is inexact. For instance, depending on the machine, it may quite well happen that
(number-sequence 0.4 0.6 0.2)returns the one element list(0.4), whereas(number-sequence 0.4 0.8 0.2)returns a list with three elements. The nth element of the list is computed by the exact formula(+from(*n separation)). Thus, if one wants to make sure that to is included in the list, one can pass an expression of this exact type for to. Alternatively, one can replace to with a slightly larger value (or a slightly more negative value if separation is negative).Some examples:
(number-sequence 4 9) => (4 5 6 7 8 9) (number-sequence 9 4 -1) => (9 8 7 6 5 4) (number-sequence 9 4 -2) => (9 7 5) (number-sequence 8) => (8) (number-sequence 8 5) => nil (number-sequence 5 8 -1) => nil (number-sequence 1.5 6 2) => (1.5 3.5 5.5)
These functions, and one macro, provide convenient ways to modify a list which is stored in a variable.
This macro creates a new list whose car is element and whose cdr is the list specified by listname, and saves that list in listname. In the simplest case, listname is an unquoted symbol naming a list, and this macro is equivalent to
(setqlistname(conselementlistname)).(setq l '(a b)) => (a b) (push 'c l) => (c a b) l => (c a b)More generally,
listnamecan be a generalized variable. In that case, this macro does the equivalent of(setflistname(conselementlistname)). See Generalized Variables.For the
popmacro, which removes the first element from a list, See List Elements.
Two functions modify lists that are the values of variables.
This function sets the variable symbol by consing element onto the old value, if element is not already a member of that value. It returns the resulting list, whether updated or not. The value of symbol had better be a list already before the call.
add-to-listuses compare-fn to compare element against existing list members; if compare-fn isnil, it usesequal.Normally, if element is added, it is added to the front of symbol, but if the optional argument append is non-
nil, it is added at the end.The argument symbol is not implicitly quoted;
add-to-listis an ordinary function, likesetand unlikesetq. Quote the argument yourself if that is what you want.
Here's a scenario showing how to use add-to-list:
(setq foo '(a b))
=> (a b)
(add-to-list 'foo 'c) ;; Add c.
=> (c a b)
(add-to-list 'foo 'b) ;; No effect.
=> (c a b)
foo ;; foo was changed.
=> (c a b)
An equivalent expression for (add-to-list 'var
value) is this:
(or (member value var)
(setq var (cons value var)))
This function sets the variable symbol by inserting element into the old value, which must be a list, at the position specified by order. If element is already a member of the list, its position in the list is adjusted according to order. Membership is tested using
eq. This function returns the resulting list, whether updated or not.The order is typically a number (integer or float), and the elements of the list are sorted in non-decreasing numerical order.
order may also be omitted or
nil. Then the numeric order of element stays unchanged if it already has one; otherwise, element has no numeric order. Elements without a numeric list order are placed at the end of the list, in no particular order.Any other value for order removes the numeric order of element if it already has one; otherwise, it is equivalent to
nil.The argument symbol is not implicitly quoted;
add-to-ordered-listis an ordinary function, likesetand unlikesetq. Quote the argument yourself if necessary.The ordering information is stored in a hash table on symbol's
list-orderproperty.
Here's a scenario showing how to use add-to-ordered-list:
(setq foo '())
=> nil
(add-to-ordered-list 'foo 'a 1) ;; Add a.
=> (a)
(add-to-ordered-list 'foo 'c 3) ;; Add c.
=> (a c)
(add-to-ordered-list 'foo 'b 2) ;; Add b.
=> (a b c)
(add-to-ordered-list 'foo 'b 4) ;; Move b.
=> (a c b)
(add-to-ordered-list 'foo 'd) ;; Append d.
=> (a c b d)
(add-to-ordered-list 'foo 'e) ;; Add e.
=> (a c b e d)
foo ;; foo was changed.
=> (a c b e d)
You can modify the car and cdr contents of a cons cell with the
primitives setcar and setcdr. These are destructive
operations because they change existing list structure.
Common Lisp note: Common Lisp uses functionsrplacaandrplacdto alter list structure; they change structure the same way assetcarandsetcdr, but the Common Lisp functions return the cons cell whilesetcarandsetcdrreturn the new car or cdr.
setcar
Changing the car of a cons cell is done with setcar. When
used on a list, setcar replaces one element of a list with a
different element.
This function stores object as the new car of cons, replacing its previous car. In other words, it changes the car slot of cons to refer to object. It returns the value object. For example:
(setq x '(1 2)) => (1 2) (setcar x 4) => 4 x => (4 2)
When a cons cell is part of the shared structure of several lists, storing a new car into the cons changes one element of each of these lists. Here is an example:
;; Create two lists that are partly shared. (setq x1 '(a b c)) => (a b c) (setq x2 (cons 'z (cdr x1))) => (z b c) ;; Replace the car of a shared link. (setcar (cdr x1) 'foo) => foo x1 ; Both lists are changed. => (a foo c) x2 => (z foo c) ;; Replace the car of a link that is not shared. (setcar x1 'baz) => baz x1 ; Only one list is changed. => (baz foo c) x2 => (z foo c)
Here is a graphical depiction of the shared structure of the two lists
in the variables x1 and x2, showing why replacing b
changes them both:
--- --- --- --- --- ---
x1---> | | |----> | | |--> | | |--> nil
--- --- --- --- --- ---
| --> | |
| | | |
--> a | --> b --> c
|
--- --- |
x2--> | | |--
--- ---
|
|
--> z
Here is an alternative form of box diagram, showing the same relationship:
x1:
-------------- -------------- --------------
| car | cdr | | car | cdr | | car | cdr |
| a | o------->| b | o------->| c | nil |
| | | -->| | | | | |
-------------- | -------------- --------------
|
x2: |
-------------- |
| car | cdr | |
| z | o----
| | |
--------------
The lowest-level primitive for modifying a cdr is setcdr:
This function stores object as the new cdr of cons, replacing its previous cdr. In other words, it changes the cdr slot of cons to refer to object. It returns the value object.
Here is an example of replacing the cdr of a list with a different list. All but the first element of the list are removed in favor of a different sequence of elements. The first element is unchanged, because it resides in the car of the list, and is not reached via the cdr.
(setq x '(1 2 3))
=> (1 2 3)
(setcdr x '(4))
=> (4)
x
=> (1 4)
You can delete elements from the middle of a list by altering the
cdrs of the cons cells in the list. For example, here we delete
the second element, b, from the list (a b c), by changing
the cdr of the first cons cell:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cdr (cdr x1)))
=> (c)
x1
=> (a c)
Here is the result in box notation:
--------------------
| |
-------------- | -------------- | --------------
| car | cdr | | | car | cdr | -->| car | cdr |
| a | o----- | b | o-------->| c | nil |
| | | | | | | | |
-------------- -------------- --------------
The second cons cell, which previously held the element b, still
exists and its car is still b, but it no longer forms part
of this list.
It is equally easy to insert a new element by changing cdrs:
(setq x1 '(a b c))
=> (a b c)
(setcdr x1 (cons 'd (cdr x1)))
=> (d b c)
x1
=> (a d b c)
Here is this result in box notation:
-------------- ------------- -------------
| car | cdr | | car | cdr | | car | cdr |
| a | o | -->| b | o------->| c | nil |
| | | | | | | | | | |
--------- | -- | ------------- -------------
| |
----- --------
| |
| --------------- |
| | car | cdr | |
-->| d | o------
| | |
---------------
Here are some functions that rearrange lists destructively by modifying the cdrs of their component cons cells. These functions are destructive because they chew up the original lists passed to them as arguments, relinking their cons cells to form a new list that is the returned value.
See delq, in Sets And Lists, for another function
that modifies cons cells.
This function returns a list containing all the elements of lists. Unlike
append(see Building Lists), the lists are not copied. Instead, the last cdr of each of the lists is changed to refer to the following list. The last of the lists is not altered. For example:(setq x '(1 2 3)) => (1 2 3) (nconc x '(4 5)) => (1 2 3 4 5) x => (1 2 3 4 5)Since the last argument of
nconcis not itself modified, it is reasonable to use a constant list, such as'(4 5), as in the above example. For the same reason, the last argument need not be a list:(setq x '(1 2 3)) => (1 2 3) (nconc x 'z) => (1 2 3 . z) x => (1 2 3 . z)However, the other arguments (all but the last) must be lists.
A common pitfall is to use a quoted constant list as a non-last argument to
nconc. If you do this, your program will change each time you run it! Here is what happens:(defun add-foo (x) ; We want this function to add (nconc '(foo) x)) ;footo the front of its arg. (symbol-function 'add-foo) => (lambda (x) (nconc (quote (foo)) x)) (setq xx (add-foo '(1 2))) ; It seems to work. => (foo 1 2) (setq xy (add-foo '(3 4))) ; What happened? => (foo 1 2 3 4) (eq xx xy) => t (symbol-function 'add-foo) => (lambda (x) (nconc (quote (foo 1 2 3 4) x)))
A list can represent an unordered mathematical set—simply consider a
value an element of a set if it appears in the list, and ignore the
order of the list. To form the union of two sets, use append (as
long as you don't mind having duplicate elements). You can remove
equal duplicates using delete-dups. Other useful
functions for sets include memq and delq, and their
equal versions, member and delete.
Common Lisp note: Common Lisp has functionsunion(which avoids duplicate elements) andintersectionfor set operations. Although standard GNU Emacs Lisp does not have them, the cl-lib library provides versions. See Lists as Sets.
This function tests to see whether object is a member of list. If it is,
memqreturns a list starting with the first occurrence of object. Otherwise, it returnsnil. The letter `q' inmemqsays that it useseqto compare object against the elements of the list. For example:(memq 'b '(a b c b a)) => (b c b a) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. => nil
This function destructively removes all elements
eqto object from list, and returns the resulting list. The letter `q' indelqsays that it useseqto compare object against the elements of the list, likememqandremq.Typically, when you invoke
delq, you should use the return value by assigning it to the variable which held the original list. The reason for this is explained below.
The delq function deletes elements from the front of the list
by simply advancing down the list, and returning a sublist that starts
after those elements. For example:
(delq 'a '(a b c)) == (cdr '(a b c))
When an element to be deleted appears in the middle of the list, removing it involves changing the cdrs (see Setcdr).
(setq sample-list '(a b c (4)))
=> (a b c (4))
(delq 'a sample-list)
=> (b c (4))
sample-list
=> (a b c (4))
(delq 'c sample-list)
=> (a b (4))
sample-list
=> (a b (4))
Note that (delq 'c sample-list) modifies sample-list to
splice out the third element, but (delq 'a sample-list) does not
splice anything—it just returns a shorter list. Don't assume that a
variable which formerly held the argument list now has fewer
elements, or that it still holds the original list! Instead, save the
result of delq and use that. Most often we store the result back
into the variable that held the original list:
(setq flowers (delq 'rose flowers))
In the following example, the (4) that delq attempts to match
and the (4) in the sample-list are not eq:
(delq '(4) sample-list)
=> (a c (4))
If you want to delete elements that are equal to a given value,
use delete (see below).
This function returns a copy of list, with all elements removed which are
eqto object. The letter `q' inremqsays that it useseqto compare object against the elements oflist.(setq sample-list '(a b c a b c)) => (a b c a b c) (remq 'a sample-list) => (b c b c) sample-list => (a b c a b c)
The function
memqltests to see whether object is a member of list, comparing members with object usingeql, so floating-point elements are compared by value. If object is a member,memqlreturns a list starting with its first occurrence in list. Otherwise, it returnsnil.Compare this with
memq:(memql 1.2 '(1.1 1.2 1.3)) ;1.2and1.2areeql. => (1.2 1.3) (memq 1.2 '(1.1 1.2 1.3)) ;1.2and1.2are noteq. => nil
The following three functions are like memq, delq and
remq, but use equal rather than eq to compare
elements. See Equality Predicates.
The function
membertests to see whether object is a member of list, comparing members with object usingequal. If object is a member,memberreturns a list starting with its first occurrence in list. Otherwise, it returnsnil.Compare this with
memq:(member '(2) '((1) (2))) ;(2)and(2)areequal. => ((2)) (memq '(2) '((1) (2))) ;(2)and(2)are noteq. => nil ;; Two strings with the same contents areequal. (member "foo" '("foo" "bar")) => ("foo" "bar")
This function removes all elements
equalto object from sequence, and returns the resulting sequence.If sequence is a list,
deleteis todelqasmemberis tomemq: it usesequalto compare elements with object, likemember; when it finds an element that matches, it cuts the element out just asdelqwould. As withdelq, you should typically use the return value by assigning it to the variable which held the original list.If
sequenceis a vector or string,deletereturns a copy ofsequencewith all elementsequaltoobjectremoved.For example:
(setq l '((2) (1) (2))) (delete '(2) l) => ((1)) l => ((2) (1)) ;; If you want to changelreliably, ;; write(setq l (delete '(2) l)). (setq l '((2) (1) (2))) (delete '(1) l) => ((2) (2)) l => ((2) (2)) ;; In this case, it makes no difference whether you setl, ;; but you should do so for the sake of the other case. (delete '(2) [(2) (1) (2)]) => [(1)]
This function is the non-destructive counterpart of
delete. It returns a copy ofsequence, a list, vector, or string, with elementsequaltoobjectremoved. For example:(remove '(2) '((2) (1) (2))) => ((1)) (remove '(2) [(2) (1) (2)]) => [(1)]
Common Lisp note: The functionsmember,deleteandremovein GNU Emacs Lisp are derived from Maclisp, not Common Lisp. The Common Lisp versions do not useequalto compare elements.
This function is like
member, except that object should be a string and that it ignores differences in letter-case and text representation: upper-case and lower-case letters are treated as equal, and unibyte strings are converted to multibyte prior to comparison.
This function destructively removes all
equalduplicates from list, stores the result in list and returns it. Of severalequaloccurrences of an element in list,delete-dupskeeps the first one.
See also the function add-to-list, in List Variables,
for a way to add an element to a list stored in a variable and used as a
set.
An association list, or alist for short, records a mapping from keys to values. It is a list of cons cells called associations: the car of each cons cell is the key, and the cdr is the associated value.3
Here is an example of an alist. The key pine is associated with
the value cones; the key oak is associated with
acorns; and the key maple is associated with seeds.
((pine . cones)
(oak . acorns)
(maple . seeds))
Both the values and the keys in an alist may be any Lisp objects.
For example, in the following alist, the symbol a is
associated with the number 1, and the string "b" is
associated with the list (2 3), which is the cdr of
the alist element:
((a . 1) ("b" 2 3))
Sometimes it is better to design an alist to store the associated value in the car of the cdr of the element. Here is an example of such an alist:
((rose red) (lily white) (buttercup yellow))
Here we regard red as the value associated with rose. One
advantage of this kind of alist is that you can store other related
information—even a list of other items—in the cdr of the
cdr. One disadvantage is that you cannot use rassq (see
below) to find the element containing a given value. When neither of
these considerations is important, the choice is a matter of taste, as
long as you are consistent about it for any given alist.
The same alist shown above could be regarded as having the
associated value in the cdr of the element; the value associated
with rose would be the list (red).
Association lists are often used to record information that you might otherwise keep on a stack, since new associations may be added easily to the front of the list. When searching an association list for an association with a given key, the first one found is returned, if there is more than one.
In Emacs Lisp, it is not an error if an element of an association list is not a cons cell. The alist search functions simply ignore such elements. Many other versions of Lisp signal errors in such cases.
Note that property lists are similar to association lists in several respects. A property list behaves like an association list in which each key can occur only once. See Property Lists, for a comparison of property lists and association lists.
This function returns the first association for key in alist, comparing key against the alist elements using
equal(see Equality Predicates). It returnsnilif no association in alist has a carequalto key. For example:(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) => ((pine . cones) (oak . acorns) (maple . seeds)) (assoc 'oak trees) => (oak . acorns) (cdr (assoc 'oak trees)) => acorns (assoc 'birch trees) => nilHere is another example, in which the keys and values are not symbols:
(setq needles-per-cluster '((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine"))) (cdr (assoc 3 needles-per-cluster)) => ("Pitch Pine") (cdr (assoc 2 needles-per-cluster)) => ("Austrian Pine" "Red Pine")
The function assoc-string is much like assoc except
that it ignores certain differences between strings. See Text Comparison.
This function returns the first association with value value in alist. It returns
nilif no association in alist has a cdrequalto value.
rassocis likeassocexcept that it compares the cdr of each alist association instead of the car. You can think of this as reverseassoc, finding the key for a given value.
This function is like
associn that it returns the first association for key in alist, but it makes the comparison usingeqinstead ofequal.assqreturnsnilif no association in alist has a careqto key. This function is used more often thanassoc, sinceeqis faster thanequaland most alists use symbols as keys. See Equality Predicates.(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) => ((pine . cones) (oak . acorns) (maple . seeds)) (assq 'pine trees) => (pine . cones)On the other hand,
assqis not usually useful in alists where the keys may not be symbols:(setq leaves '(("simple leaves" . oak) ("compound leaves" . horsechestnut))) (assq "simple leaves" leaves) => nil (assoc "simple leaves" leaves) => ("simple leaves" . oak)
This function is like
assq, but instead of returning the entire association for key,(key.value), it returns just the value. If key is not found in alist it returns default.This is a generalized variable (see Generalized Variables) that can be used to change a value with
setf. When using it to set a value, optional argument remove non-nil means to remove key from alist if the new value iseqlto default.
This function returns the first association with value value in alist. It returns
nilif no association in alist has a cdreqto value.
rassqis likeassqexcept that it compares the cdr of each alist association instead of the car. You can think of this as reverseassq, finding the key for a given value.For example:
(setq trees '((pine . cones) (oak . acorns) (maple . seeds))) (rassq 'acorns trees) => (oak . acorns) (rassq 'spores trees) => nil
rassqcannot search for a value stored in the car of the cdr of an element:(setq colors '((rose red) (lily white) (buttercup yellow))) (rassq 'white colors) => nilIn this case, the cdr of the association
(lily white)is not the symbolwhite, but rather the list(white). This becomes clearer if the association is written in dotted pair notation:(lily white) == (lily . (white))
This function searches alist for a match for key. For each element of alist, it compares the element (if it is an atom) or the element's car (if it is a cons) against key, by calling test with two arguments: the element or its car, and key. The arguments are passed in that order so that you can get useful results using
string-matchwith an alist that contains regular expressions (see Regexp Search). If test is omitted ornil,equalis used for comparison.If an alist element matches key by this criterion, then
assoc-defaultreturns a value based on this element. If the element is a cons, then the value is the element's cdr. Otherwise, the return value is default.If no alist element matches key,
assoc-defaultreturnsnil.
This function returns a two-level deep copy of alist: it creates a new copy of each association, so that you can alter the associations of the new alist without changing the old one.
(setq needles-per-cluster '((2 . ("Austrian Pine" "Red Pine")) (3 . ("Pitch Pine")) (5 . ("White Pine")))) => ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (setq copy (copy-alist needles-per-cluster)) => ((2 "Austrian Pine" "Red Pine") (3 "Pitch Pine") (5 "White Pine")) (eq needles-per-cluster copy) => nil (equal needles-per-cluster copy) => t (eq (car needles-per-cluster) (car copy)) => nil (cdr (car (cdr needles-per-cluster))) => ("Pitch Pine") (eq (cdr (car (cdr needles-per-cluster))) (cdr (car (cdr copy)))) => tThis example shows how
copy-alistmakes it possible to change the associations of one copy without affecting the other:(setcdr (assq 3 copy) '("Martian Vacuum Pine")) (cdr (assq 3 needles-per-cluster)) => ("Pitch Pine")
This function deletes from alist all the elements whose car is
eqto key, much as if you useddelqto delete each such element one by one. It returns the shortened alist, and often modifies the original list structure of alist. For correct results, use the return value ofassq-delete-allrather than looking at the saved value of alist.(setq alist '((foo 1) (bar 2) (foo 3) (lose 4))) => ((foo 1) (bar 2) (foo 3) (lose 4)) (assq-delete-all 'foo alist) => ((bar 2) (lose 4)) alist => ((foo 1) (bar 2) (lose 4))
This function deletes from alist all the elements whose cdr is
eqto value. It returns the shortened alist, and often modifies the original list structure of alist.rassq-delete-allis likeassq-delete-allexcept that it compares the cdr of each alist association instead of the car.
A property list (plist for short) is a list of paired elements. Each of the pairs associates a property name (usually a symbol) with a property or value. Here is an example of a property list:
(pine cones numbers (1 2 3) color "blue")
This property list associates pine with cones,
numbers with (1 2 3), and color with
"blue". The property names and values can be any Lisp objects,
but the names are usually symbols (as they are in this example).
Property lists are used in several contexts. For instance, the
function put-text-property takes an argument which is a
property list, specifying text properties and associated values which
are to be applied to text in a string or buffer. See Text Properties.
Another prominent use of property lists is for storing symbol properties. Every symbol possesses a list of properties, used to record miscellaneous information about the symbol; these properties are stored in the form of a property list. See Symbol Properties.
Association lists (see Association Lists) are very similar to property lists. In contrast to association lists, the order of the pairs in the property list is not significant, since the property names must be distinct.
Property lists are better than association lists for attaching
information to various Lisp function names or variables. If your
program keeps all such information in one association list, it will
typically need to search that entire list each time it checks for an
association for a particular Lisp function name or variable, which
could be slow. By contrast, if you keep the same information in the
property lists of the function names or variables themselves, each
search will scan only the length of one property list, which is
usually short. This is why the documentation for a variable is
recorded in a property named variable-documentation. The byte
compiler likewise uses properties to record those functions needing
special treatment.
However, association lists have their own advantages. Depending on your application, it may be faster to add an association to the front of an association list than to update a property. All properties for a symbol are stored in the same property list, so there is a possibility of a conflict between different uses of a property name. (For this reason, it is a good idea to choose property names that are probably unique, such as by beginning the property name with the program's usual name-prefix for variables and functions.) An association list may be used like a stack where associations are pushed on the front of the list and later discarded; this is not possible with a property list.
The following functions can be used to manipulate property lists.
They all compare property names using eq.
This returns the value of the property property stored in the property list plist. It accepts a malformed plist argument. If property is not found in the plist, it returns
nil. For example,(plist-get '(foo 4) 'foo) => 4 (plist-get '(foo 4 bad) 'foo) => 4 (plist-get '(foo 4 bad) 'bad) => nil (plist-get '(foo 4 bad) 'bar) => nil
This stores value as the value of the property property in the property list plist. It may modify plist destructively, or it may construct a new list structure without altering the old. The function returns the modified property list, so you can store that back in the place where you got plist. For example,
(setq my-plist '(bar t foo 4)) => (bar t foo 4) (setq my-plist (plist-put my-plist 'foo 69)) => (bar t foo 69) (setq my-plist (plist-put my-plist 'quux '(a))) => (bar t foo 69 quux (a))
Like
plist-getexcept that it compares properties usingequalinstead ofeq.
Like
plist-putexcept that it compares properties usingequalinstead ofeq.
This returns non-
nilif plist contains the given property. Unlikeplist-get, this allows you to distinguish between a missing property and a property with the valuenil. The value is actually the tail of plist whosecaris property.
The sequence type is the union of two other Lisp types: lists and arrays. In other words, any list is a sequence, and any array is a sequence. The common property that all sequences have is that each is an ordered collection of elements.
An array is a fixed-length object with a slot for each of its elements. All the elements are accessible in constant time. The four types of arrays are strings, vectors, char-tables and bool-vectors.
A list is a sequence of elements, but it is not a single primitive object; it is made of cons cells, one cell per element. Finding the nth element requires looking through n cons cells, so elements farther from the beginning of the list take longer to access. But it is possible to add elements to the list, or remove elements.
The following diagram shows the relationship between these types:
_____________________________________________
| |
| Sequence |
| ______ ________________________________ |
| | | | | |
| | List | | Array | |
| | | | ________ ________ | |
| |______| | | | | | | |
| | | Vector | | String | | |
| | |________| |________| | |
| | ____________ _____________ | |
| | | | | | | |
| | | Char-table | | Bool-vector | | |
| | |____________| |_____________| | |
| |________________________________| |
|_____________________________________________|
This section describes functions that accept any kind of sequence.
This function returns
tif object is a list, vector, string, bool-vector, or char-table,nilotherwise.
This function returns the number of elements in sequence. If sequence is a dotted list, a
wrong-type-argumenterror is signaled. Circular lists may cause an infinite loop. For a char-table, the value returned is always one more than the maximum Emacs character code.See Definition of safe-length, for the related function
safe-length.(length '(1 2 3)) => 3 (length ()) => 0 (length "foobar") => 6 (length [1 2 3]) => 3 (length (make-bool-vector 5 nil)) => 5
See also string-bytes, in Text Representations.
If you need to compute the width of a string on display, you should use
string-width (see Size of Displayed Text), not length,
since length only counts the number of characters, but does not
account for the display width of each character.
This function returns the element of sequence indexed by index. Legitimate values of index are integers ranging from 0 up to one less than the length of sequence. If sequence is a list, out-of-range values behave as for
nth. See Definition of nth. Otherwise, out-of-range values trigger anargs-out-of-rangeerror.(elt [1 2 3 4] 2) => 3 (elt '(1 2 3 4) 2) => 3 ;; We usestringto show clearly which charactereltreturns. (string (elt "1234" 2)) => "3" (elt [1 2 3 4] 4) error--> Args out of range: [1 2 3 4], 4 (elt [1 2 3 4] -1) error--> Args out of range: [1 2 3 4], -1This function generalizes
aref(see Array Functions) andnth(see Definition of nth).
This function returns a copy of sequence. The copy is the same type of object as the original sequence, and it has the same elements in the same order.
Storing a new element into the copy does not affect the original sequence, and vice versa. However, the elements of the new sequence are not copies; they are identical (
eq) to the elements of the original. Therefore, changes made within these elements, as found via the copied sequence, are also visible in the original sequence.If the sequence is a string with text properties, the property list in the copy is itself a copy, not shared with the original's property list. However, the actual values of the properties are shared. See Text Properties.
This function does not work for dotted lists. Trying to copy a circular list may cause an infinite loop.
See also
appendin Building Lists,concatin Creating Strings, andvconcatin Vector Functions, for other ways to copy sequences.(setq bar '(1 2)) => (1 2) (setq x (vector 'foo bar)) => [foo (1 2)] (setq y (copy-sequence x)) => [foo (1 2)] (eq x y) => nil (equal x y) => t (eq (elt x 1) (elt y 1)) => t ;; Replacing an element of one sequence. (aset x 0 'quux) x => [quux (1 2)] y => [foo (1 2)] ;; Modifying the inside of a shared element. (setcar (aref x 1) 69) x => [quux (69 2)] y => [foo (69 2)]
This function creates a new sequence whose elements are the elements of sequence, but in reverse order. The original argument sequence is not altered. Note that char-tables cannot be reversed.
(setq x '(1 2 3 4)) => (1 2 3 4) (reverse x) => (4 3 2 1) x => (1 2 3 4) (setq x [1 2 3 4]) => [1 2 3 4] (reverse x) => [4 3 2 1] x => [1 2 3 4] (setq x "xyzzy") => "xyzzy" (reverse x) => "yzzyx" x => "xyzzy"
This function reverses the order of the elements of sequence. Unlike
reversethe original sequence may be modified.For example:
(setq x '(a b c)) => (a b c) x => (a b c) (nreverse x) => (c b a) ;; The cons cell that was first is now last. x => (a)To avoid confusion, we usually store the result of
nreverseback in the same variable which held the original list:(setq x (nreverse x))Here is the
nreverseof our favorite example,(a b c), presented graphically:Original list head: Reversed list: ------------- ------------- ------------ | car | cdr | | car | cdr | | car | cdr | | a | nil |<-- | b | o |<-- | c | o | | | | | | | | | | | | | | ------------- | --------- | - | -------- | - | | | | ------------- ------------For the vector, it is even simpler because you don't need setq:
(setq x [1 2 3 4]) => [1 2 3 4] (nreverse x) => [4 3 2 1] x => [4 3 2 1]Note that unlike
reverse, this function doesn't work with strings. Although you can alter string data by usingaset, it is strongly encouraged to treat strings as immutable.
This function sorts sequence stably. Note that this function doesn't work for all sequences; it may be used only for lists and vectors. If sequence is a list, it is modified destructively. This functions returns the sorted sequence and compares elements using predicate. A stable sort is one in which elements with equal sort keys maintain their relative order before and after the sort. Stability is important when successive sorts are used to order elements according to different criteria.
The argument predicate must be a function that accepts two arguments. It is called with two elements of sequence. To get an increasing order sort, the predicate should return non-
nilif the first element is “less” than the second, ornilif not.The comparison function predicate must give reliable results for any given pair of arguments, at least within a single call to
sort. It must be antisymmetric; that is, if a is less than b, b must not be less than a. It must be transitive—that is, if a is less than b, and b is less than c, then a must be less than c. If you use a comparison function which does not meet these requirements, the result ofsortis unpredictable.The destructive aspect of
sortfor lists is that it rearranges the cons cells forming sequence by changing cdrs. A nondestructive sort function would create new cons cells to store the elements in their sorted order. If you wish to make a sorted copy without destroying the original, copy it first withcopy-sequenceand then sort.Sorting does not change the cars of the cons cells in sequence; the cons cell that originally contained the element
ain sequence still hasain its car after sorting, but it now appears in a different position in the list due to the change of cdrs. For example:(setq nums '(1 3 2 6 5 4 0)) => (1 3 2 6 5 4 0) (sort nums '<) => (0 1 2 3 4 5 6) nums => (1 2 3 4 5 6)Warning: Note that the list in
numsno longer contains 0; this is the same cons cell that it was before, but it is no longer the first one in the list. Don't assume a variable that formerly held the argument now holds the entire sorted list! Instead, save the result ofsortand use that. Most often we store the result back into the variable that held the original list:(setq nums (sort nums '<))For the better understanding of what stable sort is, consider the following vector example. After sorting, all items whose
caris 8 are grouped at the beginning ofvector, but their relative order is preserved. All items whosecaris 9 are grouped at the end ofvector, but their relative order is also preserved:(setq vector (vector '(8 . "xxx") '(9 . "aaa") '(8 . "bbb") '(9 . "zzz") '(9 . "ppp") '(8 . "ttt") '(8 . "eee") '(9 . "fff"))) => [(8 . "xxx") (9 . "aaa") (8 . "bbb") (9 . "zzz") (9 . "ppp") (8 . "ttt") (8 . "eee") (9 . "fff")] (sort vector (lambda (x y) (< (car x) (car y)))) => [(8 . "xxx") (8 . "bbb") (8 . "ttt") (8 . "eee") (9 . "aaa") (9 . "zzz") (9 . "ppp") (9 . "fff")]See Sorting, for more functions that perform sorting. See
documentationin Accessing Documentation, for a useful example ofsort.
The seq.el library provides the following additional sequence
manipulation macros and functions, prefixed with seq-. To use
them, you must first load the seq library.
All functions defined in this library are free of side-effects; i.e., they do not modify any sequence (list, vector, or string) that you pass as an argument. Unless otherwise stated, the result is a sequence of the same type as the input. For those functions that take a predicate, this should be a function of one argument.
The seq.el library can be extended to work with additional
types of sequential data-structures. For that purpose, all functions
are defined using cl-defgeneric. See Generic Functions, for
more details about using cl-defgeneric for adding extensions.
This function returns the element of sequence at the specified index, which is an integer whose valid value range is zero to one less than the length of sequence. For out-of-range values on built-in sequence types,
seq-eltbehaves likeelt. For the details, see Definition of elt.(seq-elt [1 2 3 4] 2) => 3
seq-eltreturns places settable usingsetf(see Setting Generalized Variables).(setq vec [1 2 3 4]) (setf (seq-elt vec 2) 5) vec => [1 2 5 4]
This function returns the number of elements in sequence. For built-in sequence types,
seq-lengthbehaves likelength. See Definition of length.
This function returns non-
nilif sequence is a sequence (a list or array), or any additional type of sequence defined via seq.el generic functions.(seqp [1 2]) => t (seqp 2) => nil
This function returns all but the first n (an integer) elements of sequence. If n is negative or zero, the result is sequence.
(seq-drop [1 2 3 4 5 6] 3) => [4 5 6] (seq-drop "hello world" -4) => "hello world"
This function returns the first n (an integer) elements of sequence. If n is negative or zero, the result is
nil.(seq-take '(1 2 3 4) 3) => (1 2 3) (seq-take [1 2 3 4] 0) => []
This function returns the members of sequence in order, stopping before the first one for which predicate returns
nil.(seq-take-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2)) => (1 2 3) (seq-take-while (lambda (elt) (> elt 0)) [-1 4 6]) => []
This function returns the members of sequence in order, starting from the first one for which predicate returns
nil.(seq-drop-while (lambda (elt) (> elt 0)) '(1 2 3 -1 -2)) => (-1 -2) (seq-drop-while (lambda (elt) (< elt 0)) [1 4 6]) => [1 4 6]
This function applies function to each element of sequence in turn (presumably for side effects), and returns sequence.
This function returns the result of applying function to each element of sequence. The returned value is a list.
(seq-map #'1+ '(2 4 6)) => (3 5 7) (seq-map #'symbol-name [foo bar]) => ("foo" "bar")
This function returns the result of applying function to each element of sequences. The arity (see sub-arity) of function must match the number of sequences. Mapping stops at the end of the shortest sequence, and the returned value is a list.
(seq-mapn #'+ '(2 4 6) '(20 40 60)) => (22 44 66) (seq-mapn #'concat '("moskito" "bite") ["bee" "sting"]) => ("moskitobee" "bitesting")
This function returns a list of all the elements in sequence for which predicate returns non-
nil.(seq-filter (lambda (elt) (> elt 0)) [1 -1 3 -3 5]) => (1 3 5) (seq-filter (lambda (elt) (> elt 0)) '(-1 -3 -5)) => nil
This function returns a list of all the elements in sequence for which predicate returns
nil.(seq-remove (lambda (elt) (> elt 0)) [1 -1 3 -3 5]) => (-1 -3) (seq-remove (lambda (elt) (< elt 0)) '(-1 -3 -5)) => nil
This function returns the result of calling function with initial-value and the first element of sequence, then calling function with that result and the second element of sequence, then with that result and the third element of sequence, etc. function should be a function of two arguments. If sequence is empty, this returns initial-value without calling function.
(seq-reduce #'+ [1 2 3 4] 0) => 10 (seq-reduce #'+ '(1 2 3 4) 5) => 15 (seq-reduce #'+ '() 3) => 3
This function returns the first non-
nilvalue returned by applying predicate to each element of sequence in turn.(seq-some #'numberp ["abc" 1 nil]) => t (seq-some #'numberp ["abc" "def"]) => nil (seq-some #'null ["abc" 1 nil]) => t (seq-some #'1+ [2 4 6]) => 3
This function returns the first element in sequence for which predicate returns non-
nil. If no element matches predicate, the function returns default.Note that this function has an ambiguity if the found element is identical to default, as in that case it cannot be known whether an element was found or not.
(seq-find #'numberp ["abc" 1 nil]) => 1 (seq-find #'numberp ["abc" "def"]) => nil
This function returns non-
nilif applying predicate to every element of sequence returns non-nil.(seq-every-p #'numberp [2 4 6]) => t (seq-some #'numberp [2 4 "6"]) => nil
This function returns non-
nilif sequence is empty.(seq-empty-p "not empty") => nil (seq-empty-p "") => t
This function returns the number of elements in sequence for which predicate returns non-
nil.(seq-count (lambda (elt) (> elt 0)) [-1 2 0 3 -2]) => 2
This function returns a copy of sequence that is sorted according to function, a function of two arguments that returns non-
nilif the first argument should sort before the second.
This function returns the first element in sequence that is equal to elt. If the optional argument function is non-
nil, it is a function of two arguments to use instead of the defaultequal.(seq-contains '(symbol1 symbol2) 'symbol1) => symbol1 (seq-contains '(symbol1 symbol2) 'symbol3) => nil
This function returns the index of the first element in sequence that is equal to elt. If the optional argument function is non-
nil, it is a function of two arguments to use instead of the defaultequal.(seq-position '(a b c) 'b) => 1 (seq-position '(a b c) 'd) => nil
This function returns a list of the elements of sequence with duplicates removed. If the optional argument function is non-
nil, it is a function of two arguments to use instead of the defaultequal.(seq-uniq '(1 2 2 1 3)) => (1 2 3) (seq-uniq '(1 2 2.0 1.0) #'=) => [3 4]
This function returns a subset of sequence from start to end, both integers (end defaults to the last element). If start or end is negative, it counts from the end of sequence.
(seq-subseq '(1 2 3 4 5) 1) => (2 3 4 5) (seq-subseq '[1 2 3 4 5] 1 3) => [2 3] (seq-subseq '[1 2 3 4 5] -3 -1) => [3 4]
This function returns a sequence of type type made of the concatenation of sequences. type may be:
vector,listorstring.(seq-concatenate 'list '(1 2) '(3 4) [5 6]) => (1 2 3 5 6) (seq-concatenate 'string "Hello " "world") => "Hello world"
This function returns the result of applying
seq-concatenateto the result of applying function to each element of sequence. The result is a sequence of type type, or a list if type isnil.(seq-mapcat #'seq-reverse '((3 2 1) (6 5 4))) => (1 2 3 4 5 6)
This function returns a list of the elements of sequence grouped into sub-sequences of length n. The last sequence may contain less elements than n. n must be an integer. If n is a negative integer or 0, the return value is
nil.(seq-partition '(0 1 2 3 4 5 6 7) 3) => ((0 1 2) (3 4 5) (6 7))
This function returns a list of the elements that appear both in sequence1 and sequence2. If the optional argument function is non-
nil, it is a function of two arguments to use to compare elements instead of the defaultequal.(seq-intersection [2 3 4 5] [1 3 5 6 7]) => (3 5)
This function returns a list of the elements that appear in sequence1 but not in sequence2. If the optional argument function is non-
nil, it is a function of two arguments to use to compare elements instead of the defaultequal.(seq-difference '(2 3 4 5) [1 3 5 6 7]) => (2 4)
This function separates the elements of sequence into an alist whose keys are the result of applying function to each element of sequence. Keys are compared using
equal.(seq-group-by #'integerp '(1 2.1 3 2 3.2)) => ((t 1 3 2) (nil 2.1 3.2)) (seq-group-by #'car '((a 1) (b 2) (a 3) (c 4))) => ((b (b 2)) (a (a 1) (a 3)) (c (c 4)))
This function converts the sequence sequence into a sequence of type type. type can be one of the following symbols:
vector,stringorlist.(seq-into [1 2 3] 'list) => (1 2 3) (seq-into nil 'vector) => [] (seq-into "hello" 'vector) => [104 101 108 108 111]
This function returns the smallest element of sequence. The elements of sequence must be numbers or markers (see Markers).
(seq-min [3 1 2]) => 1 (seq-min "Hello") => 72
This function returns the largest element of sequence. The elements of sequence must be numbers or markers.
(seq-max [1 3 2]) => 3 (seq-max "Hello") => 111
This macro is like
dolist(see dolist), except that sequence can be a list, vector or string. This is primarily useful for side-effects.
This macro binds the variables defined in arguments to the elements of sequence. arguments can themselves include sequences, allowing for nested destructuring.
The arguments sequence can also include the
&restmarker followed by a variable name to be bound to the rest ofsequence.(seq-let [first second] [1 2 3 4] (list first second)) => (1 2) (seq-let (_ a _ b) '(1 2 3 4) (list a b)) => (2 4) (seq-let [a [b [c]]] [1 [2 [3]]] (list a b c)) => (1 2 3) (seq-let [a b &rest others] [1 2 3 4] others) => [3 4]
An array object has slots that hold a number of other Lisp objects, called the elements of the array. Any element of an array may be accessed in constant time. In contrast, the time to access an element of a list is proportional to the position of that element in the list.
Emacs defines four types of array, all one-dimensional:
strings (see String Type), vectors (see Vector Type), bool-vectors (see Bool-Vector Type), and
char-tables (see Char-Table Type). Vectors and char-tables
can hold elements of any type, but strings can only hold characters,
and bool-vectors can only hold t and nil.
All four kinds of array share these characteristics:
aref and aset, respectively (see Array Functions).
When you create an array, other than a char-table, you must specify its length. You cannot specify the length of a char-table, because that is determined by the range of character codes.
In principle, if you want an array of text characters, you could use either a string or a vector. In practice, we always choose strings for such applications, for four reasons:
By contrast, for an array of keyboard input characters (such as a key sequence), a vector may be necessary, because many keyboard input characters are outside the range that will fit in a string. See Key Sequence Input.
In this section, we describe the functions that accept all types of arrays.
This function returns
tif object is an array (i.e., a vector, a string, a bool-vector or a char-table).(arrayp [a]) => t (arrayp "asdf") => t (arrayp (syntax-table)) ;; A char-table. => t
This function returns the indexth element of array. The first element is at index zero.
(setq primes [2 3 5 7 11 13]) => [2 3 5 7 11 13] (aref primes 4) => 11 (aref "abcdefg" 1) => 98 ; `b' is ASCII code 98.See also the function
elt, in Sequence Functions.
This function sets the indexth element of array to be object. It returns object.
(setq w [foo bar baz]) => [foo bar baz] (aset w 0 'fu) => fu w => [fu bar baz] (setq x "asdfasfd") => "asdfasfd" (aset x 3 ?Z) => 90 x => "asdZasfd"If array is a string and object is not a character, a
wrong-type-argumenterror results. The function converts a unibyte string to multibyte if necessary to insert a character.
This function fills the array array with object, so that each element of array is object. It returns array.
(setq a [a b c d e f g]) => [a b c d e f g] (fillarray a 0) => [0 0 0 0 0 0 0] a => [0 0 0 0 0 0 0] (setq s "When in the course") => "When in the course" (fillarray s ?-) => "------------------"If array is a string and object is not a character, a
wrong-type-argumenterror results.
The general sequence functions copy-sequence and length
are often useful for objects known to be arrays. See Sequence Functions.
A vector is a general-purpose array whose elements can be any Lisp objects. (By contrast, the elements of a string can only be characters. See Strings and Characters.) Vectors are used in Emacs for many purposes: as key sequences (see Key Sequences), as symbol-lookup tables (see Creating Symbols), as part of the representation of a byte-compiled function (see Byte Compilation), and more.
Like other arrays, vectors use zero-origin indexing: the first element has index 0.
Vectors are printed with square brackets surrounding the elements.
Thus, a vector whose elements are the symbols a, b and
a is printed as [a b a]. You can write vectors in the
same way in Lisp input.
A vector, like a string or a number, is considered a constant for evaluation: the result of evaluating it is the same vector. This does not evaluate or even examine the elements of the vector. See Self-Evaluating Forms.
Here are examples illustrating these principles:
(setq avector [1 two '(three) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(eval avector)
=> [1 two (quote (three)) "four" [five]]
(eq avector (eval avector))
=> t
Here are some functions that relate to vectors:
This function returns
tif object is a vector.(vectorp [a]) => t (vectorp "asdf") => nil
This function creates and returns a vector whose elements are the arguments, objects.
(vector 'foo 23 [bar baz] "rats") => [foo 23 [bar baz] "rats"] (vector) => []
This function returns a new vector consisting of length elements, each initialized to object.
(setq sleepy (make-vector 9 'Z)) => [Z Z Z Z Z Z Z Z Z]
This function returns a new vector containing all the elements of sequences. The arguments sequences may be true lists, vectors, strings or bool-vectors. If no sequences are given, the empty vector is returned.
The value is either the empty vector, or is a newly constructed nonempty vector that is not
eqto any existing vector.(setq a (vconcat '(A B C) '(D E F))) => [A B C D E F] (eq a (vconcat a)) => nil (vconcat) => [] (vconcat [A B C] "aa" '(foo (6 7))) => [A B C 97 97 foo (6 7)]The
vconcatfunction also allows byte-code function objects as arguments. This is a special feature to make it easy to access the entire contents of a byte-code function object. See Byte-Code Objects.For other concatenation functions, see
mapconcatin Mapping Functions,concatin Creating Strings, andappendin Building Lists.
The append function also provides a way to convert a vector into a
list with the same elements:
(setq avector [1 two (quote (three)) "four" [five]])
=> [1 two (quote (three)) "four" [five]]
(append avector nil)
=> (1 two (quote (three)) "four" [five])
A char-table is much like a vector, except that it is indexed by
character codes. Any valid character code, without modifiers, can be
used as an index in a char-table. You can access a char-table's
elements with aref and aset, as with any array. In
addition, a char-table can have extra slots to hold additional
data not associated with particular character codes. Like vectors,
char-tables are constants when evaluated, and can hold elements of any
type.
Each char-table has a subtype, a symbol, which serves two purposes:
display-table
as the subtype, and syntax tables are char-tables with
syntax-table as the subtype. The subtype can be queried using
the function char-table-subtype, described below.
char-table-extra-slots symbol property (see Symbol Properties), whose value should be an integer between 0 and 10. If
the subtype has no such symbol property, the char-table has no extra
slots.
A char-table can have a parent, which is another char-table. If
it does, then whenever the char-table specifies nil for a
particular character c, it inherits the value specified in the
parent. In other words, (aref char-table c) returns
the value from the parent of char-table if char-table itself
specifies nil.
A char-table can also have a default value. If so, then
(aref char-table c) returns the default value
whenever the char-table does not specify any other non-nil value.
Return a newly-created char-table, with subtype subtype (a symbol). Each element is initialized to init, which defaults to
nil. You cannot alter the subtype of a char-table after the char-table is created.There is no argument to specify the length of the char-table, because all char-tables have room for any valid character code as an index.
If subtype has the
char-table-extra-slotssymbol property, that specifies the number of extra slots in the char-table. This should be an integer between 0 and 10; otherwise,make-char-tableraises an error. If subtype has nochar-table-extra-slotssymbol property (see Property Lists), the char-table has no extra slots.
This function returns
tif object is a char-table, andnilotherwise.
There is no special function to access default values in a char-table.
To do that, use char-table-range (see below).
This function returns the parent of char-table. The parent is always either
nilor another char-table.
This function sets the parent of char-table to new-parent.
This function returns the contents of extra slot n (zero based) of char-table. The number of extra slots in a char-table is determined by its subtype.
This function stores value in extra slot n (zero based) of char-table.
A char-table can specify an element value for a single character code; it can also specify a value for an entire character set.
This returns the value specified in char-table for a range of characters range. Here are the possibilities for range:
nil- Refers to the default value.
- char
- Refers to the element for character char (supposing char is a valid character code).
(from.to)- A cons cell refers to all the characters in the inclusive range `[from..to]'.
This function sets the value in char-table for a range of characters range. Here are the possibilities for range:
nil- Refers to the default value.
t- Refers to the whole range of character codes.
- char
- Refers to the element for character char (supposing char is a valid character code).
(from.to)- A cons cell refers to all the characters in the inclusive range `[from..to]'.
This function calls its argument function for each element of char-table that has a non-
nilvalue. The call to function is with two arguments, a key and a value. The key is a possible range argument forchar-table-range—either a valid character or a cons cell(from.to), specifying a range of characters that share the same value. The value is what(char-table-rangechar-table key)returns.Overall, the key-value pairs passed to function describe all the values stored in char-table.
The return value is always
nil; to make calls tomap-char-tableuseful, function should have side effects. For example, here is how to examine the elements of the syntax table:(let (accumulator) (map-char-table #'(lambda (key value) (setq accumulator (cons (list (if (consp key) (list (car key) (cdr key)) key) value) accumulator))) (syntax-table)) accumulator) => (((2597602 4194303) (2)) ((2597523 2597601) (3)) ... (65379 (5 . 65378)) (65378 (4 . 65379)) (65377 (1)) ... (12 (0)) (11 (3)) (10 (12)) (9 (0)) ((0 8) (3)))
A bool-vector is much like a vector, except that it stores only the
values t and nil. If you try to store any non-nil
value into an element of the bool-vector, the effect is to store
t there. As with all arrays, bool-vector indices start from 0,
and the length cannot be changed once the bool-vector is created.
Bool-vectors are constants when evaluated.
Several functions work specifically with bool-vectors; aside from that, you manipulate them with same functions used for other kinds of arrays.
Return a new bool-vector of length elements, each one initialized to initial.
This function creates and returns a bool-vector whose elements are the arguments, objects.
There are also some bool-vector set operation functions, described below:
Return bitwise exclusive or of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.
Return bitwise or of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.
Return bitwise and of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.
Return set difference of bool vectors a and b. If optional argument c is given, the result of this operation is stored into c. All arguments should be bool vectors of the same length.
Return set complement of bool vector a. If optional argument b is given, the result of this operation is stored into b. All arguments should be bool vectors of the same length.
Return
tif everytvalue in a is also t in b,nilotherwise. All arguments should be bool vectors of the same length.
Return the number of consecutive elements in a equal b starting at i.
ais a bool vector, b istornil, and i is an index intoa.
Return the number of elements that are
tin bool vector a.
The printed form represents up to 8 boolean values as a single character:
(bool-vector t nil t nil)
=> #&4"^E"
(bool-vector)
=> #&0""
You can use vconcat to print a bool-vector like other vectors:
(vconcat (bool-vector nil t nil t))
=> [nil t nil t]
Here is another example of creating, examining, and updating a bool-vector:
(setq bv (make-bool-vector 5 t))
=> #&5"^_"
(aref bv 1)
=> t
(aset bv 3 nil)
=> nil
bv
=> #&5"^W"
These results make sense because the binary codes for control-_ and control-W are 11111 and 10111, respectively.
A ring is a fixed-size data structure that supports insertion,
deletion, rotation, and modulo-indexed reference and traversal. An
efficient ring data structure is implemented by the ring
package. It provides the functions listed in this section.
Note that several rings in Emacs, like the kill ring and the
mark ring, are actually implemented as simple lists, not using
the ring package; thus the following functions won't work on
them.
This returns a new ring capable of holding size objects. size should be an integer.
This returns the number of objects that ring currently contains. The value will never exceed that returned by
ring-size.
This returns a new ring which is a copy of ring. The new ring contains the same (
eq) objects as ring.
The newest element in the ring always has index 0. Higher indices correspond to older elements. Indices are computed modulo the ring length. Index −1 corresponds to the oldest element, −2 to the next-oldest, and so forth.
This returns the object in ring found at index index. index may be negative or greater than the ring length. If ring is empty,
ring-refsignals an error.
This inserts object into ring, making it the newest element, and returns object.
If the ring is full, insertion removes the oldest element to make room for the new element.
Remove an object from ring, and return that object. The argument index specifies which item to remove; if it is
nil, that means to remove the oldest item. If ring is empty,ring-removesignals an error.
This inserts object into ring, treating it as the oldest element. The return value is not significant.
If the ring is full, this function removes the newest element to make room for the inserted element.
If you are careful not to exceed the ring size, you can use the ring as a first-in-first-out queue. For example:
(let ((fifo (make-ring 5)))
(mapc (lambda (obj) (ring-insert fifo obj))
'(0 one "two"))
(list (ring-remove fifo) t
(ring-remove fifo) t
(ring-remove fifo)))
=> (0 t one t "two")
A hash table is a very fast kind of lookup table, somewhat like an alist (see Association Lists) in that it maps keys to corresponding values. It differs from an alist in these ways:
Emacs Lisp provides a general-purpose hash table data type, along with a series of functions for operating on them. Hash tables have a special printed representation, which consists of `#s' followed by a list specifying the hash table properties and contents. See Creating Hash. (Hash notation, the initial `#' character used in the printed representations of objects with no read representation, has nothing to do with hash tables. See Printed Representation.)
Obarrays are also a kind of hash table, but they are a different type of object and are used only for recording interned symbols (see Creating Symbols).
The principal function for creating a hash table is
make-hash-table.
This function creates a new hash table according to the specified arguments. The arguments should consist of alternating keywords (particular symbols recognized specially) and values corresponding to them.
Several keywords make sense in
make-hash-table, but the only two that you really need to know about are:testand:weakness.
:testtest- This specifies the method of key lookup for this hash table. The default is
eql;eqandequalare other alternatives:
eql- Keys which are numbers are the same if they are
equal, that is, if they are equal in value and either both are integers or both are floating point; otherwise, two distinct objects are never the same.
eq- Any two distinct Lisp objects are different as keys.
equal- Two Lisp objects are the same, as keys, if they are equal according to
equal.You can use
define-hash-table-test(see Defining Hash) to define additional possibilities for test.:weaknessweak- The weakness of a hash table specifies whether the presence of a key or value in the hash table preserves it from garbage collection.
The value, weak, must be one of
nil,key,value,key-or-value,key-and-value, ortwhich is an alias forkey-and-value. If weak iskeythen the hash table does not prevent its keys from being collected as garbage (if they are not referenced anywhere else); if a particular key does get collected, the corresponding association is removed from the hash table.If weak is
value, then the hash table does not prevent values from being collected as garbage (if they are not referenced anywhere else); if a particular value does get collected, the corresponding association is removed from the hash table.If weak is
key-and-valueort, both the key and the value must be live in order to preserve the association. Thus, the hash table does not protect either keys or values from garbage collection; if either one is collected as garbage, that removes the association.If weak is
key-or-value, either the key or the value can preserve the association. Thus, associations are removed from the hash table when both their key and value would be collected as garbage (if not for references from weak hash tables).The default for weak is
nil, so that all keys and values referenced in the hash table are preserved from garbage collection.:sizesize- This specifies a hint for how many associations you plan to store in the hash table. If you know the approximate number, you can make things a little more efficient by specifying it this way. If you specify too small a size, the hash table will grow automatically when necessary, but doing that takes some extra time.
The default size is 65.
:rehash-sizerehash-size- When you add an association to a hash table and the table is full, it grows automatically. This value specifies how to make the hash table larger, at that time.
If rehash-size is an integer, it should be positive, and the hash table grows by adding that much to the nominal size. If rehash-size is floating point, it had better be greater than 1, and the hash table grows by multiplying the old size by that number.
The default value is 1.5.
:rehash-thresholdthreshold- This specifies the criterion for when the hash table is full (so it should be made larger). The value, threshold, should be a positive floating-point number, no greater than 1. The hash table is full whenever the actual number of entries exceeds this fraction of the nominal size. The default for threshold is 0.8.
You can also create a new hash table using the printed representation
for hash tables. The Lisp reader can read this printed
representation, provided each element in the specified hash table has
a valid read syntax (see Printed Representation). For instance,
the following specifies a new hash table containing the keys
key1 and key2 (both symbols) associated with val1
(a symbol) and 300 (a number) respectively.
#s(hash-table size 30 data (key1 val1 key2 300))
The printed representation for a hash table consists of `#s'
followed by a list beginning with `hash-table'. The rest of the
list should consist of zero or more property-value pairs specifying
the hash table's properties and initial contents. The properties and
values are read literally. Valid property names are size,
test, weakness, rehash-size,
rehash-threshold, and data. The data property
should be a list of key-value pairs for the initial contents; the
other properties have the same meanings as the matching
make-hash-table keywords (:size, :test, etc.),
described above.
Note that you cannot specify a hash table whose initial contents include objects that have no read syntax, such as buffers and frames. Such objects may be added to the hash table after it is created.
This section describes the functions for accessing and storing associations in a hash table. In general, any Lisp object can be used as a hash key, unless the comparison method imposes limits. Any Lisp object can also be used as the value.
This function looks up key in table, and returns its associated value—or default, if key has no association in table.
This function enters an association for key in table, with value value. If key already has an association in table, value replaces the old associated value.
This function removes the association for key from table, if there is one. If key has no association,
remhashdoes nothing.Common Lisp note: In Common Lisp,
remhashreturns non-nilif it actually removed an association andnilotherwise. In Emacs Lisp,remhashalways returnsnil.
This function removes all the associations from hash table table, so that it becomes empty. This is also called clearing the hash table.
Common Lisp note: In Common Lisp,
clrhashreturns the empty table. In Emacs Lisp, it returnsnil.
This function calls function once for each of the associations in table. The function function should accept two arguments—a key listed in table, and its associated value.
maphashreturnsnil.
You can define new methods of key lookup by means of
define-hash-table-test. In order to use this feature, you need
to understand how hash tables work, and what a hash code means.
You can think of a hash table conceptually as a large array of many
slots, each capable of holding one association. To look up a key,
gethash first computes an integer, the hash code, from the key.
It reduces this integer modulo the length of the array, to produce an
index in the array. Then it looks in that slot, and if necessary in
other nearby slots, to see if it has found the key being sought.
Thus, to define a new method of key lookup, you need to specify both a function to compute the hash code from a key, and a function to compare two keys directly.
This function defines a new hash table test, named name.
After defining name in this way, you can use it as the test argument in
make-hash-table. When you do that, the hash table will use test-fn to compare key values, and hash-fn to compute a hash code from a key value.The function test-fn should accept two arguments, two keys, and return non-
nilif they are considered the same.The function hash-fn should accept one argument, a key, and return an integer that is the hash code of that key. For good results, the function should use the whole range of integers for hash codes, including negative integers.
The specified functions are stored in the property list of name under the property
hash-table-test; the property value's form is(test-fn hash-fn).
This function returns a hash code for Lisp object obj. This is an integer which reflects the contents of obj and the other Lisp objects it points to.
If two objects obj1 and obj2 are equal, then
(sxhashobj1)and(sxhashobj2)are the same integer.If the two objects are not equal, the values returned by
sxhashare usually different, but not always; once in a rare while, by luck, you will encounter two distinct-looking objects that give the same result fromsxhash.
This example creates a hash table whose keys are strings that are compared case-insensitively.
(defun case-fold-string= (a b)
(eq t (compare-strings a nil nil b nil nil t)))
(defun case-fold-string-hash (a)
(sxhash (upcase a)))
(define-hash-table-test 'case-fold
'case-fold-string= 'case-fold-string-hash)
(make-hash-table :test 'case-fold)
Here is how you could define a hash table test equivalent to the
predefined test value equal. The keys can be any Lisp object,
and equal-looking objects are considered the same key.
(define-hash-table-test 'contents-hash 'equal 'sxhash)
(make-hash-table :test 'contents-hash)
Here are some other functions for working with hash tables.
This function creates and returns a copy of table. Only the table itself is copied—the keys and values are shared.
This returns the test value that was given when table was created, to specify how to hash and compare keys. See
make-hash-table(see Creating Hash).
This function returns the weak value that was specified for hash table table.
A symbol is an object with a unique name. This chapter describes symbols, their components, their property lists, and how they are created and interned. Separate chapters describe the use of symbols as variables and as function names; see Variables, and Functions. For the precise read syntax for symbols, see Symbol Type.
You can test whether an arbitrary Lisp object is a symbol with
symbolp:
Each symbol has four components (or “cells”), each of which references another object:
The print name cell always holds a string, and cannot be changed. Each of the other three cells can be set to any Lisp object.
The print name cell holds the string that is the name of a symbol.
Since symbols are represented textually by their names, it is
important not to have two symbols with the same name. The Lisp reader
ensures this: every time it reads a symbol, it looks for an existing
symbol with the specified name before it creates a new one. To get a
symbol's name, use the function symbol-name (see Creating Symbols).
The value cell holds a symbol's value as a variable, which is what
you get if the symbol itself is evaluated as a Lisp expression.
See Variables, for details about how values are set and retrieved,
including complications such as local bindings and scoping
rules. Most symbols can have any Lisp object as a value, but certain
special symbols have values that cannot be changed; these include
nil and t, and any symbol whose name starts with
`:' (those are called keywords). See Constant Variables.
The function cell holds a symbol's function definition. Often, we
refer to “the function foo” when we really mean the function
stored in the function cell of foo; we make the distinction
explicit only when necessary. Typically, the function cell is used to
hold a function (see Functions) or a macro (see Macros).
However, it can also be used to hold a symbol (see Function Indirection), keyboard macro (see Keyboard Macros), keymap
(see Keymaps), or autoload object (see Autoloading). To get
the contents of a symbol's function cell, use the function
symbol-function (see Function Cells).
The property list cell normally should hold a correctly formatted
property list. To get a symbol's property list, use the function
symbol-plist. See Symbol Properties.
The function cell or the value cell may be void, which means
that the cell does not reference any object. (This is not the same
thing as holding the symbol void, nor the same as holding the
symbol nil.) Examining a function or value cell that is void
results in an error, such as `Symbol's value as variable is void'.
Because each symbol has separate value and function cells, variables
names and function names do not conflict. For example, the symbol
buffer-file-name has a value (the name of the file being
visited in the current buffer) as well as a function definition (a
primitive function that returns the name of the file):
buffer-file-name
=> "/gnu/elisp/symbols.texi"
(symbol-function 'buffer-file-name)
=> #<subr buffer-file-name>
A definition is a special kind of Lisp expression that announces your intention to use a symbol in a particular way. It typically specifies a value or meaning for the symbol for one kind of use, plus documentation for its meaning when used in this way. Thus, when you define a symbol as a variable, you can supply an initial value for the variable, plus documentation for the variable.
defvar and defconst are special forms that define a
symbol as a global variable—a variable that can be accessed at
any point in a Lisp program. See Variables, for details about
variables. To define a customizable variable, use the
defcustom macro, which also calls defvar as a subroutine
(see Customization).
In principle, you can assign a variable value to any symbol with
setq, whether not it has first been defined as a variable.
However, you ought to write a variable definition for each global
variable that you want to use; otherwise, your Lisp program may not
act correctly if it is evaluated with lexical scoping enabled
(see Variable Scoping).
defun defines a symbol as a function, creating a lambda
expression and storing it in the function cell of the symbol. This
lambda expression thus becomes the function definition of the symbol.
(The term “function definition”, meaning the contents of the function
cell, is derived from the idea that defun gives the symbol its
definition as a function.) defsubst and defalias are two
other ways of defining a function. See Functions.
defmacro defines a symbol as a macro. It creates a macro
object and stores it in the function cell of the symbol. Note that a
given symbol can be a macro or a function, but not both at once, because
both macro and function definitions are kept in the function cell, and
that cell can hold only one Lisp object at any given time.
See Macros.
As previously noted, Emacs Lisp allows the same symbol to be defined
both as a variable (e.g., with defvar) and as a function or
macro (e.g., with defun). Such definitions do not conflict.
These definition also act as guides for programming tools. For example, the C-h f and C-h v commands create help buffers containing links to the relevant variable, function, or macro definitions. See Name Help.
To understand how symbols are created in GNU Emacs Lisp, you must know how Lisp reads them. Lisp must ensure that it finds the same symbol every time it reads the same set of characters. Failure to do so would cause complete confusion.
When the Lisp reader encounters a symbol, it reads all the characters of the name. Then it hashes those characters to find an index in a table called an obarray. Hashing is an efficient method of looking something up. For example, instead of searching a telephone book cover to cover when looking up Jan Jones, you start with the J's and go from there. That is a simple version of hashing. Each element of the obarray is a bucket which holds all the symbols with a given hash code; to look for a given name, it is sufficient to look through all the symbols in the bucket for that name's hash code. (The same idea is used for general Emacs hash tables, but they are a different data type; see Hash Tables.)
If a symbol with the desired name is found, the reader uses that symbol. If the obarray does not contain a symbol with that name, the reader makes a new symbol and adds it to the obarray. Finding or adding a symbol with a certain name is called interning it, and the symbol is then called an interned symbol.
Interning ensures that each obarray has just one symbol with any particular name. Other like-named symbols may exist, but not in the same obarray. Thus, the reader gets the same symbols for the same names, as long as you keep reading with the same obarray.
Interning usually happens automatically in the reader, but sometimes other programs need to do it. For example, after the M-x command obtains the command name as a string using the minibuffer, it then interns the string, to get the interned symbol with that name.
No obarray contains all symbols; in fact, some symbols are not in any obarray. They are called uninterned symbols. An uninterned symbol has the same four cells as other symbols; however, the only way to gain access to it is by finding it in some other object or as the value of a variable.
Creating an uninterned symbol is useful in generating Lisp code, because an uninterned symbol used as a variable in the code you generate cannot clash with any variables used in other Lisp programs.
In Emacs Lisp, an obarray is actually a vector. Each element of the
vector is a bucket; its value is either an interned symbol whose name
hashes to that bucket, or 0 if the bucket is empty. Each interned
symbol has an internal link (invisible to the user) to the next symbol
in the bucket. Because these links are invisible, there is no way to
find all the symbols in an obarray except using mapatoms (below).
The order of symbols in a bucket is not significant.
In an empty obarray, every element is 0, so you can create an obarray
with (make-vector length 0). This is the only
valid way to create an obarray. Prime numbers as lengths tend
to result in good hashing; lengths one less than a power of two are also
good.
Do not try to put symbols in an obarray yourself. This does
not work—only intern can enter a symbol in an obarray properly.
Common Lisp note: Unlike Common Lisp, Emacs Lisp does not provide for interning a single symbol in several obarrays.
Most of the functions below take a name and sometimes an obarray as
arguments. A wrong-type-argument error is signaled if the name
is not a string, or if the obarray is not a vector.
This function returns the string that is symbol's name. For example:
(symbol-name 'foo) => "foo"Warning: Changing the string by substituting characters does change the name of the symbol, but fails to update the obarray, so don't do it!
This function returns a newly-allocated, uninterned symbol whose name is name (which must be a string). Its value and function definition are void, and its property list is
nil. In the example below, the value ofsymis noteqtofoobecause it is a distinct uninterned symbol whose name is also `foo'.(setq sym (make-symbol "foo")) => foo (eq sym 'foo) => nil
This function returns the interned symbol whose name is name. If there is no such symbol in the obarray obarray,
interncreates a new one, adds it to the obarray, and returns it. If obarray is omitted, the value of the global variableobarrayis used.(setq sym (intern "foo")) => foo (eq sym 'foo) => t (setq sym1 (intern "foo" other-obarray)) => foo (eq sym1 'foo) => nil
Common Lisp note: In Common Lisp, you can intern an existing symbol
in an obarray. In Emacs Lisp, you cannot do this, because the argument
to intern must be a string, not a symbol.
This function returns the symbol in obarray whose name is name, or
nilif obarray has no symbol with that name. Therefore, you can useintern-softto test whether a symbol with a given name is already interned. If obarray is omitted, the value of the global variableobarrayis used.The argument name may also be a symbol; in that case, the function returns name if name is interned in the specified obarray, and otherwise
nil.(intern-soft "frazzle") ; No such symbol exists. => nil (make-symbol "frazzle") ; Create an uninterned one. => frazzle (intern-soft "frazzle") ; That one cannot be found. => nil (setq sym (intern "frazzle")) ; Create an interned one. => frazzle (intern-soft "frazzle") ; That one can be found! => frazzle (eq sym 'frazzle) ; And it is the same one. => t
This function calls function once with each symbol in the obarray obarray. Then it returns
nil. If obarray is omitted, it defaults to the value ofobarray, the standard obarray for ordinary symbols.(setq count 0) => 0 (defun count-syms (s) (setq count (1+ count))) => count-syms (mapatoms 'count-syms) => nil count => 1871See
documentationin Accessing Documentation, for another example usingmapatoms.
This function deletes symbol from the obarray obarray. If
symbolis not actually in the obarray,uninterndoes nothing. If obarray isnil, the current obarray is used.If you provide a string instead of a symbol as symbol, it stands for a symbol name. Then
uninterndeletes the symbol (if any) in the obarray which has that name. If there is no such symbol,uninterndoes nothing.If
uninterndoes delete a symbol, it returnst. Otherwise it returnsnil.
A symbol may possess any number of symbol properties, which
can be used to record miscellaneous information about the symbol. For
example, when a symbol has a risky-local-variable property with
a non-nil value, that means the variable which the symbol names
is a risky file-local variable (see File Local Variables).
Each symbol's properties and property values are stored in the symbol's property list cell (see Symbol Components), in the form of a property list (see Property Lists).
The following functions can be used to access symbol properties.
This function returns the value of the property named property in symbol's property list. If there is no such property, it returns
nil. Thus, there is no distinction between a value ofniland the absence of the property.The name property is compared with the existing property names using
eq, so any object is a legitimate property.See
putfor an example.
This function puts value onto symbol's property list under the property name property, replacing any previous property value. The
putfunction returns value.(put 'fly 'verb 'transitive) =>'transitive (put 'fly 'noun '(a buzzing little bug)) => (a buzzing little bug) (get 'fly 'verb) => transitive (symbol-plist 'fly) => (verb transitive noun (a buzzing little bug))
This function sets symbol's property list to plist. Normally, plist should be a well-formed property list, but this is not enforced. The return value is plist.
(setplist 'foo '(a 1 b (2 3) c nil)) => (a 1 b (2 3) c nil) (symbol-plist 'foo) => (a 1 b (2 3) c nil)For symbols in special obarrays, which are not used for ordinary purposes, it may make sense to use the property list cell in a nonstandard fashion; in fact, the abbrev mechanism does so (see Abbrevs).
You could define
putin terms ofsetplistandplist-put, as follows:(defun put (symbol prop value) (setplist symbol (plist-put (symbol-plist symbol) prop value)))
This function is identical to
get, except that if symbol is the name of a function alias, it looks in the property list of the symbol naming the actual function. See Defining Functions. If the optional argument autoload is non-nil, and symbol is auto-loaded, this function will try to autoload it, since autoloading might set property of symbol. If autoload is the symbolmacro, only try autoloading if symbol is an auto-loaded macro.
This function sets property of function to value. function should be a symbol. This function is preferred to calling
putfor setting properties of a function, because it will allow us some day to implement remapping of old properties to new ones.
Here, we list the symbol properties which are used for special purposes in Emacs. In the following table, whenever we say “the named function”, that means the function whose name is the relevant symbol; similarly for “the named variable” etc.
:advertised-bindingchar-table-extra-slotsnil, specifies the number of extra slots in
the named char-table type. See Char-Tables.
customized-faceface-defface-specsaved-facetheme-facedefface and related functions. See Defining Faces.
customized-valuesaved-valuestandard-valuetheme-valuedefcustom and
related functions. See Variable Definitions.
disablednil, the named function is disabled as a
command. See Disabling Commands.
face-documentationdefface. See Defining Faces.
history-lengthnil, specifies the maximum minibuffer history
length for the named history list variable. See Minibuffer History.
interactive-forminteractive special
form instead. See Interactive Call.
menu-enablemode-classspecial, the named major mode is special.
See Major Mode Conventions.
permanent-localnil, the named variable is a buffer-local
variable whose value should not be reset when changing major modes.
See Creating Buffer-Local.
permanent-local-hooknil, the named function should not be
deleted from the local value of a hook variable when changing major
modes. See Setting Hooks.
purenil, the named function is considered to be
side-effect free. Calls with constant arguments can be evaluated at
compile time. This may shift run time errors to compile time.
risky-local-variablenil, the named variable is considered risky
as a file-local variable. See File Local Variables.
safe-functionnil, the named function is considered
generally safe for evaluation. See Function Safety.
safe-local-eval-functionnil, the named function is safe to call in
file-local evaluation forms. See File Local Variables.
safe-local-variableside-effect-freenil value indicates that the named function is free of
side-effects, for determining function safety (see Function Safety) as well as for byte compiler optimizations. Do not set it.
variable-documentationnil, this specifies the named variable's documentation
string. This is set automatically by defvar and related
functions. See Defining Faces.
The evaluation of expressions in Emacs Lisp is performed by the
Lisp interpreter—a program that receives a Lisp object as input
and computes its value as an expression. How it does this depends
on the data type of the object, according to rules described in this
chapter. The interpreter runs automatically to evaluate portions of
your program, but can also be called explicitly via the Lisp primitive
function eval.
The Lisp interpreter, or evaluator, is the part of Emacs that computes the value of an expression that is given to it. When a function written in Lisp is called, the evaluator computes the value of the function by evaluating the expressions in the function body. Thus, running any Lisp program really means running the Lisp interpreter.
A Lisp object that is intended for evaluation is called a form or expression4. The fact that forms are data objects and not merely text is one of the fundamental differences between Lisp-like languages and typical programming languages. Any object can be evaluated, but in practice only numbers, symbols, lists and strings are evaluated very often.
In subsequent sections, we will describe the details of what evaluation means for each kind of form.
It is very common to read a Lisp form and then evaluate the form,
but reading and evaluation are separate activities, and either can be
performed alone. Reading per se does not evaluate anything; it
converts the printed representation of a Lisp object to the object
itself. It is up to the caller of read to specify whether this
object is a form to be evaluated, or serves some entirely different
purpose. See Input Functions.
Evaluation is a recursive process, and evaluating a form often
involves evaluating parts within that form. For instance, when you
evaluate a function call form such as (car x), Emacs
first evaluates the argument (the subform x). After evaluating
the argument, Emacs executes the function (car), and if
the function is written in Lisp, execution works by evaluating the
body of the function (in this example, however, car is
not a Lisp function; it is a primitive function implemented in C).
See Functions, for more information about functions and function
calls.
Evaluation takes place in a context called the environment, which consists of the current values and bindings of all Lisp variables (see Variables).5 Whenever a form refers to a variable without creating a new binding for it, the variable evaluates to the value given by the current environment. Evaluating a form may also temporarily alter the environment by binding variables (see Local Variables).
Evaluating a form may also make changes that persist; these changes
are called side effects. An example of a form that produces a
side effect is (setq foo 1).
Do not confuse evaluation with command key interpretation. The
editor command loop translates keyboard input into a command (an
interactively callable function) using the active keymaps, and then
uses call-interactively to execute that command. Executing the
command usually involves evaluation, if the command is written in
Lisp; however, this step is not considered a part of command key
interpretation. See Command Loop.
A Lisp object that is intended to be evaluated is called a form (or an expression). How Emacs evaluates a form depends on its data type. Emacs has three different kinds of form that are evaluated differently: symbols, lists, and all other types. This section describes all three kinds, one by one, starting with the other types, which are self-evaluating forms.
A self-evaluating form is any form that is not a list or
symbol. Self-evaluating forms evaluate to themselves: the result of
evaluation is the same object that was evaluated. Thus, the number 25
evaluates to 25, and the string "foo" evaluates to the string
"foo". Likewise, evaluating a vector does not cause evaluation
of the elements of the vector—it returns the same vector with its
contents unchanged.
'123 ; A number, shown without evaluation. => 123 123 ; Evaluated as usual---result is the same. => 123 (eval '123) ; Evaluated "by hand"---result is the same. => 123 (eval (eval '123)) ; Evaluating twice changes nothing. => 123
It is common to write numbers, characters, strings, and even vectors in Lisp code, taking advantage of the fact that they self-evaluate. However, it is quite unusual to do this for types that lack a read syntax, because there's no way to write them textually. It is possible to construct Lisp expressions containing these types by means of a Lisp program. Here is an example:
;; Build an expression containing a buffer object. (setq print-exp (list 'print (current-buffer))) => (print #<buffer eval.texi>) ;; Evaluate it. (eval print-exp) -| #<buffer eval.texi> => #<buffer eval.texi>
When a symbol is evaluated, it is treated as a variable. The result is the variable's value, if it has one. If the symbol has no value as a variable, the Lisp interpreter signals an error. For more information on the use of variables, see Variables.
In the following example, we set the value of a symbol with
setq. Then we evaluate the symbol, and get back the value that
setq stored.
(setq a 123)
=> 123
(eval 'a)
=> 123
a
=> 123
The symbols nil and t are treated specially, so that the
value of nil is always nil, and the value of t is
always t; you cannot set or bind them to any other values. Thus,
these two symbols act like self-evaluating forms, even though
eval treats them like any other symbol. A symbol whose name
starts with `:' also self-evaluates in the same way; likewise,
its value ordinarily cannot be changed. See Constant Variables.
A form that is a nonempty list is either a function call, a macro call, or a special form, according to its first element. These three kinds of forms are evaluated in different ways, described below. The remaining list elements constitute the arguments for the function, macro, or special form.
The first step in evaluating a nonempty list is to examine its first element. This element alone determines what kind of form the list is and how the rest of the list is to be processed. The first element is not evaluated, as it would be in some Lisp dialects such as Scheme.
If the first element of the list is a symbol then evaluation examines the symbol's function cell, and uses its contents instead of the original symbol. If the contents are another symbol, this process, called symbol function indirection, is repeated until it obtains a non-symbol. See Function Names, for more information about symbol function indirection.
One possible consequence of this process is an infinite loop, in the event that a symbol's function cell refers to the same symbol. Otherwise, we eventually obtain a non-symbol, which ought to be a function or other suitable object.
More precisely, we should now have a Lisp function (a lambda
expression), a byte-code function, a primitive function, a Lisp macro,
a special form, or an autoload object. Each of these types is a case
described in one of the following sections. If the object is not one
of these types, Emacs signals an invalid-function error.
The following example illustrates the symbol indirection process.
We use fset to set the function cell of a symbol and
symbol-function to get the function cell contents
(see Function Cells). Specifically, we store the symbol
car into the function cell of first, and the symbol
first into the function cell of erste.
;; Build this function cell linkage:
;; ------------- ----- ------- -------
;; | #<subr car> | <-- | car | <-- | first | <-- | erste |
;; ------------- ----- ------- -------
(symbol-function 'car)
=> #<subr car>
(fset 'first 'car)
=> car
(fset 'erste 'first)
=> first
(erste '(1 2 3)) ; Call the function referenced by erste.
=> 1
By contrast, the following example calls a function without any symbol function indirection, because the first element is an anonymous Lisp function, not a symbol.
((lambda (arg) (erste arg))
'(1 2 3))
=> 1
Executing the function itself evaluates its body; this does involve
symbol function indirection when calling erste.
This form is rarely used and is now deprecated. Instead, you should write it as:
(funcall (lambda (arg) (erste arg))
'(1 2 3))
or just
(let ((arg '(1 2 3))) (erste arg))
The built-in function indirect-function provides an easy way to
perform symbol function indirection explicitly.
This function returns the meaning of function as a function. If function is a symbol, then it finds function's function definition and starts over with that value. If function is not a symbol, then it returns function itself.
This function returns
nilif the final symbol is unbound. It signals acyclic-function-indirectionerror if there is a loop in the chain of symbols.The optional argument noerror is obsolete, kept for backward compatibility, and has no effect.
Here is how you could define
indirect-functionin Lisp:(defun indirect-function (function) (if (symbolp function) (indirect-function (symbol-function function)) function))
If the first element of a list being evaluated is a Lisp function
object, byte-code object or primitive function object, then that list is
a function call. For example, here is a call to the function
+:
(+ 1 x)
The first step in evaluating a function call is to evaluate the
remaining elements of the list from left to right. The results are the
actual argument values, one value for each list element. The next step
is to call the function with this list of arguments, effectively using
the function apply (see Calling Functions). If the function
is written in Lisp, the arguments are used to bind the argument
variables of the function (see Lambda Expressions); then the forms
in the function body are evaluated in order, and the value of the last
body form becomes the value of the function call.
If the first element of a list being evaluated is a macro object, then the list is a macro call. When a macro call is evaluated, the elements of the rest of the list are not initially evaluated. Instead, these elements themselves are used as the arguments of the macro. The macro definition computes a replacement form, called the expansion of the macro, to be evaluated in place of the original form. The expansion may be any sort of form: a self-evaluating constant, a symbol, or a list. If the expansion is itself a macro call, this process of expansion repeats until some other sort of form results.
Ordinary evaluation of a macro call finishes by evaluating the expansion. However, the macro expansion is not necessarily evaluated right away, or at all, because other programs also expand macro calls, and they may or may not evaluate the expansions.
Normally, the argument expressions are not evaluated as part of computing the macro expansion, but instead appear as part of the expansion, so they are computed when the expansion is evaluated.
For example, given a macro defined as follows:
(defmacro cadr (x)
(list 'car (list 'cdr x)))
an expression such as (cadr (assq 'handler list)) is a macro
call, and its expansion is:
(car (cdr (assq 'handler list)))
Note that the argument (assq 'handler list) appears in the
expansion.
See Macros, for a complete description of Emacs Lisp macros.
A special form is a primitive function specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings—things which functions cannot do.
Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.
If an expression's first symbol is that of a special form, the
expression should follow the rules of that special form; otherwise,
Emacs's behavior is not well-defined (though it will not crash). For
example, ((lambda (x) x . 3) 4) contains a subexpression that
begins with lambda but is not a well-formed lambda
expression, so Emacs may signal an error, or may return 3 or 4 or
nil, or may behave in other ways.
This predicate tests whether its argument is a special form, and returns
tif so,nilotherwise.
Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described.
andcatchcondcondition-casedefconstdefvarfunctionifinteractivelambdaletlet*orprog1prog2prognquotesave-current-buffersave-excursionsave-restrictionsetqsetq-defaulttrack-mouseunwind-protectwhileCommon Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp.setq,if, andcatchare special forms in both Emacs Lisp and Common Lisp.save-excursionis a special form in Emacs Lisp, but doesn't exist in Common Lisp.throwis a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn't have multiple values).
The autoload feature allows you to call a function or macro whose function definition has not yet been loaded into Emacs. It specifies which file contains the definition. When an autoload object appears as a symbol's function definition, calling that symbol as a function automatically loads the specified file; then it calls the real definition loaded from that file. The way to arrange for an autoload object to appear as a symbol's function definition is described in Autoload.
The special form quote returns its single argument, as written,
without evaluating it. This provides a way to include constant symbols
and lists, which are not self-evaluating objects, in a program. (It is
not necessary to quote self-evaluating objects such as numbers, strings,
and vectors.)
Because quote is used so often in programs, Lisp provides a
convenient read syntax for it. An apostrophe character (`'')
followed by a Lisp object (in read syntax) expands to a list whose first
element is quote, and whose second element is the object. Thus,
the read syntax 'x is an abbreviation for (quote x).
Here are some examples of expressions that use quote:
(quote (+ 1 2))
=> (+ 1 2)
(quote foo)
=> foo
'foo
=> foo
''foo
=> (quote foo)
'(quote foo)
=> (quote foo)
['foo]
=> [(quote foo)]
Other quoting constructs include function (see Anonymous Functions), which causes an anonymous lambda expression written in Lisp
to be compiled, and ``' (see Backquote), which is used to quote
only part of a list, while computing and substituting other parts.
Backquote constructs allow you to quote a list, but
selectively evaluate elements of that list. In the simplest case, it
is identical to the special form quote
(described in the previous section; see Quoting).
For example, these two forms yield identical results:
`(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
'(a list of (+ 2 3) elements)
=> (a list of (+ 2 3) elements)
The special marker `,' inside of the argument to backquote indicates a value that isn't constant. The Emacs Lisp evaluator evaluates the argument of `,', and puts the value in the list structure:
`(a list of ,(+ 2 3) elements)
=> (a list of 5 elements)
Substitution with `,' is allowed at deeper levels of the list structure also. For example:
`(1 2 (3 ,(+ 4 5)))
=> (1 2 (3 9))
You can also splice an evaluated value into the resulting list, using the special marker `,@'. The elements of the spliced list become elements at the same level as the other elements of the resulting list. The equivalent code without using ``' is often unreadable. Here are some examples:
(setq some-list '(2 3))
=> (2 3)
(cons 1 (append some-list '(4) some-list))
=> (1 2 3 4 2 3)
`(1 ,@some-list 4 ,@some-list)
=> (1 2 3 4 2 3)
(setq list '(hack foo bar))
=> (hack foo bar)
(cons 'use
(cons 'the
(cons 'words (append (cdr list) '(as elements)))))
=> (use the words foo bar as elements)
`(use the words ,@(cdr list) as elements)
=> (use the words foo bar as elements)
Most often, forms are evaluated automatically, by virtue of their
occurrence in a program being run. On rare occasions, you may need to
write code that evaluates a form that is computed at run time, such as
after reading a form from text being edited or getting one from a
property list. On these occasions, use the eval function.
Often eval is not needed and something else should be used instead.
For example, to get the value of a variable, while eval works,
symbol-value is preferable; or rather than store expressions
in a property list that then need to go through eval, it is better to
store functions instead that are then passed to funcall.
The functions and variables described in this section evaluate forms, specify limits to the evaluation process, or record recently returned values. Loading a file also does evaluation (see Loading).
It is generally cleaner and more flexible to store a function in a
data structure, and call it with funcall or apply, than
to store an expression in the data structure and evaluate it. Using
functions provides the ability to pass information to them as
arguments.
This is the basic function for evaluating an expression. It evaluates form in the current environment, and returns the result. The type of the form object determines how it is evaluated. See Forms.
The argument lexical specifies the scoping rule for local variables (see Variable Scoping). If it is omitted or
nil, that means to evaluate form using the default dynamic scoping rule. If it ist, that means to use the lexical scoping rule. The value of lexical can also be a non-empty alist specifying a particular lexical environment for lexical bindings; however, this feature is only useful for specialized purposes, such as in Emacs Lisp debuggers. See Lexical Binding.Since
evalis a function, the argument expression that appears in a call toevalis evaluated twice: once as preparation beforeevalis called, and again by theevalfunction itself. Here is an example:(setq foo 'bar) => bar (setq bar 'baz) => baz ;; Hereevalreceives argumentfoo(eval 'foo) => bar ;; Hereevalreceives argumentbar, which is the value offoo(eval foo) => bazThe number of currently active calls to
evalis limited tomax-lisp-eval-depth(see below).
This function evaluates the forms in the current buffer in the region defined by the positions start and end. It reads forms from the region and calls
evalon them until the end of the region is reached, or until an error is signaled and not handled.By default,
eval-regiondoes not produce any output. However, if stream is non-nil, any output produced by output functions (see Output Functions), as well as the values that result from evaluating the expressions in the region are printed using stream. See Output Streams.If read-function is non-
nil, it should be a function, which is used instead ofreadto read expressions one by one. This function is called with one argument, the stream for reading input. You can also use the variableload-read-function(see How Programs Do Loading) to specify this function, but it is more robust to use the read-function argument.
eval-regiondoes not move point. It always returnsnil.
This is similar to
eval-region, but the arguments provide different optional features.eval-bufferoperates on the entire accessible portion of buffer buffer-or-name (see Narrowing). buffer-or-name can be a buffer, a buffer name (a string), ornil(or omitted), which means to use the current buffer. stream is used as ineval-region, unless stream isniland print non-nil. In that case, values that result from evaluating the expressions are still discarded, but the output of the output functions is printed in the echo area. filename is the file name to use forload-history(see Unloading), and defaults tobuffer-file-name(see Buffer File Name). If unibyte is non-nil,readconverts strings to unibyte whenever possible.
This variable defines the maximum depth allowed in calls to
eval,apply, andfuncallbefore an error is signaled (with error message"Lisp nesting exceeds max-lisp-eval-depth").This limit, with the associated error when it is exceeded, is one way Emacs Lisp avoids infinite recursion on an ill-defined function. If you increase the value of
max-lisp-eval-depthtoo much, such code can cause stack overflow instead. On some systems, this overflow can be handled. In that case, normal Lisp evaluation is interrupted and control is transferred back to the top level command loop (top-level). Note that there is no way to enter Emacs Lisp debugger in this situation. See Error Debugging.The depth limit counts internal uses of
eval,apply, andfuncall, such as for calling the functions mentioned in Lisp expressions, and recursive evaluation of function call arguments and function body forms, as well as explicit calls in Lisp code.The default value of this variable is 400. If you set it to a value less than 100, Lisp will reset it to 100 if the given value is reached. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
max-specpdl-sizeprovides another limit on nesting. See Local Variables.
The value of this variable is a list of the values returned by all the expressions that were read, evaluated, and printed from buffers (including the minibuffer) by the standard Emacs commands which do this. (Note that this does not include evaluation in *ielm* buffers, nor evaluation using C-j, C-x C-e, and similar evaluation commands in
lisp-interaction-mode.) The elements are ordered most recent first.(setq x 1) => 1 (list 'A (1+ 2) auto-save-default) => (A 3 t) values => ((A 3 t) 1 ...)This variable is useful for referring back to values of forms recently evaluated. It is generally a bad idea to print the value of
valuesitself, since this may be very long. Instead, examine particular elements, like this:;; Refer to the most recent evaluation result. (nth 0 values) => (A 3 t) ;; That put a new element on, ;; so all elements move back one. (nth 1 values) => (A 3 t) ;; This gets the element that was next-to-most-recent ;; before this example. (nth 3 values) => 1
A Lisp program consists of a set of expressions, or forms (see Forms). We control the order of execution of these forms by enclosing them in control structures. Control structures are special forms which control when, whether, or how many times to execute the forms they contain.
The simplest order of execution is sequential execution: first form a, then form b, and so on. This is what happens when you write several forms in succession in the body of a function, or at top level in a file of Lisp code—the forms are executed in the order written. We call this textual order. For example, if a function body consists of two forms a and b, evaluation of the function evaluates first a and then b. The result of evaluating b becomes the value of the function.
Explicit control structures make possible an order of execution other than sequential.
Emacs Lisp provides several kinds of control structure, including other varieties of sequencing, conditionals, iteration, and (controlled) jumps—all discussed below. The built-in control structures are special forms since their subforms are not necessarily evaluated or not evaluated sequentially. You can use macros to define your own control structure constructs (see Macros).
Evaluating forms in the order they appear is the most common way
control passes from one form to another. In some contexts, such as in a
function body, this happens automatically. Elsewhere you must use a
control structure construct to do this: progn, the simplest
control construct of Lisp.
A progn special form looks like this:
(progn a b c ...)
and it says to execute the forms a, b, c, and so on, in
that order. These forms are called the body of the progn form.
The value of the last form in the body becomes the value of the entire
progn. (progn) returns nil.
In the early days of Lisp, progn was the only way to execute
two or more forms in succession and use the value of the last of them.
But programmers found they often needed to use a progn in the
body of a function, where (at that time) only one form was allowed. So
the body of a function was made into an implicit progn:
several forms are allowed just as in the body of an actual progn.
Many other control structures likewise contain an implicit progn.
As a result, progn is not used as much as it was many years ago.
It is needed now most often inside an unwind-protect, and,
or, or in the then-part of an if.
This special form evaluates all of the forms, in textual order, returning the result of the final form.
(progn (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The third form"
Two other constructs likewise evaluate a series of forms but return different values:
This special form evaluates form1 and all of the forms, in textual order, returning the result of form1.
(prog1 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The first form"Here is a way to remove the first element from a list in the variable
x, then return the value of that former element:(prog1 (car x) (setq x (cdr x)))
This special form evaluates form1, form2, and all of the following forms, in textual order, returning the result of form2.
(prog2 (print "The first form") (print "The second form") (print "The third form")) -| "The first form" -| "The second form" -| "The third form" => "The second form"
Conditional control structures choose among alternatives. Emacs Lisp
has four conditional forms: if, which is much the same as in
other languages; when and unless, which are variants of
if; and cond, which is a generalized case statement.
ifchooses between the then-form and the else-forms based on the value of condition. If the evaluated condition is non-nil, then-form is evaluated and the result returned. Otherwise, the else-forms are evaluated in textual order, and the value of the last one is returned. (The else part ofifis an example of an implicitprogn. See Sequencing.)If condition has the value
nil, and no else-forms are given,ifreturnsnil.
ifis a special form because the branch that is not selected is never evaluated—it is ignored. Thus, in this example,trueis not printed because(if nil (print 'true) 'very-false) => very-false
This is a variant of
ifwhere there are no else-forms, and possibly several then-forms. In particular,(when condition a b c)is entirely equivalent to
(if condition (progn a b c) nil)
This is a variant of
ifwhere there is no then-form:(unless condition a b c)is entirely equivalent to
(if condition nil a b c)
condchooses among an arbitrary number of alternatives. Each clause in thecondmust be a list. The car of this list is the condition; the remaining elements, if any, the body-forms. Thus, a clause looks like this:(condition body-forms...)
condtries the clauses in textual order, by evaluating the condition of each clause. If the value of condition is non-nil, the clause succeeds; thencondevaluates its body-forms, and returns the value of the last of body-forms. Any remaining clauses are ignored.If the value of condition is
nil, the clause fails, so thecondmoves on to the following clause, trying its condition.A clause may also look like this:
(condition)Then, if condition is non-
nilwhen tested, thecondform returns the value of condition.If every condition evaluates to
nil, so that every clause fails,condreturnsnil.The following example has four clauses, which test for the cases where the value of
xis a number, string, buffer and symbol, respectively:(cond ((numberp x) x) ((stringp x) x) ((bufferp x) (setq temporary-hack x) ; multiple body-forms (buffer-name x)) ; in one clause ((symbolp x) (symbol-value x)))Often we want to execute the last clause whenever none of the previous clauses was successful. To do this, we use
tas the condition of the last clause, like this:(tbody-forms). The formtevaluates tot, which is nevernil, so this clause never fails, provided thecondgets to it at all. For example:(setq a 5) (cond ((eq a 'hack) 'foo) (t "default")) => "default"This
condexpression returnsfooif the value ofaishack, and returns the string"default"otherwise.
Any conditional construct can be expressed with cond or with
if. Therefore, the choice between them is a matter of style.
For example:
(if a b c)
==
(cond (a b) (t c))
The cond form lets you choose between alternatives using
predicate conditions that compare values of expressions against
specific values known and written in advance. However, sometimes it
is useful to select alternatives based on more general conditions that
distinguish between broad classes of values. The pcase macro
allows you to choose between alternatives based on matching the value
of an expression against a series of patterns. A pattern can be a
literal value (for comparisons to literal values you'd use
cond), or it can be a more general description of the expected
structure of the expression's value.
Evaluate expression and choose among an arbitrary number of alternatives based on the value of expression. The possible alternatives are specified by clauses, each of which must be a list of the form
(pattern body-forms...).pcasetries to match the value of expression to the pattern of each clause, in textual order. If the value matches, the clause succeeds;pcasethen evaluates its body-forms, and returns the value of the last of body-forms. Any remaining clauses are ignored.The pattern part of a clause can be of one of two types: QPattern, a pattern quoted with a backquote; or a UPattern, which is not quoted. UPatterns are simpler, so we describe them first.
Note: In the description of the patterns below, we use “the value being matched” to refer to the value of the expression that is the first argument of
pcase.A UPattern can have the following forms:
'val- Matches if the value being matched is
equalto val.
- atom
- Matches any atom, which can be a keyword, a number, or a string. (These are self-quoting, so this kind of UPattern is actually a shorthand for
'atom.) Note that a string or a float matches any string or float with the same contents/value.
_- Matches any value. This is known as don't care or wildcard.
- symbol
- Matches any value, and additionally let-binds symbol to the value it matched, so that you can later refer to it, either in the body-forms or also later in the pattern.
(predpredfun)- Matches if the predicate function predfun returns non-
nilwhen called with the value being matched as its argument. predfun can be one of the possible forms described below.
(guardboolean-expression)- Matches if boolean-expression evaluates to non-
nil. This allows you to include in a UPattern boolean conditions that refer to symbols bound to values (including the value being matched) by previous UPatterns. Typically used inside anandUPattern, see below. For example,(and x (guard (< x 10)))is a pattern which matches any number smaller than 10 and let-binds the variablexto that number.
(letupattern expression)- Matches if the specified expression matches the specified upattern. This allows matching a pattern against the value of an arbitrary expression, not just the expression that is the first argument to
pcase. (It is calledletbecause upattern can bind symbols to values using the symbol UPattern. For example:((or `(key . ,val) (let val 5)) val).)
(appfunction upattern)- Matches if function applied to the value being matched returns a value that matches upattern. This is like the
predUPattern, except that it tests the result against UPattern, rather than against a boolean truth value. The function call can use one of the forms described below.
(orupattern1 upattern2...)- Matches if one the argument UPatterns matches. As soon as the first matching UPattern is found, the rest are not tested. For this reason, if any of the UPatterns let-bind symbols to the matched value, they should all bind the same symbols.
(andupattern1 upattern2...)- Matches if all the argument UPatterns match.
The function calls used in the
predandappUPatterns can have one of the following forms:
- function symbol, like
integerp- In this case, the named function is applied to the value being matched.
- lambda-function
(lambda (arg)body)- In this case, the lambda-function is called with one argument, the value being matched.
(func args...)- This is a function call with n specified arguments; the function is called with these n arguments and an additional n+1-th argument that is the value being matched.
Here's an illustrative example of using UPatterns:
(pcase (get-return-code x) ('success (message "Done!")) ('would-block (message "Sorry, can't do it now")) ('read-only (message "The shmliblick is read-only")) ('access-denied (message "You do not have the needed rights")) (code (message "Unknown return code %S" code)))In addition, you can use backquoted patterns that are more powerful. They allow matching the value of the expression that is the first argument of
pcaseagainst specifications of its structure. For example, you can specify that the value must be a list of 2 elements whose first element is a specific string and the second element is any value with a backquoted pattern like`("first" ,second-elem).Backquoted patterns have the form
`qpattern where qpattern can have the following forms:
(qpattern1.qpattern2)- Matches if the value being matched is a cons cell whose
carmatches qpattern1 and whosecdrmatches qpattern2. This readily generalizes to backquoted lists as in(qpattern1qpattern2...).
[qpattern1 qpattern2...qpatternm]- Matches if the value being matched is a vector of length m whose
0..(m-1)th elements match qpattern1, qpattern2 ... qpatternm, respectively.
- atom
- Matches if corresponding element of the value being matched is
equalto the specified atom.
,upattern- Matches if the corresponding element of the value being matched matches the specified upattern.
Note that uses of QPatterns can be expressed using only UPatterns, as QPatterns are implemented on top of UPatterns using
pcase-defmacro, described below. However, using QPatterns will in many cases lead to a more readable code.
Here is an example of using pcase to implement a simple
interpreter for a little expression language (note that this example
requires lexical binding, see Lexical Binding):
(defun evaluate (exp env)
(pcase exp
(`(add ,x ,y) (+ (evaluate x env) (evaluate y env)))
(`(call ,fun ,arg) (funcall (evaluate fun env) (evaluate arg env)))
(`(fn ,arg ,body) (lambda (val)
(evaluate body (cons (cons arg val) env))))
((pred numberp) exp)
((pred symbolp) (cdr (assq exp env)))
(_ (error "Unknown expression %S" exp))))
Here `(add ,x ,y) is a pattern that checks that exp is a
three-element list starting with the literal symbol add, then
extracts the second and third elements and binds them to the variables
x and y. Then it evaluates x and y and
adds the results. The call and fn patterns similarly
implement two flavors of function calls. (pred numberp) is a
pattern that simply checks that exp is a number and if so,
evaluates it. (pred symbolp) matches symbols, and returns
their association. Finally, _ is the catch-all pattern that
matches anything, so it's suitable for reporting syntax errors.
Here are some sample programs in this small language, including their evaluation results:
(evaluate '(add 1 2) nil) ;=> 3
(evaluate '(add x y) '((x . 1) (y . 2))) ;=> 3
(evaluate '(call (fn x (add 1 x)) 2) nil) ;=> 3
(evaluate '(sub 1 2) nil) ;=> error
Additional UPatterns can be defined using the pcase-defmacro
macro.
Define a new kind of UPattern for
pcase. The new UPattern will be invoked as(name actual-args). The body should describe how to rewrite the UPattern name into some other UPattern. The rewriting will be the result of evaluating body in an environment where args are bound to actual-args.
This section describes three constructs that are often used together
with if and cond to express complicated conditions. The
constructs and and or can also be used individually as
kinds of multiple conditional constructs.
This function tests for the falsehood of condition. It returns
tif condition isnil, andnilotherwise. The functionnotis identical tonull, and we recommend using the namenullif you are testing for an empty list.
The
andspecial form tests whether all the conditions are true. It works by evaluating the conditions one by one in the order written.If any of the conditions evaluates to
nil, then the result of theandmust benilregardless of the remaining conditions; soandreturnsnilright away, ignoring the remaining conditions.If all the conditions turn out non-
nil, then the value of the last of them becomes the value of theandform. Just(and), with no conditions, returnst, appropriate because all the conditions turned out non-nil. (Think about it; which one did not?)Here is an example. The first condition returns the integer 1, which is not
nil. Similarly, the second condition returns the integer 2, which is notnil. The third condition isnil, so the remaining condition is never evaluated.(and (print 1) (print 2) nil (print 3)) -| 1 -| 2 => nilHere is a more realistic example of using
and:(if (and (consp foo) (eq (car foo) 'x)) (message "foo is a list starting with x"))Note that
(car foo)is not executed if(consp foo)returnsnil, thus avoiding an error.
andexpressions can also be written using eitheriforcond. Here's how:(and arg1 arg2 arg3) == (if arg1 (if arg2 arg3)) == (cond (arg1 (cond (arg2 arg3))))
The
orspecial form tests whether at least one of the conditions is true. It works by evaluating all the conditions one by one in the order written.If any of the conditions evaluates to a non-
nilvalue, then the result of theormust be non-nil; soorreturns right away, ignoring the remaining conditions. The value it returns is the non-nilvalue of the condition just evaluated.If all the conditions turn out
nil, then theorexpression returnsnil. Just(or), with no conditions, returnsnil, appropriate because all the conditions turned outnil. (Think about it; which one did not?)For example, this expression tests whether
xis eithernilor the integer zero:(or (eq x nil) (eq x 0))Like the
andconstruct,orcan be written in terms ofcond. For example:(or arg1 arg2 arg3) == (cond (arg1) (arg2) (arg3))You could almost write
orin terms ofif, but not quite:(if arg1 arg1 (if arg2 arg2 arg3))This is not completely equivalent because it can evaluate arg1 or arg2 twice. By contrast,
(orarg1 arg2 arg3)never evaluates any argument more than once.
Iteration means executing part of a program repetitively. For
example, you might want to repeat some computation once for each element
of a list, or once for each integer from 0 to n. You can do this
in Emacs Lisp with the special form while:
whilefirst evaluates condition. If the result is non-nil, it evaluates forms in textual order. Then it reevaluates condition, and if the result is non-nil, it evaluates forms again. This process repeats until condition evaluates tonil.There is no limit on the number of iterations that may occur. The loop will continue until either condition evaluates to
nilor until an error orthrowjumps out of it (see Nonlocal Exits).The value of a
whileform is alwaysnil.(setq num 0) => 0 (while (< num 4) (princ (format "Iteration %d." num)) (setq num (1+ num))) -| Iteration 0. -| Iteration 1. -| Iteration 2. -| Iteration 3. => nilTo write a repeat-until loop, which will execute something on each iteration and then do the end-test, put the body followed by the end-test in a
prognas the first argument ofwhile, as shown here:(while (progn (forward-line 1) (not (looking-at "^$"))))This moves forward one line and continues moving by lines until it reaches an empty line. It is peculiar in that the
whilehas no body, just the end test (which also does the real work of moving point).
The dolist and dotimes macros provide convenient ways to
write two common kinds of loops.
This construct executes body once for each element of list, binding the variable var locally to hold the current element. Then it returns the value of evaluating result, or
nilif result is omitted. For example, here is how you could usedolistto define thereversefunction:(defun reverse (list) (let (value) (dolist (elt list value) (setq value (cons elt value)))))
This construct executes body once for each integer from 0 (inclusive) to count (exclusive), binding the variable var to the integer for the current iteration. Then it returns the value of evaluating result, or
nilif result is omitted. Here is an example of usingdotimesto do something 100 times:(dotimes (i 100) (insert "I will not obey absurd orders\n"))
A generator is a function that produces a potentially-infinite stream of values. Each time the function produces a value, it suspends itself and waits for a caller to request the next value.
iter-defundefines a generator function. A generator function has the same signature as a normal function, but works differently. Instead of executing body when called, a generator function returns an iterator object. That iterator runs body to generate values, emitting a value and pausing whereiter-yieldoriter-yield-fromappears. When body returns normally,iter-nextsignalsiter-end-of-sequencewith body's result as its condition data.Any kind of Lisp code is valid inside body, but
iter-yieldanditer-yield-fromcannot appear insideunwind-protectforms.
iter-lambdaproduces an unnamed generator function that works just like a generator function produced withiter-defun.
When it appears inside a generator function,
iter-yieldindicates that the current iterator should pause and return value fromiter-next.iter-yieldevaluates to thevalueparameter of next call toiter-next.
iter-yield-fromyields all the values that iterator produces and evaluates to the value that iterator's generator function returns normally. While it has control, iterator receives values sent to the iterator usingiter-next.
To use a generator function, first call it normally, producing a
iterator object. An iterator is a specific instance of a
generator. Then use iter-next to retrieve values from this
iterator. When there are no more values to pull from an iterator,
iter-next raises an iter-end-of-sequence condition with
the iterator's final value.
It's important to note that generator function bodies only execute
inside calls to iter-next. A call to a function defined with
iter-defun produces an iterator; you must drive this
iterator with iter-next for anything interesting to happen.
Each call to a generator function produces a different
iterator, each with its own state.
Retrieve the next value from iterator. If there are no more values to be generated (because iterator's generator function returned),
iter-nextsignals theiter-end-of-sequencecondition; the data value associated with this condition is the value with which iterator's generator function returned.value is sent into the iterator and becomes the value to which
iter-yieldevaluates. value is ignored for the firstiter-nextcall to a given iterator, since at the start of iterator's generator function, the generator function is not evaluating anyiter-yieldform.
If iterator is suspended inside an
unwind-protect'sbodyformand becomes unreachable, Emacs will eventually run unwind handlers after a garbage collection pass. (Note thatiter-yieldis illegal inside anunwind-protect'sunwindforms.) To ensure that these handlers are run before then, useiter-close.
Some convenience functions are provided to make working with iterators easier:
Run body with var bound to each value that iterator produces.
The Common Lisp loop facility also contains features for working with iterators. See See Loop Facility.
The following piece of code demonstrates some important principles of working with iterators.
(iter-defun my-iter (x)
(iter-yield (1+ (iter-yield (1+ x))))
;; Return normally
-1)
(let* ((iter (my-iter 5))
(iter2 (my-iter 0)))
;; Prints 6
(print (iter-next iter))
;; Prints 9
(print (iter-next iter 8))
;; Prints 1; iter and iter2 have distinct states
(print (iter-next iter2 nil))
;; We expect the iter sequence to end now
(condition-case x
(iter-next iter)
(iter-end-of-sequence
;; Prints -1, which my-iter returned normally
(print (cdr x)))))
A nonlocal exit is a transfer of control from one point in a program to another remote point. Nonlocal exits can occur in Emacs Lisp as a result of errors; you can also use them under explicit control. Nonlocal exits unbind all variable bindings made by the constructs being exited.
catch and throw
Most control constructs affect only the flow of control within the
construct itself. The function throw is the exception to this
rule of normal program execution: it performs a nonlocal exit on
request. (There are other exceptions, but they are for error handling
only.) throw is used inside a catch, and jumps back to
that catch. For example:
(defun foo-outer ()
(catch 'foo
(foo-inner)))
(defun foo-inner ()
...
(if x
(throw 'foo t))
...)
The throw form, if executed, transfers control straight back to
the corresponding catch, which returns immediately. The code
following the throw is not executed. The second argument of
throw is used as the return value of the catch.
The function throw finds the matching catch based on the
first argument: it searches for a catch whose first argument is
eq to the one specified in the throw. If there is more
than one applicable catch, the innermost one takes precedence.
Thus, in the above example, the throw specifies foo, and
the catch in foo-outer specifies the same symbol, so that
catch is the applicable one (assuming there is no other matching
catch in between).
Executing throw exits all Lisp constructs up to the matching
catch, including function calls. When binding constructs such
as let or function calls are exited in this way, the bindings
are unbound, just as they are when these constructs exit normally
(see Local Variables). Likewise, throw restores the buffer
and position saved by save-excursion (see Excursions), and
the narrowing status saved by save-restriction. It also runs
any cleanups established with the unwind-protect special form
when it exits that form (see Cleanups).
The throw need not appear lexically within the catch
that it jumps to. It can equally well be called from another function
called within the catch. As long as the throw takes place
chronologically after entry to the catch, and chronologically
before exit from it, it has access to that catch. This is why
throw can be used in commands such as exit-recursive-edit
that throw back to the editor command loop (see Recursive Editing).
Common Lisp note: Most other versions of Lisp, including Common Lisp, have several ways of transferring control nonsequentially:return,return-from, andgo, for example. Emacs Lisp has onlythrow. The cl-lib library provides versions of some of these. See Blocks and Exits.
catchestablishes a return point for thethrowfunction. The return point is distinguished from other such return points by tag, which may be any Lisp object exceptnil. The argument tag is evaluated normally before the return point is established.With the return point in effect,
catchevaluates the forms of the body in textual order. If the forms execute normally (without error or nonlocal exit) the value of the last body form is returned from thecatch.If a
throwis executed during the execution of body, specifying the same value tag, thecatchform exits immediately; the value it returns is whatever was specified as the second argument ofthrow.
The purpose of
throwis to return from a return point previously established withcatch. The argument tag is used to choose among the various existing return points; it must beeqto the value specified in thecatch. If multiple return points match tag, the innermost one is used.The argument value is used as the value to return from that
catch.If no return point is in effect with tag tag, then a
no-catcherror is signaled with data(tag value).
catch and throw
One way to use catch and throw is to exit from a doubly
nested loop. (In most languages, this would be done with a goto.)
Here we compute (foo i j) for i and j
varying from 0 to 9:
(defun search-foo ()
(catch 'loop
(let ((i 0))
(while (< i 10)
(let ((j 0))
(while (< j 10)
(if (foo i j)
(throw 'loop (list i j)))
(setq j (1+ j))))
(setq i (1+ i))))))
If foo ever returns non-nil, we stop immediately and return a
list of i and j. If foo always returns nil, the
catch returns normally, and the value is nil, since that
is the result of the while.
Here are two tricky examples, slightly different, showing two
return points at once. First, two return points with the same tag,
hack:
(defun catch2 (tag)
(catch tag
(throw 'hack 'yes)))
=> catch2
(catch 'hack
(print (catch2 'hack))
'no)
-| yes
=> no
Since both return points have tags that match the throw, it goes to
the inner one, the one established in catch2. Therefore,
catch2 returns normally with value yes, and this value is
printed. Finally the second body form in the outer catch, which is
'no, is evaluated and returned from the outer catch.
Now let's change the argument given to catch2:
(catch 'hack
(print (catch2 'quux))
'no)
=> yes
We still have two return points, but this time only the outer one has
the tag hack; the inner one has the tag quux instead.
Therefore, throw makes the outer catch return the value
yes. The function print is never called, and the
body-form 'no is never evaluated.
When Emacs Lisp attempts to evaluate a form that, for some reason, cannot be evaluated, it signals an error.
When an error is signaled, Emacs's default reaction is to print an error message and terminate execution of the current command. This is the right thing to do in most cases, such as if you type C-f at the end of the buffer.
In complicated programs, simple termination may not be what you want.
For example, the program may have made temporary changes in data
structures, or created temporary buffers that should be deleted before
the program is finished. In such cases, you would use
unwind-protect to establish cleanup expressions to be
evaluated in case of error. (See Cleanups.) Occasionally, you may
wish the program to continue execution despite an error in a subroutine.
In these cases, you would use condition-case to establish
error handlers to recover control in case of error.
Resist the temptation to use error handling to transfer control from
one part of the program to another; use catch and throw
instead. See Catch and Throw.
Signaling an error means beginning error processing. Error processing normally aborts all or part of the running program and returns to a point that is set up to handle the error (see Processing of Errors). Here we describe how to signal an error.
Most errors are signaled automatically within Lisp primitives
which you call for other purposes, such as if you try to take the
car of an integer or move forward a character at the end of the
buffer. You can also signal errors explicitly with the functions
error and signal.
Quitting, which happens when the user types C-g, is not considered an error, but it is handled almost like an error. See Quitting.
Every error specifies an error message, one way or another. The message should state what is wrong (“File does not exist”), not how things ought to be (“File must exist”). The convention in Emacs Lisp is that error messages should start with a capital letter, but should not end with any sort of punctuation.
This function signals an error with an error message constructed by applying
format-message(see Formatting Strings) to format-string and args.These examples show typical uses of
error:(error "That is an error -- try something else") error--> That is an error -- try something else (error "Invalid name `%s'" "A%%B") error--> Invalid name ‘A%%B’
errorworks by callingsignalwith two arguments: the error symbolerror, and a list containing the string returned byformat-message.The
text-quoting-stylevariable controls what quotes are generated; See Keys in Documentation. A call using a format like "Missing `%s'" with grave accents and apostrophes typically generates a message like "Missing ‘foo’" with matching curved quotes. In contrast, a call using a format like "Missing '%s'" with only apostrophes typically generates a message like "Missing ’foo’" with only closing curved quotes, an unusual style in English.Warning: If you want to use your own string as an error message verbatim, don't just write
(errorstring). If string string contains `%', ``', or `'' it may be reformatted, with undesirable results. Instead, use(error "%s"string).
This function signals an error named by error-symbol. The argument data is a list of additional Lisp objects relevant to the circumstances of the error.
The argument error-symbol must be an error symbol—a symbol defined with
define-error. This is how Emacs Lisp classifies different sorts of errors. See Error Symbols, for a description of error symbols, error conditions and condition names.If the error is not handled, the two arguments are used in printing the error message. Normally, this error message is provided by the
error-messageproperty of error-symbol. If data is non-nil, this is followed by a colon and a comma separated list of the unevaluated elements of data. Forerror, the error message is the car of data (that must be a string). Subcategories offile-errorare handled specially.The number and significance of the objects in data depends on error-symbol. For example, with a
wrong-type-argumenterror, there should be two objects in the list: a predicate that describes the type that was expected, and the object that failed to fit that type.Both error-symbol and data are available to any error handlers that handle the error:
condition-casebinds a local variable to a list of the form(error-symbol.data)(see Handling Errors).The function
signalnever returns.(signal 'wrong-number-of-arguments '(x y)) error--> Wrong number of arguments: x, y (signal 'no-such-error '("My unknown error condition")) error--> peculiar error: "My unknown error condition"
This function behaves exactly like
error, except that it uses the error symboluser-errorrather thanerror. As the name suggests, this is intended to report errors on the part of the user, rather than errors in the code itself. For example, if you try to use the commandInfo-history-back(l) to move back beyond the start of your Info browsing history, Emacs signals auser-error. Such errors do not cause entry to the debugger, even whendebug-on-erroris non-nil. See Error Debugging.
Common Lisp note: Emacs Lisp has nothing like the Common Lisp concept of continuable errors.
When an error is signaled, signal searches for an active
handler for the error. A handler is a sequence of Lisp
expressions designated to be executed if an error happens in part of the
Lisp program. If the error has an applicable handler, the handler is
executed, and control resumes following the handler. The handler
executes in the environment of the condition-case that
established it; all functions called within that condition-case
have already been exited, and the handler cannot return to them.
If there is no applicable handler for the error, it terminates the
current command and returns control to the editor command loop. (The
command loop has an implicit handler for all kinds of errors.) The
command loop's handler uses the error symbol and associated data to
print an error message. You can use the variable
command-error-function to control how this is done:
This variable, if non-
nil, specifies a function to use to handle errors that return control to the Emacs command loop. The function should take three arguments: data, a list of the same form thatcondition-casewould bind to its variable; context, a string describing the situation in which the error occurred, or (more often)nil; and caller, the Lisp function which called the primitive that signaled the error.
An error that has no explicit handler may call the Lisp debugger. The
debugger is enabled if the variable debug-on-error (see Error Debugging) is non-nil. Unlike error handlers, the debugger runs
in the environment of the error, so that you can examine values of
variables precisely as they were at the time of the error.
The usual effect of signaling an error is to terminate the command
that is running and return immediately to the Emacs editor command loop.
You can arrange to trap errors occurring in a part of your program by
establishing an error handler, with the special form
condition-case. A simple example looks like this:
(condition-case nil
(delete-file filename)
(error nil))
This deletes the file named filename, catching any error and
returning nil if an error occurs. (You can use the macro
ignore-errors for a simple case like this; see below.)
The condition-case construct is often used to trap errors that
are predictable, such as failure to open a file in a call to
insert-file-contents. It is also used to trap errors that are
totally unpredictable, such as when the program evaluates an expression
read from the user.
The second argument of condition-case is called the
protected form. (In the example above, the protected form is a
call to delete-file.) The error handlers go into effect when
this form begins execution and are deactivated when this form returns.
They remain in effect for all the intervening time. In particular, they
are in effect during the execution of functions called by this form, in
their subroutines, and so on. This is a good thing, since, strictly
speaking, errors can be signaled only by Lisp primitives (including
signal and error) called by the protected form, not by the
protected form itself.
The arguments after the protected form are handlers. Each handler
lists one or more condition names (which are symbols) to specify
which errors it will handle. The error symbol specified when an error
is signaled also defines a list of condition names. A handler applies
to an error if they have any condition names in common. In the example
above, there is one handler, and it specifies one condition name,
error, which covers all errors.
The search for an applicable handler checks all the established handlers
starting with the most recently established one. Thus, if two nested
condition-case forms offer to handle the same error, the inner of
the two gets to handle it.
If an error is handled by some condition-case form, this
ordinarily prevents the debugger from being run, even if
debug-on-error says this error should invoke the debugger.
If you want to be able to debug errors that are caught by a
condition-case, set the variable debug-on-signal to a
non-nil value. You can also specify that a particular handler
should let the debugger run first, by writing debug among the
conditions, like this:
(condition-case nil
(delete-file filename)
((debug error) nil))
The effect of debug here is only to prevent
condition-case from suppressing the call to the debugger. Any
given error will invoke the debugger only if debug-on-error and
the other usual filtering mechanisms say it should. See Error Debugging.
The macro
condition-case-unless-debugprovides another way to handle debugging of such forms. It behaves exactly likecondition-case, unless the variabledebug-on-erroris non-nil, in which case it does not handle any errors at all.
Once Emacs decides that a certain handler handles the error, it
returns control to that handler. To do so, Emacs unbinds all variable
bindings made by binding constructs that are being exited, and
executes the cleanups of all unwind-protect forms that are
being exited. Once control arrives at the handler, the body of the
handler executes normally.
After execution of the handler body, execution returns from the
condition-case form. Because the protected form is exited
completely before execution of the handler, the handler cannot resume
execution at the point of the error, nor can it examine variable
bindings that were made within the protected form. All it can do is
clean up and proceed.
Error signaling and handling have some resemblance to throw and
catch (see Catch and Throw), but they are entirely separate
facilities. An error cannot be caught by a catch, and a
throw cannot be handled by an error handler (though using
throw when there is no suitable catch signals an error
that can be handled).
This special form establishes the error handlers handlers around the execution of protected-form. If protected-form executes without error, the value it returns becomes the value of the
condition-caseform; in this case, thecondition-casehas no effect. Thecondition-caseform makes a difference when an error occurs during protected-form.Each of the handlers is a list of the form
(conditions body...). Here conditions is an error condition name to be handled, or a list of condition names (which can includedebugto allow the debugger to run before the handler); body is one or more Lisp expressions to be executed when this handler handles an error. Here are examples of handlers:(error nil) (arith-error (message "Division by zero")) ((arith-error file-error) (message "Either division by zero or failure to open a file"))Each error that occurs has an error symbol that describes what kind of error it is, and which describes also a list of condition names (see Error Symbols). Emacs searches all the active
condition-caseforms for a handler that specifies one or more of these condition names; the innermost matchingcondition-casehandles the error. Within thiscondition-case, the first applicable handler handles the error.After executing the body of the handler, the
condition-casereturns normally, using the value of the last form in the handler body as the overall value.The argument var is a variable.
condition-casedoes not bind this variable when executing the protected-form, only when it handles an error. At that time, it binds var locally to an error description, which is a list giving the particulars of the error. The error description has the form(error-symbol.data). The handler can refer to this list to decide what to do. For example, if the error is for failure opening a file, the file name is the second element of data—the third element of the error description.If var is
nil, that means no variable is bound. Then the error symbol and associated data are not available to the handler.Sometimes it is necessary to re-throw a signal caught by
condition-case, for some outer-level handler to catch. Here's how to do that:(signal (car err) (cdr err))where
erris the error description variable, the first argument tocondition-casewhose error condition you want to re-throw. See Definition of signal.
This function returns the error message string for a given error descriptor. It is useful if you want to handle an error by printing the usual error message for that error. See Definition of signal.
Here is an example of using condition-case to handle the error
that results from dividing by zero. The handler displays the error
message (but without a beep), then returns a very large number.
(defun safe-divide (dividend divisor)
(condition-case err
;; Protected form.
(/ dividend divisor)
;; The handler.
(arith-error ; Condition.
;; Display the usual message for this error.
(message "%s" (error-message-string err))
1000000)))
=> safe-divide
(safe-divide 5 0)
-| Arithmetic error: (arith-error)
=> 1000000
The handler specifies condition name arith-error so that it
will handle only division-by-zero errors. Other kinds of errors will
not be handled (by this condition-case). Thus:
(safe-divide nil 3)
error--> Wrong type argument: number-or-marker-p, nil
Here is a condition-case that catches all kinds of errors,
including those from error:
(setq baz 34)
=> 34
(condition-case err
(if (eq baz 35)
t
;; This is a call to the function error.
(error "Rats! The variable %s was %s, not 35" 'baz baz))
;; This is the handler; it is not a form.
(error (princ (format "The error was: %s" err))
2))
-| The error was: (error "Rats! The variable baz was 34, not 35")
=> 2
This construct executes body, ignoring any errors that occur during its execution. If the execution is without error,
ignore-errorsreturns the value of the last form in body; otherwise, it returnsnil.Here's the example at the beginning of this subsection rewritten using
ignore-errors:(ignore-errors (delete-file filename))
This macro is like a milder version of
ignore-errors. Rather than suppressing errors altogether, it converts them into messages. It uses the string format to format the message. format should contain a single `%'-sequence; e.g.,"Error: %S". Usewith-demoted-errorsaround code that is not expected to signal errors, but should be robust if one does occur. Note that this macro usescondition-case-unless-debugrather thancondition-case.
When you signal an error, you specify an error symbol to specify the kind of error you have in mind. Each error has one and only one error symbol to categorize it. This is the finest classification of errors defined by the Emacs Lisp language.
These narrow classifications are grouped into a hierarchy of wider
classes called error conditions, identified by condition
names. The narrowest such classes belong to the error symbols
themselves: each error symbol is also a condition name. There are also
condition names for more extensive classes, up to the condition name
error which takes in all kinds of errors (but not quit).
Thus, each error has one or more condition names: error, the
error symbol if that is distinct from error, and perhaps some
intermediate classifications.
In order for a symbol to be an error symbol, it must be defined with
define-errorwhich takes a parent condition (defaults toerror). This parent defines the conditions that this kind of error belongs to. The transitive set of parents always includes the error symbol itself, and the symbolerror. Because quitting is not considered an error, the set of parents ofquitis just(quit).
In addition to its parents, the error symbol has a message which is a string to be printed when that error is signaled but not handled. If that message is not valid, the error message `peculiar error' is used. See Definition of signal.
Internally, the set of parents is stored in the error-conditions
property of the error symbol and the message is stored in the
error-message property of the error symbol.
Here is how we define a new error symbol, new-error:
(define-error 'new-error "A new error" 'my-own-errors)
This error has several condition names: new-error, the narrowest
classification; my-own-errors, which we imagine is a wider
classification; and all the conditions of my-own-errors which should
include error, which is the widest of all.
The error string should start with a capital letter but it should not end with a period. This is for consistency with the rest of Emacs.
Naturally, Emacs will never signal new-error on its own; only
an explicit call to signal (see Definition of signal) in
your code can do this:
(signal 'new-error '(x y))
error--> A new error: x, y
This error can be handled through any of its condition names.
This example handles new-error and any other errors in the class
my-own-errors:
(condition-case foo
(bar nil t)
(my-own-errors nil))
The significant way that errors are classified is by their condition
names—the names used to match errors with handlers. An error symbol
serves only as a convenient way to specify the intended error message
and list of condition names. It would be cumbersome to give
signal a list of condition names rather than one error symbol.
By contrast, using only error symbols without condition names would
seriously decrease the power of condition-case. Condition names
make it possible to categorize errors at various levels of generality
when you write an error handler. Using error symbols alone would
eliminate all but the narrowest level of classification.
See Standard Errors, for a list of the main error symbols and their conditions.
The unwind-protect construct is essential whenever you
temporarily put a data structure in an inconsistent state; it permits
you to make the data consistent again in the event of an error or
throw. (Another more specific cleanup construct that is used only for
changes in buffer contents is the atomic change group; Atomic Changes.)
unwind-protectexecutes body-form with a guarantee that the cleanup-forms will be evaluated if control leaves body-form, no matter how that happens. body-form may complete normally, or execute athrowout of theunwind-protect, or cause an error; in all cases, the cleanup-forms will be evaluated.If body-form finishes normally,
unwind-protectreturns the value of body-form, after it evaluates the cleanup-forms. If body-form does not finish,unwind-protectdoes not return any value in the normal sense.Only body-form is protected by the
unwind-protect. If any of the cleanup-forms themselves exits nonlocally (via athrowor an error),unwind-protectis not guaranteed to evaluate the rest of them. If the failure of one of the cleanup-forms has the potential to cause trouble, then protect it with anotherunwind-protectaround that form.The number of currently active
unwind-protectforms counts, together with the number of local variable bindings, against the limitmax-specpdl-size(see Local Variables).
For example, here we make an invisible buffer for temporary use, and make sure to kill it before finishing:
(let ((buffer (get-buffer-create " *temp*")))
(with-current-buffer buffer
(unwind-protect
body-form
(kill-buffer buffer))))
You might think that we could just as well write (kill-buffer
(current-buffer)) and dispense with the variable buffer.
However, the way shown above is safer, if body-form happens to
get an error after switching to a different buffer! (Alternatively,
you could write a save-current-buffer around body-form,
to ensure that the temporary buffer becomes current again in time to
kill it.)
Emacs includes a standard macro called with-temp-buffer which
expands into more or less the code shown above (see Current Buffer). Several of the macros defined in
this manual use unwind-protect in this way.
Here is an actual example derived from an FTP package. It creates a
process (see Processes) to try to establish a connection to a remote
machine. As the function ftp-login is highly susceptible to
numerous problems that the writer of the function cannot anticipate, it
is protected with a form that guarantees deletion of the process in the
event of failure. Otherwise, Emacs might fill up with useless
subprocesses.
(let ((win nil))
(unwind-protect
(progn
(setq process (ftp-setup-buffer host file))
(if (setq win (ftp-login process host user password))
(message "Logged in")
(error "Ftp login failed")))
(or win (and process (delete-process process)))))
This example has a small bug: if the user types C-g to
quit, and the quit happens immediately after the function
ftp-setup-buffer returns but before the variable process is
set, the process will not be killed. There is no easy way to fix this bug,
but at least it is very unlikely.
A variable is a name used in a program to stand for a value. In Lisp, each variable is represented by a Lisp symbol (see Symbols). The variable name is simply the symbol's name, and the variable's value is stored in the symbol's value cell6. See Symbol Components. In Emacs Lisp, the use of a symbol as a variable is independent of its use as a function name.
As previously noted in this manual, a Lisp program is represented primarily by Lisp objects, and only secondarily as text. The textual form of a Lisp program is given by the read syntax of the Lisp objects that constitute the program. Hence, the textual form of a variable in a Lisp program is written using the read syntax for the symbol representing the variable.
The simplest way to use a variable is globally. This means that the variable has just one value at a time, and this value is in effect (at least for the moment) throughout the Lisp system. The value remains in effect until you specify a new one. When a new value replaces the old one, no trace of the old value remains in the variable.
You specify a value for a symbol with setq. For example,
(setq x '(a b))
gives the variable x the value (a b). Note that
setq is a special form (see Special Forms); it does not
evaluate its first argument, the name of the variable, but it does
evaluate the second argument, the new value.
Once the variable has a value, you can refer to it by using the symbol itself as an expression. Thus,
x => (a b)
assuming the setq form shown above has already been executed.
If you do set the same variable again, the new value replaces the old one:
x
=> (a b)
(setq x 4)
=> 4
x
=> 4
In Emacs Lisp, certain symbols normally evaluate to themselves. These
include nil and t, as well as any symbol whose name starts
with `:' (these are called keywords). These symbols cannot
be rebound, nor can their values be changed. Any attempt to set or bind
nil or t signals a setting-constant error. The
same is true for a keyword (a symbol whose name starts with `:'),
if it is interned in the standard obarray, except that setting such a
symbol to itself is not an error.
nil == 'nil
=> nil
(setq nil 500)
error--> Attempt to set constant symbol: nil
function returns
tif object is a symbol whose name starts with `:', interned in the standard obarray, and returnsnilotherwise.
These constants are fundamentally different from the constants
defined using the defconst special form (see Defining Variables). A defconst form serves to inform human readers
that you do not intend to change the value of a variable, but Emacs
does not raise an error if you actually change it.
Global variables have values that last until explicitly superseded with new values. Sometimes it is useful to give a variable a local value—a value that takes effect only within a certain part of a Lisp program. When a variable has a local value, we say that it is locally bound to that value, and that it is a local variable.
For example, when a function is called, its argument variables
receive local values, which are the actual arguments supplied to the
function call; these local bindings take effect within the body of the
function. To take another example, the let special form
explicitly establishes local bindings for specific variables, which
take effect within the body of the let form.
We also speak of the global binding, which is where (conceptually) the global value is kept.
Establishing a local binding saves away the variable's previous
value (or lack of one). We say that the previous value is
shadowed. Both global and local values may be shadowed. If a
local binding is in effect, using setq on the local variable
stores the specified value in the local binding. When that local
binding is no longer in effect, the previously shadowed value (or lack
of one) comes back.
A variable can have more than one local binding at a time (e.g., if
there are nested let forms that bind the variable). The
current binding is the local binding that is actually in effect.
It determines the value returned by evaluating the variable symbol,
and it is the binding acted on by setq.
For most purposes, you can think of the current binding as the innermost local binding, or the global binding if there is no local binding. To be more precise, a rule called the scoping rule determines where in a program a local binding takes effect. The default scoping rule in Emacs Lisp is called dynamic scoping, which simply states that the current binding at any given point in the execution of a program is the most recently-created binding for that variable that still exists. For details about dynamic scoping, and an alternative scoping rule called lexical scoping, See Variable Scoping.
The special forms let and let* exist to create local
bindings:
This special form sets up local bindings for a certain set of variables, as specified by bindings, and then evaluates all of the forms in textual order. Its return value is the value of the last form in forms.
Each of the bindings is either (i) a symbol, in which case that symbol is locally bound to
nil; or (ii) a list of the form(symbol value-form), in which case symbol is locally bound to the result of evaluating value-form. If value-form is omitted,nilis used.All of the value-forms in bindings are evaluated in the order they appear and before binding any of the symbols to them. Here is an example of this:
zis bound to the old value ofy, which is 2, not the new value ofy, which is 1.(setq y 2) => 2 (let ((y 1) (z y)) (list y z)) => (1 2)
This special form is like
let, but it binds each variable right after computing its local value, before computing the local value for the next variable. Therefore, an expression in bindings can refer to the preceding symbols bound in thislet*form. Compare the following example with the example above forlet.(setq y 2) => 2 (let* ((y 1) (z y)) ; Use the just-established value ofy. (list y z)) => (1 1)
Here is a complete list of the other facilities that create local bindings:
Variables can also have buffer-local bindings (see Buffer-Local Variables); a few variables have terminal-local bindings (see Multiple Terminals). These kinds of bindings work somewhat like ordinary local bindings, but they are localized depending on where you are in Emacs.
This variable defines the limit on the total number of local variable bindings and
unwind-protectcleanups (see Cleaning Up from Nonlocal Exits) that are allowed before Emacs signals an error (with data"Variable binding depth exceeds max-specpdl-size").This limit, with the associated error when it is exceeded, is one way that Lisp avoids infinite recursion on an ill-defined function.
max-lisp-eval-depthprovides another limit on depth of nesting. See Eval.The default value is 1300. Entry to the Lisp debugger increases the value, if there is little room left, to make sure the debugger itself has room to execute.
We say that a variable is void if its symbol has an unassigned value cell (see Symbol Components).
Under Emacs Lisp's default dynamic scoping rule (see Variable Scoping), the value cell stores the variable's current (local or
global) value. Note that an unassigned value cell is not the
same as having nil in the value cell. The symbol nil is
a Lisp object and can be the value of a variable, just as any other
object can be; but it is still a value. If a variable is void, trying
to evaluate the variable signals a void-variable error, instead
of returning a value.
Under the optional lexical scoping rule, the value cell only holds the variable's global value—the value outside of any lexical binding construct. When a variable is lexically bound, the local value is determined by the lexical environment; hence, variables can have local values even if their symbols' value cells are unassigned.
This function empties out the value cell of symbol, making the variable void. It returns symbol.
If symbol has a dynamic local binding,
makunboundvoids the current binding, and this voidness lasts only as long as the local binding is in effect. Afterwards, the previously shadowed local or global binding is reexposed; then the variable will no longer be void, unless the reexposed binding is void too.Here are some examples (assuming dynamic binding is in effect):
(setq x 1) ; Put a value in the global binding. => 1 (let ((x 2)) ; Locally bind it. (makunbound 'x) ; Void the local binding. x) error--> Symbol's value as variable is void: x x ; The global binding is unchanged. => 1 (let ((x 2)) ; Locally bind it. (let ((x 3)) ; And again. (makunbound 'x) ; Void the innermost-local binding. x)) ; And refer: it's void. error--> Symbol's value as variable is void: x (let ((x 2)) (let ((x 3)) (makunbound 'x)) ; Void inner binding, then remove it. x) ; Now outerletbinding is visible. => 2
This function returns
tif variable (a symbol) is not void, andnilif it is void.Here are some examples (assuming dynamic binding is in effect):
(boundp 'abracadabra) ; Starts out void. => nil (let ((abracadabra 5)) ; Locally bind it. (boundp 'abracadabra)) => t (boundp 'abracadabra) ; Still globally void. => nil (setq abracadabra 5) ; Make it globally nonvoid. => 5 (boundp 'abracadabra) => t
A variable definition is a construct that announces your
intention to use a symbol as a global variable. It uses the special
forms defvar or defconst, which are documented below.
A variable definition serves three purposes. First, it informs people who read the code that the symbol is intended to be used a certain way (as a variable). Second, it informs the Lisp system of this, optionally supplying an initial value and a documentation string. Third, it provides information to programming tools such as etags, allowing them to find where the variable was defined.
The difference between defconst and defvar is mainly a
matter of intent, serving to inform human readers of whether the value
should ever change. Emacs Lisp does not actually prevent you from
changing the value of a variable defined with defconst. One
notable difference between the two forms is that defconst
unconditionally initializes the variable, whereas defvar
initializes it only if it is originally void.
To define a customizable variable, you should use defcustom
(which calls defvar as a subroutine). See Variable Definitions.
This special form defines symbol as a variable. Note that symbol is not evaluated; the symbol to be defined should appear explicitly in the
defvarform. The variable is marked as special, meaning that it should always be dynamically bound (see Variable Scoping).If value is specified, and symbol is void (i.e., it has no dynamically bound value; see Void Variables), then value is evaluated and symbol is set to the result. But if symbol is not void, value is not evaluated, and symbol's value is left unchanged. If value is omitted, the value of symbol is not changed in any case.
If symbol has a buffer-local binding in the current buffer,
defvaracts on the default value, which is buffer-independent, rather than the buffer-local binding. It sets the default value if the default value is void. See Buffer-Local Variables.If symbol is already lexically bound (e.g., if the
defvarform occurs in aletform with lexical binding enabled), thendefvarsets the dynamic value. The lexical binding remains in effect until its binding construct exits. See Variable Scoping.When you evaluate a top-level
defvarform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunarranges to set the variable unconditionally, without testing whether its value is void.If the doc-string argument is supplied, it specifies the documentation string for the variable (stored in the symbol's
variable-documentationproperty). See Documentation.Here are some examples. This form defines
foobut does not initialize it:(defvar foo) => fooThis example initializes the value of
barto23, and gives it a documentation string:(defvar bar 23 "The normal weight of a bar.") => barThe
defvarform returns symbol, but it is normally used at top level in a file where its value does not matter.
This special form defines symbol as a value and initializes it. It informs a person reading your code that symbol has a standard global value, established here, that should not be changed by the user or by other programs. Note that symbol is not evaluated; the symbol to be defined must appear explicitly in the
defconst.The
defconstform, likedefvar, marks the variable as special, meaning that it should always be dynamically bound (see Variable Scoping). In addition, it marks the variable as risky (see File Local Variables).
defconstalways evaluates value, and sets the value of symbol to the result. If symbol does have a buffer-local binding in the current buffer,defconstsets the default value, not the buffer-local value. (But you should not be making buffer-local bindings for a symbol that is defined withdefconst.)An example of the use of
defconstis Emacs's definition offloat-pi—the mathematical constant pi, which ought not to be changed by anyone (attempts by the Indiana State Legislature notwithstanding). As the second form illustrates, however,defconstis only advisory.(defconst float-pi 3.141592653589793 "The value of Pi.") => float-pi (setq float-pi 3) => float-pi float-pi => 3
Warning: If you use a defconst or defvar
special form while the variable has a local binding (made with
let, or a function argument), it sets the local binding rather
than the global binding. This is not what you usually want. To
prevent this, use these special forms at top level in a file, where
normally no local binding is in effect, and make sure to load the file
before making a local binding for the variable.
When you define a variable whose value is a function, or a list of functions, use a name that ends in `-function' or `-functions', respectively.
There are several other variable name conventions; here is a complete list:
nil for success and nil for failure.
nil or not.
Since such variables often end up acquiring more values over time,
this convention is not strongly recommended.
When you define a variable, always consider whether you should mark it as safe or risky; see File Local Variables.
When defining and initializing a variable that holds a complicated
value (such as a keymap with bindings in it), it's best to put the
entire computation of the value into the defvar, like this:
(defvar my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
map)
docstring)
This method has several benefits. First, if the user quits while
loading the file, the variable is either still uninitialized or
initialized properly, never in-between. If it is still uninitialized,
reloading the file will initialize it properly. Second, reloading the
file once the variable is initialized will not alter it; that is
important if the user has run hooks to alter part of the contents
(such as, to rebind keys). Third, evaluating the defvar form
with C-M-x will reinitialize the map completely.
Putting so much code in the defvar form has one disadvantage:
it puts the documentation string far away from the line which names the
variable. Here's a safe way to avoid that:
(defvar my-mode-map nil
docstring)
(unless my-mode-map
(let ((map (make-sparse-keymap)))
(define-key map "\C-c\C-a" 'my-command)
...
(setq my-mode-map map)))
This has all the same advantages as putting the initialization inside
the defvar, except that you must type C-M-x twice, once on
each form, if you do want to reinitialize the variable.
The usual way to reference a variable is to write the symbol which names it. See Symbol Forms.
Occasionally, you may want to reference a variable which is only
determined at run time. In that case, you cannot specify the variable
name in the text of the program. You can use the symbol-value
function to extract the value.
This function returns the value stored in symbol's value cell. This is where the variable's current (dynamic) value is stored. If the variable has no local binding, this is simply its global value. If the variable is void, a
void-variableerror is signaled.If the variable is lexically bound, the value reported by
symbol-valueis not necessarily the same as the variable's lexical value, which is determined by the lexical environment rather than the symbol's value cell. See Variable Scoping.(setq abracadabra 5) => 5 (setq foo 9) => 9 ;; Here the symbolabracadabra;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value 'abracadabra)) => foo ;; Here, the value ofabracadabra, ;; which isfoo, ;; is the symbol whose value is examined. (let ((abracadabra 'foo)) (symbol-value abracadabra)) => 9 (symbol-value 'abracadabra) => 5
The usual way to change the value of a variable is with the special
form setq. When you need to compute the choice of variable at
run time, use the function set.
This special form is the most common method of changing a variable's value. Each symbol is given a new value, which is the result of evaluating the corresponding form. The current binding of the symbol is changed.
setqdoes not evaluate symbol; it sets the symbol that you write. We say that this argument is automatically quoted. The `q' insetqstands for “quoted”.The value of the
setqform is the value of the last form.(setq x (1+ 2)) => 3 x ;xnow has a global value. => 3 (let ((x 5)) (setq x 6) ; The local binding ofxis set. x) => 6 x ; The global value is unchanged. => 3Note that the first form is evaluated, then the first symbol is set, then the second form is evaluated, then the second symbol is set, and so on:
(setq x 10 ; Notice thatxis set before y (1+ x)) ; the value ofyis computed. => 11
This function puts value in the value cell of symbol. Since it is a function rather than a special form, the expression written for symbol is evaluated to obtain the symbol to set. The return value is value.
When dynamic variable binding is in effect (the default),
sethas the same effect assetq, apart from the fact thatsetevaluates its symbol argument whereassetqdoes not. But when a variable is lexically bound,setaffects its dynamic value, whereassetqaffects its current (lexical) value. See Variable Scoping.(set one 1) error--> Symbol's value as variable is void: one (set 'one 1) => 1 (set 'two 'one) => one (set two 2) ;twoevaluates to symbolone. => 2 one ; So it isonethat was set. => 2 (let ((one 1)) ; This binding ofoneis set, (set 'one 3) ; not the global value. one) => 3 one => 2If symbol is not actually a symbol, a
wrong-type-argumenterror is signaled.(set '(x y) 'z) error--> Wrong type argument: symbolp, (x y)
When you create a local binding for a variable, that binding takes effect only within a limited portion of the program (see Local Variables). This section describes exactly what this means.
Each local binding has a certain scope and extent. Scope refers to where in the textual source code the binding can be accessed. Extent refers to when, as the program is executing, the binding exists.
By default, the local bindings that Emacs creates are dynamic
bindings. Such a binding has dynamic scope, meaning that any
part of the program can potentially access the variable binding. It
also has dynamic extent, meaning that the binding lasts only
while the binding construct (such as the body of a let form) is
being executed.
Emacs can optionally create lexical bindings. A lexical binding has lexical scope, meaning that any reference to the variable must be located textually within the binding construct7. It also has indefinite extent, meaning that under some circumstances the binding can live on even after the binding construct has finished executing, by means of special objects called closures.
The following subsections describe dynamic binding and lexical binding in greater detail, and how to enable lexical binding in Emacs Lisp programs.
By default, the local variable bindings made by Emacs are dynamic bindings. When a variable is dynamically bound, its current binding at any point in the execution of the Lisp program is simply the most recently-created dynamic local binding for that symbol, or the global binding if there is no such local binding.
Dynamic bindings have dynamic scope and extent, as shown by the following example:
(defvar x -99) ;xreceives an initial value of −99. (defun getx () x) ;xis used free in this function. (let ((x 1)) ;xis dynamically bound. (getx)) => 1 ;; After theletform finishes,xreverts to its ;; previous value, which is −99. (getx) => -99
The function getx refers to x. This is a free
reference, in the sense that there is no binding for x within
that defun construct itself. When we call getx from
within a let form in which x is (dynamically) bound, it
retrieves the local value (i.e., 1). But when we call getx
outside the let form, it retrieves the global value (i.e.,
−99).
Here is another example, which illustrates setting a dynamically
bound variable using setq:
(defvar x -99) ;xreceives an initial value of −99. (defun addx () (setq x (1+ x))) ; Add 1 toxand return its new value. (let ((x 1)) (addx) (addx)) => 3 ; The twoaddxcalls add toxtwice. ;; After theletform finishes,xreverts to its ;; previous value, which is −99. (addx) => -98
Dynamic binding is implemented in Emacs Lisp in a simple way. Each symbol has a value cell, which specifies its current dynamic value (or absence of value). See Symbol Components. When a symbol is given a dynamic local binding, Emacs records the contents of the value cell (or absence thereof) in a stack, and stores the new local value in the value cell. When the binding construct finishes executing, Emacs pops the old value off the stack, and puts it in the value cell.
Dynamic binding is a powerful feature, as it allows programs to refer to variables that are not defined within their local textual scope. However, if used without restraint, this can also make programs hard to understand. There are two clean ways to use this technique:
let
form where the variable was bound. If this convention is followed
consistently throughout a program, the value of the variable will not
affect, nor be affected by, any uses of the same variable symbol
elsewhere in the program.
defvar, defconst, or
defcustom. See Defining Variables. Usually, the definition
should be at top-level in an Emacs Lisp file. As far as possible, it
should include a documentation string which explains the meaning and
purpose of the variable. You should also choose the variable's name
to avoid name conflicts (see Coding Conventions).
Then you can bind the variable anywhere in a program, knowing reliably what the effect will be. Wherever you encounter the variable, it will be easy to refer back to the definition, e.g., via the C-h v command (provided the variable definition has been loaded into Emacs). See Name Help.
For example, it is common to use local bindings for customizable
variables like case-fold-search:
(defun search-for-abc ()
"Search for the string \"abc\", ignoring case differences."
(let ((case-fold-search nil))
(re-search-forward "abc")))
Lexical binding was introduced to Emacs, as an optional feature, in version 24.1. We expect its importance to increase in the future. Lexical binding opens up many more opportunities for optimization, so programs using it are likely to run faster in future Emacs versions. Lexical binding is also more compatible with concurrency, which we want to add to Emacs in the future.
A lexically-bound variable has lexical scope, meaning that any reference to the variable must be located textually within the binding construct. Here is an example (see Using Lexical Binding, for how to actually enable lexical binding):
(let ((x 1)) ;xis lexically bound. (+ x 3)) => 4 (defun getx () x) ;xis used free in this function. (let ((x 1)) ;xis lexically bound. (getx)) error--> Symbol's value as variable is void: x
Here, the variable x has no global value. When it is lexically
bound within a let form, it can be used in the textual confines
of that let form. But it can not be used from within a
getx function called from the let form, since the
function definition of getx occurs outside the let form
itself.
Here is how lexical binding works. Each binding construct defines a lexical environment, specifying the symbols that are bound within the construct and their local values. When the Lisp evaluator wants the current value of a variable, it looks first in the lexical environment; if the variable is not specified in there, it looks in the symbol's value cell, where the dynamic value is stored.
(Internally, the lexical environment is an alist of symbol-value
pairs, with the final element in the alist being the symbol t
rather than a cons cell. Such an alist can be passed as the second
argument to the eval function, in order to specify a lexical
environment in which to evaluate a form. See Eval. Most Emacs
Lisp programs, however, should not interact directly with lexical
environments in this way; only specialized programs like debuggers.)
Lexical bindings have indefinite extent. Even after a binding construct has finished executing, its lexical environment can be “kept around” in Lisp objects called closures. A closure is created when you define a named or anonymous function with lexical binding enabled. See Closures, for details.
When a closure is called as a function, any lexical variable references within its definition use the retained lexical environment. Here is an example:
(defvar my-ticker nil) ; We will use this dynamically bound ; variable to store a closure. (let ((x 0)) ;xis lexically bound. (setq my-ticker (lambda () (setq x (1+ x))))) => (closure ((x . 0) t) () (setq x (1+ x))) (funcall my-ticker) => 1 (funcall my-ticker) => 2 (funcall my-ticker) => 3 x ; Note thatxhas no global value. error--> Symbol's value as variable is void: x
The let binding defines a lexical environment in which the
variable x is locally bound to 0. Within this binding
construct, we define a lambda expression which increments x by
one and returns the incremented value. This lambda expression is
automatically turned into a closure, in which the lexical environment
lives on even after the let binding construct has exited. Each
time we evaluate the closure, it increments x, using the
binding of x in that lexical environment.
Note that functions like symbol-value, boundp, and
set only retrieve or modify a variable's dynamic binding
(i.e., the contents of its symbol's value cell). Also, the code in
the body of a defun or defmacro cannot refer to
surrounding lexical variables.
When loading an Emacs Lisp file or evaluating a Lisp buffer, lexical
binding is enabled if the buffer-local variable lexical-binding
is non-nil:
If this buffer-local variable is non-
nil, Emacs Lisp files and buffers are evaluated using lexical binding instead of dynamic binding. (However, special variables are still dynamically bound; see below.) Ifnil, dynamic binding is used for all local variables. This variable is typically set for a whole Emacs Lisp file, as a file local variable (see File Local Variables). Note that unlike other such variables, this one must be set in the first line of a file.
When evaluating Emacs Lisp code directly using an eval call,
lexical binding is enabled if the lexical argument to
eval is non-nil. See Eval.
Even when lexical binding is enabled, certain variables will
continue to be dynamically bound. These are called special
variables. Every variable that has been defined with defvar,
defcustom or defconst is a special variable
(see Defining Variables). All other variables are subject to
lexical binding.
This function returns non-
nilif symbol is a special variable (i.e., it has adefvar,defcustom, ordefconstvariable definition). Otherwise, the return value isnil.
The use of a special variable as a formal argument in a function is discouraged. Doing so gives rise to unspecified behavior when lexical binding mode is enabled (it may use lexical binding sometimes, and dynamic binding other times).
Converting an Emacs Lisp program to lexical binding is easy. First,
add a file-local variable setting of lexical-binding to
t in the header line of the Emacs Lisp source file (see File Local Variables). Second, check that every variable in the program
which needs to be dynamically bound has a variable definition, so that
it is not inadvertently bound lexically.
A simple way to find out which variables need a variable definition
is to byte-compile the source file. See Byte Compilation. If a
non-special variable is used outside of a let form, the
byte-compiler will warn about reference or assignment to a free
variable. If a non-special variable is bound but not used within a
let form, the byte-compiler will warn about an unused lexical
variable. The byte-compiler will also issue a warning if you use a
special variable as a function argument.
(To silence byte-compiler warnings about unused variables, just use a variable name that start with an underscore. The byte-compiler interprets this as an indication that this is a variable known not to be used.)
Global and local variable bindings are found in most programming languages in one form or another. Emacs, however, also supports additional, unusual kinds of variable binding, such as buffer-local bindings, which apply only in one buffer. Having different values for a variable in different buffers is an important customization method. (Variables can also have bindings that are local to each terminal. See Multiple Terminals.)
A buffer-local variable has a buffer-local binding associated with a particular buffer. The binding is in effect when that buffer is current; otherwise, it is not in effect. If you set the variable while a buffer-local binding is in effect, the new value goes in that binding, so its other bindings are unchanged. This means that the change is visible only in the buffer where you made it.
The variable's ordinary binding, which is not associated with any specific buffer, is called the default binding. In most cases, this is the global binding.
A variable can have buffer-local bindings in some buffers but not in other buffers. The default binding is shared by all the buffers that don't have their own bindings for the variable. (This includes all newly-created buffers.) If you set the variable in a buffer that does not have a buffer-local binding for it, this sets the default binding, so the new value is visible in all the buffers that see the default binding.
The most common use of buffer-local bindings is for major modes to change
variables that control the behavior of commands. For example, C mode and
Lisp mode both set the variable paragraph-start to specify that only
blank lines separate paragraphs. They do this by making the variable
buffer-local in the buffer that is being put into C mode or Lisp mode, and
then setting it to the new value for that mode. See Major Modes.
The usual way to make a buffer-local binding is with
make-local-variable, which is what major mode commands typically
use. This affects just the current buffer; all other buffers (including
those yet to be created) will continue to share the default value unless
they are explicitly given their own buffer-local bindings.
A more powerful operation is to mark the variable as
automatically buffer-local by calling
make-variable-buffer-local. You can think of this as making the
variable local in all buffers, even those yet to be created. More
precisely, the effect is that setting the variable automatically makes
the variable local to the current buffer if it is not already so. All
buffers start out by sharing the default value of the variable as usual,
but setting the variable creates a buffer-local binding for the current
buffer. The new value is stored in the buffer-local binding, leaving
the default binding untouched. This means that the default value cannot
be changed with setq in any buffer; the only way to change it is
with setq-default.
Warning: When a variable has buffer-local
bindings in one or more buffers, let rebinds the binding that's
currently in effect. For instance, if the current buffer has a
buffer-local value, let temporarily rebinds that. If no
buffer-local bindings are in effect, let rebinds
the default value. If inside the let you then change to a
different current buffer in which a different binding is in effect,
you won't see the let binding any more. And if you exit the
let while still in the other buffer, you won't see the
unbinding occur (though it will occur properly). Here is an example
to illustrate:
(setq foo 'g)
(set-buffer "a")
(make-local-variable 'foo)
(setq foo 'a)
(let ((foo 'temp))
;; foo => 'temp ; let binding in buffer `a'
(set-buffer "b")
;; foo => 'g ; the global value since foo is not local in `b'
body...)
foo => 'g ; exiting restored the local value in buffer `a',
; but we don't see that in buffer `b'
(set-buffer "a") ; verify the local value was restored
foo => 'a
Note that references to foo in body access the
buffer-local binding of buffer `b'.
When a file specifies local variable values, these become buffer-local values when you visit the file. See File Variables.
A buffer-local variable cannot be made terminal-local (see Multiple Terminals).
This function creates a buffer-local binding in the current buffer for variable (a symbol). Other buffers are not affected. The value returned is variable.
The buffer-local value of variable starts out as the same value variable previously had. If variable was void, it remains void.
;; In buffer `b1': (setq foo 5) ; Affects all buffers. => 5 (make-local-variable 'foo) ; Now it is local in `b1'. => foo foo ; That did not change => 5 ; the value. (setq foo 6) ; Change the value => 6 ; in `b1'. foo => 6 ;; In buffer `b2', the value hasn't changed. (with-current-buffer "b2" foo) => 5Making a variable buffer-local within a
let-binding for that variable does not work reliably, unless the buffer in which you do this is not current either on entry to or exit from thelet. This is becauseletdoes not distinguish between different kinds of bindings; it knows only which variable the binding was made for.If the variable is terminal-local (see Multiple Terminals), this function signals an error. Such variables cannot have buffer-local bindings as well.
Warning: do not use
make-local-variablefor a hook variable. The hook variables are automatically made buffer-local as needed if you use the local argument toadd-hookorremove-hook.
This macro creates a buffer-local binding in the current buffer for variable, and gives it the buffer-local value value. It is equivalent to calling
make-local-variablefollowed bysetq. variable should be an unquoted symbol.
This function marks variable (a symbol) automatically buffer-local, so that any subsequent attempt to set it will make it local to the current buffer at the time. Unlike
make-local-variable, with which it is often confused, this cannot be undone, and affects the behavior of the variable in all buffers.A peculiar wrinkle of this feature is that binding the variable (with
letor other binding constructs) does not create a buffer-local binding for it. Only setting the variable (withsetorsetq), while the variable does not have alet-style binding that was made in the current buffer, does so.If variable does not have a default value, then calling this command will give it a default value of
nil. If variable already has a default value, that value remains unchanged. Subsequently callingmakunboundon variable will result in a void buffer-local value and leave the default value unaffected.The value returned is variable.
Warning: Don't assume that you should use
make-variable-buffer-localfor user-option variables, simply because users might want to customize them differently in different buffers. Users can make any variable local, when they wish to. It is better to leave the choice to them.The time to use
make-variable-buffer-localis when it is crucial that no two buffers ever share the same binding. For example, when a variable is used for internal purposes in a Lisp program which depends on having separate values in separate buffers, then usingmake-variable-buffer-localcan be the best solution.
This macro defines variable as a variable with initial value value and docstring, and marks it as automatically buffer-local. It is equivalent to calling
defvarfollowed bymake-variable-buffer-local. variable should be an unquoted symbol.
This returns
tif variable is buffer-local in buffer buffer (which defaults to the current buffer); otherwise,nil.
This returns
tif variable either has a buffer-local value in buffer buffer, or is automatically buffer-local. Otherwise, it returnsnil. If omitted ornil, buffer defaults to the current buffer.
This function returns the buffer-local binding of variable (a symbol) in buffer buffer. If variable does not have a buffer-local binding in buffer buffer, it returns the default value (see Default Value) of variable instead.
This function returns a list describing the buffer-local variables in buffer buffer. (If buffer is omitted, the current buffer is used.) Normally, each list element has the form
(sym.val), where sym is a buffer-local variable (a symbol) and val is its buffer-local value. But when a variable's buffer-local binding in buffer is void, its list element is just sym.(make-local-variable 'foobar) (makunbound 'foobar) (make-local-variable 'bind-me) (setq bind-me 69) (setq lcl (buffer-local-variables)) ;; First, built-in variables local in all buffers: => ((mark-active . nil) (buffer-undo-list . nil) (mode-name . "Fundamental") ... ;; Next, non-built-in buffer-local variables. ;; This one is buffer-local and void: foobar ;; This one is buffer-local and nonvoid: (bind-me . 69))Note that storing new values into the cdrs of cons cells in this list does not change the buffer-local values of the variables.
This function deletes the buffer-local binding (if any) for variable (a symbol) in the current buffer. As a result, the default binding of variable becomes visible in this buffer. This typically results in a change in the value of variable, since the default value is usually different from the buffer-local value just eliminated.
If you kill the buffer-local binding of a variable that automatically becomes buffer-local when set, this makes the default value visible in the current buffer. However, if you set the variable again, that will once again create a buffer-local binding for it.
kill-local-variablereturns variable.This function is a command because it is sometimes useful to kill one buffer-local variable interactively, just as it is useful to create buffer-local variables interactively.
This function eliminates all the buffer-local variable bindings of the current buffer except for variables marked as permanent and local hook functions that have a non-
nilpermanent-local-hookproperty (see Setting Hooks). As a result, the buffer will see the default values of most variables.This function also resets certain other information pertaining to the buffer: it sets the local keymap to
nil, the syntax table to the value of(standard-syntax-table), the case table to(standard-case-table), and the abbrev table to the value offundamental-mode-abbrev-table.The very first thing this function does is run the normal hook
change-major-mode-hook(see below).Every major mode command begins by calling this function, which has the effect of switching to Fundamental mode and erasing most of the effects of the previous major mode. To ensure that this does its job, the variables that major modes set should not be marked permanent.
kill-all-local-variablesreturnsnil.
The function
kill-all-local-variablesruns this normal hook before it does anything else. This gives major modes a way to arrange for something special to be done if the user switches to a different major mode. It is also useful for buffer-specific minor modes that should be forgotten if the user changes the major mode.For best results, make this variable buffer-local, so that it will disappear after doing its job and will not interfere with the subsequent major mode. See Hooks.
A buffer-local variable is permanent if the variable name (a
symbol) has a permanent-local property that is non-nil.
Such variables are unaffected by kill-all-local-variables, and
their local bindings are therefore not cleared by changing major modes.
Permanent locals are appropriate for data pertaining to where the file
came from or how to save it, rather than with how to edit the contents.
The global value of a variable with buffer-local bindings is also called the default value, because it is the value that is in effect whenever neither the current buffer nor the selected frame has its own binding for the variable.
The functions default-value and setq-default access and
change a variable's default value regardless of whether the current
buffer has a buffer-local binding. For example, you could use
setq-default to change the default setting of
paragraph-start for most buffers; and this would work even when
you are in a C or Lisp mode buffer that has a buffer-local value for
this variable.
The special forms defvar and defconst also set the
default value (if they set the variable at all), rather than any
buffer-local value.
This function returns symbol's default value. This is the value that is seen in buffers and frames that do not have their own values for this variable. If symbol is not buffer-local, this is equivalent to
symbol-value(see Accessing Variables).
The function
default-boundptells you whether symbol's default value is nonvoid. If(default-boundp 'foo)returnsnil, then(default-value 'foo)would get an error.
default-boundpis todefault-valueasboundpis tosymbol-value.
This special form gives each symbol a new default value, which is the result of evaluating the corresponding form. It does not evaluate symbol, but does evaluate form. The value of the
setq-defaultform is the value of the last form.If a symbol is not buffer-local for the current buffer, and is not marked automatically buffer-local,
setq-defaulthas the same effect assetq. If symbol is buffer-local for the current buffer, then this changes the value that other buffers will see (as long as they don't have a buffer-local value), but not the value that the current buffer sees.;; In buffer `foo': (make-local-variable 'buffer-local) => buffer-local (setq buffer-local 'value-in-foo) => value-in-foo (setq-default buffer-local 'new-default) => new-default buffer-local => value-in-foo (default-value 'buffer-local) => new-default ;; In (the new) buffer `bar': buffer-local => new-default (default-value 'buffer-local) => new-default (setq buffer-local 'another-default) => another-default (default-value 'buffer-local) => another-default ;; Back in buffer `foo': buffer-local => value-in-foo (default-value 'buffer-local) => another-default
This function is like
setq-default, except that symbol is an ordinary evaluated argument.(set-default (car '(a b c)) 23) => 23 (default-value 'a) => 23
A file can specify local variable values; Emacs uses these to create buffer-local bindings for those variables in the buffer visiting that file. See Local Variables in Files, for basic information about file-local variables. This section describes the functions and variables that affect how file-local variables are processed.
If a file-local variable could specify an arbitrary function or Lisp expression that would be called later, visiting a file could take over your Emacs. Emacs protects against this by automatically setting only those file-local variables whose specified values are known to be safe. Other file-local variables are set only if the user agrees.
For additional safety, read-circle is temporarily bound to
nil when Emacs reads file-local variables (see Input Functions). This prevents the Lisp reader from recognizing circular
and shared Lisp structures (see Circular Objects).
This variable controls whether to process file-local variables. The possible values are:
t(the default)- Set the safe variables, and query (once) about any unsafe variables.
:safe- Set only the safe variables and do not query.
:all- Set all the variables and do not query.
nil- Don't set any variables.
- anything else
- Query (once) about all the variables.
This is a list of regular expressions. If a file has a name matching an element of this list, then it is not scanned for any form of file-local variable. For examples of why you might want to use this, see Auto Major Mode.
This function parses, and binds or evaluates as appropriate, any local variables specified by the contents of the current buffer. The variable
enable-local-variableshas its effect here. However, this function does not look for the `mode:' local variable in the `-*-' line.set-auto-modedoes that, also takingenable-local-variablesinto account (see Auto Major Mode).This function works by walking the alist stored in
file-local-variables-alistand applying each local variable in turn. It callsbefore-hack-local-variables-hookandhack-local-variables-hookbefore and after applying the variables, respectively. It only calls the before-hook if the alist is non-nil; it always calls the other hook. This function ignores a `mode' element if it specifies the same major mode as the buffer already has.If the optional argument mode-only is non-
nil, then all this function does is return a symbol specifying the major mode, if the `-*-' line or the local variables list specifies one, andnilotherwise. It does not set the mode nor any other file-local variable.
This buffer-local variable holds the alist of file-local variable settings. Each element of the alist is of the form
(var.value), where var is a symbol of the local variable and value is its value. When Emacs visits a file, it first collects all the file-local variables into this alist, and then thehack-local-variablesfunction applies them one by one.
Emacs calls this hook immediately before applying file-local variables stored in
file-local-variables-alist.
Emacs calls this hook immediately after it finishes applying file-local variables stored in
file-local-variables-alist.
You can specify safe values for a variable with a
safe-local-variable property. The property has to be a
function of one argument; any value is safe if the function returns
non-nil given that value. Many commonly-encountered file
variables have safe-local-variable properties; these include
fill-column, fill-prefix, and indent-tabs-mode.
For boolean-valued variables that are safe, use booleanp as the
property value.
When defining a user option using defcustom, you can set its
safe-local-variable property by adding the arguments
:safe function to defcustom (see Variable Definitions).
This variable provides another way to mark some variable values as safe. It is a list of cons cells
(var.val), where var is a variable name and val is a value which is safe for that variable.When Emacs asks the user whether or not to obey a set of file-local variable specifications, the user can choose to mark them as safe. Doing so adds those variable/value pairs to
safe-local-variable-values, and saves it to the user's custom file.
This function returns non-
nilif it is safe to give sym the value val, based on the above criteria.
Some variables are considered risky. If a variable is risky,
it is never entered automatically into
safe-local-variable-values; Emacs always queries before setting
a risky variable, unless the user explicitly allows a value by
customizing safe-local-variable-values directly.
Any variable whose name has a non-nil
risky-local-variable property is considered risky. When you
define a user option using defcustom, you can set its
risky-local-variable property by adding the arguments
:risky value to defcustom (see Variable Definitions). In addition, any variable whose name ends in any of
`-command', `-frame-alist', `-function',
`-functions', `-hook', `-hooks', `-form',
`-forms', `-map', `-map-alist', `-mode-alist',
`-program', or `-predicate' is automatically considered
risky. The variables `font-lock-keywords',
`font-lock-keywords' followed by a digit, and
`font-lock-syntactic-keywords' are also considered risky.
This function returns non-
nilif sym is a risky variable, based on the above criteria.
This variable holds a list of variables that should not be given local values by files. Any value specified for one of these variables is completely ignored.
The `Eval:' “variable” is also a potential loophole, so Emacs normally asks for confirmation before handling it.
This variable controls processing of `Eval:' in `-*-' lines or local variables lists in files being visited. A value of
tmeans process them unconditionally;nilmeans ignore them; anything else means ask the user what to do for each file. The default value ismaybe.
This variable holds a list of expressions that are safe to evaluate when found in the `Eval:' “variable” in a file local variables list.
If the expression is a function call and the function has a
safe-local-eval-function property, the property value
determines whether the expression is safe to evaluate. The property
value can be a predicate to call to test the expression, a list of
such predicates (it's safe if any predicate succeeds), or t
(always safe provided the arguments are constant).
Text properties are also potential loopholes, since their values could include functions to call. So Emacs discards all text properties from string values specified for file-local variables.
A directory can specify local variable values common to all files in that directory; Emacs uses these to create buffer-local bindings for those variables in buffers visiting any file in that directory. This is useful when the files in the directory belong to some project and therefore share the same local variables.
There are two different methods for specifying directory local variables: by putting them in a special file, or by defining a project class for that directory.
This constant is the name of the file where Emacs expects to find the directory-local variables. The name of the file is .dir-locals.el8. A file by that name in a directory causes Emacs to apply its settings to any file in that directory or any of its subdirectories (optionally, you can exclude subdirectories; see below). If some of the subdirectories have their own .dir-locals.el files, Emacs uses the settings from the deepest file it finds starting from the file's directory and moving up the directory tree. The file specifies local variables as a specially formatted list; see Per-directory Local Variables, for more details.
This function reads the
.dir-locals.elfile and stores the directory-local variables infile-local-variables-alistthat is local to the buffer visiting any file in the directory, without applying them. It also stores the directory-local settings indir-locals-class-alist, where it defines a special class for the directory in which .dir-locals.el file was found. This function works by callingdir-locals-set-class-variablesanddir-locals-set-directory-class, described below.
This function looks for directory-local variables, and immediately applies them in the current buffer. It is intended to be called in the mode commands for non-file buffers, such as Dired buffers, to let them obey directory-local variable settings. For non-file buffers, Emacs looks for directory-local variables in
default-directoryand its parent directories.
This function defines a set of variable settings for the named class, which is a symbol. You can later assign the class to one or more directories, and Emacs will apply those variable settings to all files in those directories. The list in variables can be of one of the two forms:
(major-mode.alist)or(directory.list). With the first form, if the file's buffer turns on a mode that is derived from major-mode, then the all the variables in the associated alist are applied; alist should be of the form(name.value). A special valuenilfor major-mode means the settings are applicable to any mode. In alist, you can use a special name:subdirs. If the associated value isnil, the alist is only applied to files in the relevant directory, not to those in any subdirectories.With the second form of variables, if directory is the initial substring of the file's directory, then list is applied recursively by following the above rules; list should be of one of the two forms accepted by this function in variables.
This function assigns class to all the files in
directoryand its subdirectories. Thereafter, all the variable settings specified for class will be applied to any visited file in directory and its children. class must have been already defined bydir-locals-set-class-variables.Emacs uses this function internally when it loads directory variables from a
.dir-locals.elfile. In that case, the optional argument mtime holds the file modification time (as returned byfile-attributes). Emacs uses this time to check stored local variables are still valid. If you are assigning a class directly, not via a file, this argument should benil.
This alist holds the class symbols and the associated variable settings. It is updated by
dir-locals-set-class-variables.
This alist holds directory names, their assigned class names, and modification times of the associated directory local variables file (if there is one). The function
dir-locals-set-directory-classupdates this list.
If
nil, directory-local variables are ignored. This variable may be useful for modes that want to ignore directory-locals while still respecting file-local variables (see File Local Variables).
It is sometimes useful to make two variables synonyms, so that both
variables always have the same value, and changing either one also
changes the other. Whenever you change the name of a
variable—either because you realize its old name was not well
chosen, or because its meaning has partly changed—it can be useful
to keep the old name as an alias of the new one for
compatibility. You can do this with defvaralias.
This function defines the symbol new-alias as a variable alias for symbol base-variable. This means that retrieving the value of new-alias returns the value of base-variable, and changing the value of new-alias changes the value of base-variable. The two aliased variable names always share the same value and the same bindings.
If the docstring argument is non-
nil, it specifies the documentation for new-alias; otherwise, the alias gets the same documentation as base-variable has, if any, unless base-variable is itself an alias, in which case new-alias gets the documentation of the variable at the end of the chain of aliases.This function returns base-variable.
Variable aliases are convenient for replacing an old name for a
variable with a new name. make-obsolete-variable declares that
the old name is obsolete and therefore that it may be removed at some
stage in the future.
This function makes the byte compiler warn that the variable obsolete-name is obsolete. If current-name is a symbol, it is the variable's new name; then the warning message says to use current-name instead of obsolete-name. If current-name is a string, this is the message and there is no replacement variable. when should be a string indicating when the variable was first made obsolete (usually a version number string).
The optional argument access-type, if non-
nil, should specify the kind of access that will trigger obsolescence warnings; it can be eithergetorset.
You can make two variables synonyms and declare one obsolete at the
same time using the macro define-obsolete-variable-alias.
This macro marks the variable obsolete-name as obsolete and also makes it an alias for the variable current-name. It is equivalent to the following:
(defvaralias obsolete-name current-name docstring) (make-obsolete-variable obsolete-name current-name when)
This function returns the variable at the end of the chain of aliases of variable. If variable is not a symbol, or if variable is not defined as an alias, the function returns variable.
This function signals a
cyclic-variable-indirectionerror if there is a loop in the chain of symbols.
(defvaralias 'foo 'bar)
(indirect-variable 'foo)
=> bar
(indirect-variable 'bar)
=> bar
(setq bar 2)
bar
=> 2
foo
=> 2
(setq foo 0)
bar
=> 0
foo
=> 0
Ordinary Lisp variables can be assigned any value that is a valid
Lisp object. However, certain Lisp variables are not defined in Lisp,
but in C. Most of these variables are defined in the C code using
DEFVAR_LISP. Like variables defined in Lisp, these can take on
any value. However, some variables are defined using
DEFVAR_INT or DEFVAR_BOOL. See Writing Emacs Primitives, in particular the
description of functions of the type syms_of_filename,
for a brief discussion of the C implementation.
Variables of type DEFVAR_BOOL can only take on the values
nil or t. Attempting to assign them any other value
will set them to t:
(let ((display-hourglass 5))
display-hourglass)
=> t
Variables of type DEFVAR_INT can take on only integer values.
Attempting to assign them any other value will result in an error:
(setq undo-limit 1000.0)
error--> Wrong type argument: integerp, 1000.0
A generalized variable or place form is one of the many places in Lisp memory where values can be stored. The simplest place form is a regular Lisp variable. But the cars and cdrs of lists, elements of arrays, properties of symbols, and many other locations are also places where Lisp values are stored.
Generalized variables are analogous to lvalues in the C
language, where `x = a[i]' gets an element from an array
and `a[i] = x' stores an element using the same notation.
Just as certain forms like a[i] can be lvalues in C, there
is a set of forms that can be generalized variables in Lisp.
setf MacroThe setf macro is the most basic way to operate on generalized
variables. The setf form is like setq, except that it
accepts arbitrary place forms on the left side rather than just
symbols. For example, (setf (car a) b) sets the car of
a to b, doing the same operation as (setcar a b),
but without having to remember two separate functions for setting and
accessing every type of place.
This macro evaluates form and stores it in place, which must be a valid generalized variable form. If there are several place and form pairs, the assignments are done sequentially just as with
setq.setfreturns the value of the last form.
The following Lisp forms will work as generalized variables, and
so may appear in the place argument of setf:
(setf x y) is
exactly equivalent to (setq x y), and setq itself is
strictly speaking redundant given that setf exists. Many
programmers continue to prefer setq for setting simple
variables, though, purely for stylistic or historical reasons.
The macro (setf x y) actually expands to (setq x y),
so there is no performance penalty for using it in compiled code.
aref cddr symbol-function
car elt symbol-plist
caar get symbol-value
cadr gethash
cdr nth
cdar nthcdr
alist-get process-get
frame-parameter process-sentinel
terminal-parameter window-buffer
keymap-parent window-display-table
match-data window-dedicated-p
overlay-get window-hscroll
overlay-start window-parameter
overlay-end window-point
process-buffer window-start
process-filter default-value
setf signals an error if you pass a place form that it
does not know how to handle.
Note that for nthcdr, the list argument of the function must
itself be a valid place form. For example, (setf (nthcdr
0 foo) 7) will set foo itself to 7.
The macros push (see List Variables) and pop
(see List Elements) can manipulate generalized variables,
not just lists. (pop place) removes and returns the first
element of the list stored in place. It is analogous to
(prog1 (car place) (setf place (cdr place))),
except that it takes care to evaluate all subforms only once.
(push x place) inserts x at the front of
the list stored in place. It is analogous to (setf
place (cons x place)), except for evaluation of the
subforms. Note that push and pop on an nthcdr
place can be used to insert or delete at any position in a list.
The cl-lib library defines various extensions for generalized
variables, including additional setf places.
See Generalized Variables.
setf formsThis section describes how to define new forms that setf can
operate on.
This macro enables you to easily define
setfmethods for simple cases. name is the name of a function, macro, or special form. You can use this macro whenever name has a directly corresponding setter function that updates it, e.g.,(gv-define-simple-setter car setcar).This macro translates a call of the form
(setf (name args...) value)into
(setter args... value)Such a
setfcall is documented to return value. This is no problem with, e.g.,carandsetcar, becausesetcarreturns the value that it set. If your setter function does not return value, use a non-nilvalue for the fix-return argument ofgv-define-simple-setter. This expands into something equivalent to(let ((temp value)) (setter args... temp) temp)so ensuring that it returns the correct result.
This macro allows for more complex
setfexpansions than the previous form. You may need to use this form, for example, if there is no simple setter function to call, or if there is one but it requires different arguments to the place form.This macro expands the form
(setf (name args...)value)by first binding thesetfargument forms(value args...)according to arglist, and then executing body. body should return a Lisp form that does the assignment, and finally returns the value that was set. An example of using this macro is:(gv-define-setter caar (val x) `(setcar (car ,x) ,val))
For more control over the expansion, see the macro gv-define-expander.
The macro gv-letplace can be useful in defining macros that
perform similarly to setf; for example, the incf macro
of Common Lisp. Consult the source file gv.el for more details.
Common Lisp note: Common Lisp defines another way to specify thesetfbehavior of a function, namelysetffunctions, whose names are lists(setfname)rather than symbols. For example,(defun (setf foo) ...)defines the function that is used whensetfis applied tofoo. Emacs does not support this. It is a compile-time error to usesetfon a form that has not already had an appropriate expansion defined. In Common Lisp, this is not an error since the function(setffunc)might be defined later.
A Lisp program is composed mainly of Lisp functions. This chapter explains what functions are, how they accept arguments, and how to define them.
In a general sense, a function is a rule for carrying out a computation given input values called arguments. The result of the computation is called the value or return value of the function. The computation can also have side effects, such as lasting changes in the values of variables or the contents of data structures.
In most computer languages, every function has a name. But in Lisp,
a function in the strictest sense has no name: it is an object which
can optionally be associated with a symbol (e.g., car)
that serves as the function name. See Function Names. When a
function has been given a name, we usually also refer to that symbol
as a “function” (e.g., we refer to “the function car”).
In this manual, the distinction between a function name and the
function object itself is usually unimportant, but we will take note
wherever it is relevant.
Certain function-like objects, called special forms and macros, also accept arguments to carry out computations. However, as explained below, these are not considered functions in Emacs Lisp.
Here are important terms for functions and function-like objects:
car and append. In
addition, all special forms (see below) are also considered
primitives.
Usually, a function is implemented as a primitive because it is a
fundamental part of Lisp (e.g., car), or because it provides a
low-level interface to operating system services, or because it needs
to run fast. Unlike functions defined in Lisp, primitives can be
modified or added only by changing the C sources and recompiling
Emacs. See Writing Emacs Primitives.
if, and, and while.
See Special Forms.
command-execute
primitive, usually due to the user typing in a key sequence
bound to that command. See Interactive Call. A command is
usually a function; if the function is written in Lisp, it is made
into a command by an interactive form in the function
definition (see Defining Commands). Commands that are functions
can also be called from Lisp expressions, just like other functions.
Keyboard macros (strings and vectors) are commands also, even though
they are not functions. See Keyboard Macros. We say that a symbol
is a command if its function cell contains a command (see Symbol Components); such a named command can be invoked with
M-x.
You can use the function functionp to test if an object is a
function:
This function returns
tif object is any kind of function, i.e., can be passed tofuncall. Note thatfunctionpreturnstfor symbols that are function names, and returnsnilfor special forms.
Unlike functionp, the next three functions do not treat
a symbol as its function definition.
This function returns
tif object is a built-in function (i.e., a Lisp primitive).(subrp 'message) ;messageis a symbol, => nil ; not a subr object. (subrp (symbol-function 'message)) => t
This function returns
tif object is a byte-code function. For example:(byte-code-function-p (symbol-function 'next-line)) => t
This function provides information about the argument list of a primitive, subr. The returned value is a pair
(min.max). min is the minimum number of args. max is the maximum number or the symbolmany, for a function with&restarguments, or the symbolunevalledif subr is a special form.
A lambda expression is a function object written in Lisp. Here is an example:
(lambda (x)
"Return the hyperbolic cosine of X."
(* 0.5 (+ (exp x) (exp (- x)))))
In Emacs Lisp, such a list is a valid expression which evaluates to a function object.
A lambda expression, by itself, has no name; it is an anonymous function. Although lambda expressions can be used this way (see Anonymous Functions), they are more commonly associated with symbols to make named functions (see Function Names). Before going into these details, the following subsections describe the components of a lambda expression and what they do.
A lambda expression is a list that looks like this:
(lambda (arg-variables...)
[documentation-string]
[interactive-declaration]
body-forms...)
The first element of a lambda expression is always the symbol
lambda. This indicates that the list represents a function. The
reason functions are defined to start with lambda is so that
other lists, intended for other uses, will not accidentally be valid as
functions.
The second element is a list of symbols—the argument variable names. This is called the lambda list. When a Lisp function is called, the argument values are matched up against the variables in the lambda list, which are given local bindings with the values provided. See Local Variables.
The documentation string is a Lisp string object placed within the function definition to describe the function for the Emacs help facilities. See Function Documentation.
The interactive declaration is a list of the form (interactive
code-string). This declares how to provide arguments if the
function is used interactively. Functions with this declaration are called
commands; they can be called using M-x or bound to a key.
Functions not intended to be called in this way should not have interactive
declarations. See Defining Commands, for how to write an interactive
declaration.
The rest of the elements are the body of the function: the Lisp code to do the work of the function (or, as a Lisp programmer would say, “a list of Lisp forms to evaluate”). The value returned by the function is the value returned by the last element of the body.
Consider the following example:
(lambda (a b c) (+ a b c))
We can call this function by passing it to funcall, like this:
(funcall (lambda (a b c) (+ a b c))
1 2 3)
This call evaluates the body of the lambda expression with the variable
a bound to 1, b bound to 2, and c bound to 3.
Evaluation of the body adds these three numbers, producing the result 6;
therefore, this call to the function returns the value 6.
Note that the arguments can be the results of other function calls, as in this example:
(funcall (lambda (a b c) (+ a b c))
1 (* 2 3) (- 5 4))
This evaluates the arguments 1, (* 2 3), and (- 5
4) from left to right. Then it applies the lambda expression to the
argument values 1, 6 and 1 to produce the value 8.
As these examples show, you can use a form with a lambda expression
as its car to make local variables and give them values. In the
old days of Lisp, this technique was the only way to bind and
initialize local variables. But nowadays, it is clearer to use the
special form let for this purpose (see Local Variables).
Lambda expressions are mainly used as anonymous functions for passing
as arguments to other functions (see Anonymous Functions), or
stored as symbol function definitions to produce named functions
(see Function Names).
Our simple sample function, (lambda (a b c) (+ a b c)),
specifies three argument variables, so it must be called with three
arguments: if you try to call it with only two arguments or four
arguments, you get a wrong-number-of-arguments error.
It is often convenient to write a function that allows certain
arguments to be omitted. For example, the function substring
accepts three arguments—a string, the start index and the end
index—but the third argument defaults to the length of the
string if you omit it. It is also convenient for certain functions to
accept an indefinite number of arguments, as the functions list
and + do.
To specify optional arguments that may be omitted when a function
is called, simply include the keyword &optional before the optional
arguments. To specify a list of zero or more extra arguments, include the
keyword &rest before one final argument.
Thus, the complete syntax for an argument list is as follows:
(required-vars...
[&optional optional-vars...]
[&rest rest-var])
The square brackets indicate that the &optional and &rest
clauses, and the variables that follow them, are optional.
A call to the function requires one actual argument for each of the
required-vars. There may be actual arguments for zero or more of
the optional-vars, and there cannot be any actual arguments beyond
that unless the lambda list uses &rest. In that case, there may
be any number of extra actual arguments.
If actual arguments for the optional and rest variables are omitted,
then they always default to nil. There is no way for the
function to distinguish between an explicit argument of nil and
an omitted argument. However, the body of the function is free to
consider nil an abbreviation for some other meaningful value.
This is what substring does; nil as the third argument to
substring means to use the length of the string supplied.
Common Lisp note: Common Lisp allows the function to specify what default value to use when an optional argument is omitted; Emacs Lisp always usesnil. Emacs Lisp does not supportsupplied-pvariables that tell you whether an argument was explicitly passed.
For example, an argument list that looks like this:
(a b &optional c d &rest e)
binds a and b to the first two actual arguments, which are
required. If one or two more arguments are provided, c and
d are bound to them respectively; any arguments after the first
four are collected into a list and e is bound to that list. If
there are only two arguments, c is nil; if two or three
arguments, d is nil; if four arguments or fewer, e
is nil.
There is no way to have required arguments following optional
ones—it would not make sense. To see why this must be so, suppose
that c in the example were optional and d were required.
Suppose three actual arguments are given; which variable would the
third argument be for? Would it be used for the c, or for
d? One can argue for both possibilities. Similarly, it makes
no sense to have any more arguments (either required or optional)
after a &rest argument.
Here are some examples of argument lists and proper calls:
(funcall (lambda (n) (1+ n)) ; One required: 1) ; requires exactly one argument. => 2 (funcall (lambda (n &optional n1) ; One required and one optional: (if n1 (+ n n1) (1+ n))) ; 1 or 2 arguments. 1 2) => 3 (funcall (lambda (n &rest ns) ; One required and one rest: (+ n (apply '+ ns))) ; 1 or more arguments. 1 2 3 4 5) => 15
A lambda expression may optionally have a documentation string just after the lambda list. This string does not affect execution of the function; it is a kind of comment, but a systematized comment which actually appears inside the Lisp world and can be used by the Emacs help facilities. See Documentation, for how the documentation string is accessed.
It is a good idea to provide documentation strings for all the functions in your program, even those that are called only from within your program. Documentation strings are like comments, except that they are easier to access.
The first line of the documentation string should stand on its own,
because apropos displays just this first line. It should consist
of one or two complete sentences that summarize the function's purpose.
The start of the documentation string is usually indented in the source file, but since these spaces come before the starting double-quote, they are not part of the string. Some people make a practice of indenting any additional lines of the string so that the text lines up in the program source. That is a mistake. The indentation of the following lines is inside the string; what looks nice in the source code will look ugly when displayed by the help commands.
You may wonder how the documentation string could be optional, since there are required components of the function that follow it (the body). Since evaluation of a string returns that string, without any side effects, it has no effect if it is not the last form in the body. Thus, in practice, there is no confusion between the first form of the body and the documentation string; if the only body form is a string then it serves both as the return value and as the documentation.
The last line of the documentation string can specify calling conventions different from the actual function arguments. Write text like this:
\(fn arglist)
following a blank line, at the beginning of the line, with no newline following it inside the documentation string. (The `\' is used to avoid confusing the Emacs motion commands.) The calling convention specified in this way appears in help messages in place of the one derived from the actual arguments of the function.
This feature is particularly useful for macro definitions, since the arguments written in a macro definition often do not correspond to the way users think of the parts of the macro call.
A symbol can serve as the name of a function. This happens when the symbol's function cell (see Symbol Components) contains a function object (e.g., a lambda expression). Then the symbol itself becomes a valid, callable function, equivalent to the function object in its function cell.
The contents of the function cell are also called the symbol's function definition. The procedure of using a symbol's function definition in place of the symbol is called symbol function indirection; see Function Indirection. If you have not given a symbol a function definition, its function cell is said to be void, and it cannot be used as a function.
In practice, nearly all functions have names, and are referred to by
their names. You can create a named Lisp function by defining a
lambda expression and putting it in a function cell (see Function Cells). However, it is more common to use the defun special
form, described in the next section.
See Defining Functions.
We give functions names because it is convenient to refer to them by their names in Lisp expressions. Also, a named Lisp function can easily refer to itself—it can be recursive. Furthermore, primitives can only be referred to textually by their names, since primitive function objects (see Primitive Function Type) have no read syntax.
A function need not have a unique name. A given function object
usually appears in the function cell of only one symbol, but
this is just a convention. It is easy to store it in several symbols
using fset; then each of the symbols is a valid name for the
same function.
Note that a symbol used as a function name may also be used as a variable; these two uses of a symbol are independent and do not conflict. (This is not the case in some dialects of Lisp, like Scheme.)
We usually give a name to a function when it is first created. This
is called defining a function, and it is done with the
defun macro.
defunis the usual way to define new Lisp functions. It defines the symbol name as a function with argument list args and body forms given by body. Neither name nor args should be quoted.doc, if present, should be a string specifying the function's documentation string (see Function Documentation). declare, if present, should be a
declareform specifying function metadata (see Declare Form). interactive, if present, should be aninteractiveform specifying how the function is to be called interactively (see Interactive Call).The return value of
defunis undefined.Here are some examples:
(defun foo () 5) (foo) => 5 (defun bar (a &optional b &rest c) (list a b c)) (bar 1 2 3 4 5) => (1 2 (3 4 5)) (bar 1) => (1 nil nil) (bar) error--> Wrong number of arguments. (defun capitalize-backwards () "Upcase the last letter of the word at point." (interactive) (backward-word 1) (forward-word 1) (backward-char 1) (capitalize-word 1))Be careful not to redefine existing functions unintentionally.
defunredefines even primitive functions such ascarwithout any hesitation or notification. Emacs does not prevent you from doing this, because redefining a function is sometimes done deliberately, and there is no way to distinguish deliberate redefinition from unintentional redefinition.
This function defines the symbol name as a function, with definition definition (which can be any valid Lisp function). Its return value is undefined.
If doc is non-
nil, it becomes the function documentation of name. Otherwise, any documentation provided by definition is used.Internally,
defaliasnormally usesfsetto set the definition. If name has adefalias-fset-functionproperty, however, the associated value is used as a function to call in place offset.The proper place to use
defaliasis where a specific function name is being defined—especially where that name appears explicitly in the source file being loaded. This is becausedefaliasrecords which file defined the function, just likedefun(see Unloading).By contrast, in programs that manipulate function definitions for other purposes, it is better to use
fset, which does not keep such records. See Function Cells.
You cannot create a new primitive function with defun or
defalias, but you can use them to change the function definition of
any symbol, even one such as car or x-popup-menu whose
normal definition is a primitive. However, this is risky: for
instance, it is next to impossible to redefine car without
breaking Lisp completely. Redefining an obscure function such as
x-popup-menu is less dangerous, but it still may not work as
you expect. If there are calls to the primitive from C code, they
call the primitive's C definition directly, so changing the symbol's
definition will have no effect on them.
See also defsubst, which defines a function like defun
and tells the Lisp compiler to perform inline expansion on it.
See Inline Functions.
Alternatively, you can define a function by providing the code which will inline it as a compiler macro. The following macros make this possible.
Define a function name by providing code that does its inlining, as a compiler macro. The function will accept the argument list args and will have the specified body.
If present, doc should be the function's documentation string (see Function Documentation); declare, if present, should be a
declareform (see Declare Form) specifying the function's metadata.
Functions defined via define-inline have several advantages
with respect to macros defined by defsubst or defmacro:
mapcar (see Mapping Functions).
cl-defsubst
(see Argument Lists).
Like defmacro, a function inlined with define-inline
inherits the scoping rules, either dynamic or lexical, from the call
site. See Variable Scoping.
The following macros should be used in the body of a function defined
by define-inline.
Quote expression for
define-inline. This is similar to the backquote (see Backquote), but quotes code and accepts only,, not,@.
This is is similar to
let(see Local Variables): it sets up local variables as specified by bindings, and then evaluates body with those bindings in effect. Each element of bindings should be either a symbol or a list of the form(varexpr); the result is to evaluate expr and bind var to the result. The tail of bindings can be eithernilor a symbol which should hold a list of arguments, in which case each argument is evaluated, and the symbol is bound to the resulting list.
Here's an example of using define-inline:
(define-inline myaccessor (obj)
(inline-letevals (obj)
(inline-quote (if (foo-p ,obj) (aref (cdr ,obj) 3) (aref ,obj 2)))))
This is equivalent to
(defsubst myaccessor (obj)
(if (foo-p obj) (aref (cdr obj) 3) (aref obj 2)))
Defining functions is only half the battle. Functions don't do anything until you call them, i.e., tell them to run. Calling a function is also known as invocation.
The most common way of invoking a function is by evaluating a list.
For example, evaluating the list (concat "a" "b") calls the
function concat with arguments "a" and "b".
See Evaluation, for a description of evaluation.
When you write a list as an expression in your program, you specify
which function to call, and how many arguments to give it, in the text
of the program. Usually that's just what you want. Occasionally you
need to compute at run time which function to call. To do that, use
the function funcall. When you also need to determine at run
time how many arguments to pass, use apply.
funcallcalls function with arguments, and returns whatever function returns.Since
funcallis a function, all of its arguments, including function, are evaluated beforefuncallis called. This means that you can use any expression to obtain the function to be called. It also means thatfuncalldoes not see the expressions you write for the arguments, only their values. These values are not evaluated a second time in the act of calling function; the operation offuncallis like the normal procedure for calling a function, once its arguments have already been evaluated.The argument function must be either a Lisp function or a primitive function. Special forms and macros are not allowed, because they make sense only when given the unevaluated argument expressions.
funcallcannot provide these because, as we saw above, it never knows them in the first place.If you need to use
funcallto call a command and make it behave as if invoked interactively, usefuncall-interactively(see Interactive Call).(setq f 'list) => list (funcall f 'x 'y 'z) => (x y z) (funcall f 'x 'y '(z)) => (x y (z)) (funcall 'and t nil) error--> Invalid function: #<subr and>Compare these examples with the examples of
apply.
applycalls function with arguments, just likefuncallbut with one difference: the last of arguments is a list of objects, which are passed to function as separate arguments, rather than a single list. We say thatapplyspreads this list so that each individual element becomes an argument.
applyreturns the result of calling function. As withfuncall, function must either be a Lisp function or a primitive function; special forms and macros do not make sense inapply.(setq f 'list) => list (apply f 'x 'y 'z) error--> Wrong type argument: listp, z (apply '+ 1 2 '(3 4)) => 10 (apply '+ '(1 2 3 4)) => 10 (apply 'append '((a b c) nil (x y z) nil)) => (a b c x y z)For an interesting example of using
apply, see Definition of mapcar.
Sometimes it is useful to fix some of the function's arguments at certain values, and leave the rest of arguments for when the function is actually called. The act of fixing some of the function's arguments is called partial application of the function9. The result is a new function that accepts the rest of arguments and calls the original function with all the arguments combined.
Here's how to do partial application in Emacs Lisp:
This function returns a new function which, when called, will call func with the list of arguments composed from args and additional arguments specified at the time of the call. If func accepts n arguments, then a call to
apply-partiallywith m<n arguments will produce a new function of n-m arguments.Here's how we could define the built-in function
1+, if it didn't exist, usingapply-partiallyand+, another built-in function:(defalias '1+ (apply-partially '+ 1) "Increment argument by one.") (1+ 10) => 11
It is common for Lisp functions to accept functions as arguments or
find them in data structures (especially in hook variables and property
lists) and call them using funcall or apply. Functions
that accept function arguments are often called functionals.
Sometimes, when you call a functional, it is useful to supply a no-op function as the argument. Here are two different kinds of no-op function:
Some functions are user-visible commands, which can be called
interactively (usually by a key sequence). It is possible to invoke
such a command exactly as though it was called interactively, by using
the call-interactively function. See Interactive Call.
A mapping function applies a given function (not a
special form or macro) to each element of a list or other collection.
Emacs Lisp has several such functions; this section describes
mapcar, mapc, and mapconcat, which map over a
list. See Definition of mapatoms, for the function mapatoms
which maps over the symbols in an obarray. See Definition of maphash, for the function maphash which maps over key/value
associations in a hash table.
These mapping functions do not allow char-tables because a char-table
is a sparse array whose nominal range of indices is very large. To map
over a char-table in a way that deals properly with its sparse nature,
use the function map-char-table (see Char-Tables).
mapcarapplies function to each element of sequence in turn, and returns a list of the results.The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string. The result is always a list. The length of the result is the same as the length of sequence. For example:
(mapcar 'car '((a b) (c d) (e f))) => (a c e) (mapcar '1+ [1 2 3]) => (2 3 4) (mapcar 'string "abc") => ("a" "b" "c") ;; Call each function inmy-hooks. (mapcar 'funcall my-hooks) (defun mapcar* (function &rest args) "Apply FUNCTION to successive cars of all ARGS. Return the list of results." ;; If no list is exhausted, (if (not (memq nil args)) ;; apply function to cars. (cons (apply function (mapcar 'car args)) (apply 'mapcar* function ;; Recurse for rest of elements. (mapcar 'cdr args))))) (mapcar* 'cons '(a b c) '(1 2 3 4)) => ((a . 1) (b . 2) (c . 3))
mapcis likemapcarexcept that function is used for side-effects only—the values it returns are ignored, not collected into a list.mapcalways returns sequence.
mapconcatapplies function to each element of sequence; the results, which must be sequences of characters (strings, vectors, or lists), are concatenated into a single string return value. Between each pair of result sequences,mapconcatinserts the characters from separator, which also must be a string, or a vector or list of characters. See Sequences Arrays Vectors.The argument function must be a function that can take one argument and returns a sequence of characters: a string, a vector, or a list. The argument sequence can be any kind of sequence except a char-table; that is, a list, a vector, a bool-vector, or a string.
(mapconcat 'symbol-name '(The cat in the hat) " ") => "The cat in the hat" (mapconcat (function (lambda (x) (format "%c" (1+ x)))) "HAL-8000" "") => "IBM.9111"
Although functions are usually defined with defun and given
names at the same time, it is sometimes convenient to use an explicit
lambda expression—an anonymous function. Anonymous functions
are valid wherever function names are. They are often assigned as
variable values, or as arguments to functions; for instance, you might
pass one as the function argument to mapcar, which
applies that function to each element of a list (see Mapping Functions). See describe-symbols example, for a realistic example
of this.
When defining a lambda expression that is to be used as an anonymous
function, you can in principle use any method to construct the list.
But typically you should use the lambda macro, or the
function special form, or the #' read syntax:
This macro returns an anonymous function with argument list args, documentation string doc (if any), interactive spec interactive (if any), and body forms given by body.
In effect, this macro makes
lambdaforms self-quoting: evaluating a form whose car islambdayields the form itself:(lambda (x) (* x x)) => (lambda (x) (* x x))The
lambdaform has one other effect: it tells the Emacs evaluator and byte-compiler that its argument is a function, by usingfunctionas a subroutine (see below).
This special form returns function-object without evaluating it. In this, it is similar to
quote(see Quoting). But unlikequote, it also serves as a note to the Emacs evaluator and byte-compiler that function-object is intended to be used as a function. Assuming function-object is a valid lambda expression, this has two effects:
- When the code is byte-compiled, function-object is compiled into a byte-code function object (see Byte Compilation).
- When lexical binding is enabled, function-object is converted into a closure. See Closures.
The read syntax #' is a short-hand for using function.
The following forms are all equivalent:
(lambda (x) (* x x))
(function (lambda (x) (* x x)))
#'(lambda (x) (* x x))
In the following example, we define a change-property
function that takes a function as its third argument, followed by a
double-property function that makes use of
change-property by passing it an anonymous function:
(defun change-property (symbol prop function)
(let ((value (get symbol prop)))
(put symbol prop (funcall function value))))
(defun double-property (symbol prop)
(change-property symbol prop (lambda (x) (* 2 x))))
Note that we do not quote the lambda form.
If you compile the above code, the anonymous function is also compiled. This would not happen if, say, you had constructed the anonymous function by quoting it as a list:
(defun double-property (symbol prop)
(change-property symbol prop '(lambda (x) (* 2 x))))
In that case, the anonymous function is kept as a lambda expression in
the compiled code. The byte-compiler cannot assume this list is a
function, even though it looks like one, since it does not know that
change-property intends to use it as a function.
Functions defined using defun have a hard-coded set of
assumptions about the types and expected values of their arguments.
For example, a function that was designed to handle values of its
argument that are either numbers or lists of numbers will fail or
signal an error if called with a value of any other type, such as a
vector or a string. This happens because the implementation of the
function is not prepared to deal with types other than those assumed
during the design.
By contrast, object-oriented programs use polymorphic functions: a set of specialized functions having the same name, each one of which was written for a certain specific set of argument types. Which of the functions is actually called is decided at run time based on the types of the actual arguments.
Emacs provides support for polymorphism. Like other Lisp environments, notably Common Lisp and its Common Lisp Object System (CLOS), this support is based on generic functions. The Emacs generic functions closely follow CLOS, including use of similar names, so if you have experience with CLOS, the rest of this section will sound very familiar.
A generic function specifies an abstract operation, by defining its
name and list of arguments, but (usually) no implementation. The
actual implementation for several specific classes of arguments is
provided by methods, which should be defined separately. Each
method that implements a generic function has the same name as the
generic function, but the method's definition indicates what kinds of
arguments it can handle by specializing the arguments defined by
the generic function. These argument specializers can be more
or less specific; for example, a string type is more specific
than a more general type, such as sequence.
Note that, unlike in message-based OO languages, such as C++ and Simula, methods that implement generic functions don't belong to a class, they belong to the generic function they implement.
When a generic function is invoked, it selects the applicable methods by comparing the actual arguments passed by the caller with the argument specializers of each method. A method is applicable if the actual arguments of the call are compatible with the method's specializers. If more than one method is applicable, they are combined using certain rules, described below, and the combination then handles the call.
This macro defines a generic function with the specified name and arguments. If body is present, it provides the default implementation. If documentation is present (it should always be), it specifies the documentation string for the generic function, in the form
(:documentationdocstring). The optional options-and-methods can be one of the following forms:
(declaredeclarations)- A declare form, as described in Declare Form.
(:argument-precedence-order &restargs)- This form affects the sorting order for combining applicable methods. Normally, when two methods are compared during combination, method arguments are examined left to right, and the first method whose argument specializer is more specific will come before the other one. The order defined by this form overrides that, and the arguments are examined according to their order in this form, and not left to right.
(:method [qualifiers...] args &rest body)- This form defines a method like
cl-defmethoddoes.
This macro defines a particular implementation for the generic function called name. The implementation code is given by body. If present, docstring is the documentation string for the method. The arguments list, which must be identical in all the methods that implement a generic function, and must match the argument list of that function, provides argument specializers of the form
(arg spec), where arg is the argument name as specified in thecl-defgenericcall, and spec is one of the following specializer forms:
- type
- This specializer requires the argument to be of the given type, one of the types from the type hierarchy described below.
(eqlobject)- This specializer requires the argument be
eqlto the given object.
(headobject)- The argument must be a cons cell whose
cariseqlto object.
- struct-tag
- The argument must be an instance of a class named struct-tag defined with
cl-defstruct(see Structures), or of one of its parent classes.Alternatively, the argument specializer can be of the form
&context (expr spec), in which case the value of expr must be compatible with the specializer provided by spec; spec can be any of the forms described above. In other words, this form of specializer uses the value of expr instead of arguments for the decision whether the method is applicable. For example,&context (overwrite-mode (eql t))will make the method compatible only whenoverwrite-modeis turned on.The type specializer,
(arg type), can specify one of the system types in the following list. When a parent type is specified, an argument whose type is any of its more specific child types, as well as grand-children, grand-grand-children, etc. will also be compatible.
integer- Parent type:
number.
numbernull- Parent type:
symbol
symbolstring- Parent type:
array.
array- Parent type:
sequence.
cons- Parent type:
list.
list- Parent type:
sequence.
markeroverlayfloat- Parent type:
number.
window-configurationprocesswindowsubrcompiled-functionbufferchar-table- Parent type:
array.
bool-vector- Parent type:
array.
vector- Parent type:
array.
framehash-tablefont-specfont-entityfont-objectThe optional qualifier allows combining several applicable methods. If it is not present, the defined method is a primary method, responsible for providing the primary implementation of the generic function for the specialized arguments. You can also define auxiliary methods, by using one of the following values as qualifier:
:before- This auxiliary method will run before the primary method. More accurately, all the
:beforemethods will run before the primary, in the most-specific-first order.
:after- This auxiliary method will run after the primary method. More accurately, all such methods will run after the primary, in the most-specific-last order.
:around- This auxiliary method will run instead of the primary method. The most specific of such methods will be run before any other method. Such methods normally use
cl-call-next-method, described below, to invoke the other auxiliary or primary methods.
:extrastring- This allows you to add more methods, distinguished by string, for the same specializers and qualifiers.
Each time a generic function is called, it builds the effective method which will handle this invocation by combining the applicable methods defined for the function. The process of finding the applicable methods and producing the effective method is called dispatch. The applicable methods are those all of whose specializers are compatible with the actual arguments of the call. Since all of the arguments must be compatible with the specializers, they all determine whether a method is applicable. Methods that explicitly specialize more than one argument are called multiple-dispatch methods.
The applicable methods are sorted into the order in which they will be
combined. The method whose left-most argument specializer is the most
specific one will come first in the order. (Specifying
:argument-precedence-order as part of cl-defmethod
overrides that, as described above.) If the method body calls
cl-call-next-method, the next most-specific method will run.
If there are applicable :around methods, the most-specific of
them will run first; it should call cl-call-next-method to run
any of the less specific :around methods. Next, the
:before methods run in the order of their specificity, followed
by the primary method, and lastly the :after methods in the
reverse order of their specificity.
When invoked from within the lexical body of a primary or an
:aroundauxiliary method, call the next applicable method for the same generic function. Normally, it is called with no arguments, which means to call the next applicable method with the same arguments that the calling method was invoked. Otherwise, the specified arguments are used instead.
This function, when called from within the lexical body of a primary or an
:aroundauxiliary method, returns non-nilif there is a next method to call.
The function definition of a symbol is the object stored in the function cell of the symbol. The functions described here access, test, and set the function cell of symbols.
See also the function indirect-function. See Definition of indirect-function.
This returns the object in the function cell of symbol. It does not check that the returned object is a legitimate function.
If the function cell is void, the return value is
nil. To distinguish between a function cell that is void and one set tonil, usefboundp(see below).(defun bar (n) (+ n 2)) (symbol-function 'bar) => (lambda (n) (+ n 2)) (fset 'baz 'bar) => bar (symbol-function 'baz) => bar
If you have never given a symbol any function definition, we say
that that symbol's function cell is void. In other words, the
function cell does not have any Lisp object in it. If you try to call
the symbol as a function, Emacs signals a void-function error.
Note that void is not the same as nil or the symbol
void. The symbols nil and void are Lisp objects,
and can be stored into a function cell just as any other object can be
(and they can be valid functions if you define them in turn with
defun). A void function cell contains no object whatsoever.
You can test the voidness of a symbol's function definition with
fboundp. After you have given a symbol a function definition, you
can make it void once more using fmakunbound.
This function returns
tif the symbol has an object in its function cell,nilotherwise. It does not check that the object is a legitimate function.
This function makes symbol's function cell void, so that a subsequent attempt to access this cell will cause a
void-functionerror. It returns symbol. (See alsomakunbound, in Void Variables.)(defun foo (x) x) (foo 1) =>1 (fmakunbound 'foo) => foo (foo 1) error--> Symbol's function definition is void: foo
This function stores definition in the function cell of symbol. The result is definition. Normally definition should be a function or the name of a function, but this is not checked. The argument symbol is an ordinary evaluated argument.
The primary use of this function is as a subroutine by constructs that define or alter functions, like
defunoradvice-add(see Advising Functions). You can also use it to give a symbol a function definition that is not a function, e.g., a keyboard macro (see Keyboard Macros):;; Define a named keyboard macro. (fset 'kill-two-lines "\^u2\^k") => "\^u2\^k"It you wish to use
fsetto make an alternate name for a function, consider usingdefaliasinstead. See Definition of defalias.
As explained in Variable Scoping, Emacs can optionally enable
lexical binding of variables. When lexical binding is enabled, any
named function that you create (e.g., with defun), as well as
any anonymous function that you create using the lambda macro
or the function special form or the #' syntax
(see Anonymous Functions), is automatically converted into a
closure.
A closure is a function that also carries a record of the lexical environment that existed when the function was defined. When it is invoked, any lexical variable references within its definition use the retained lexical environment. In all other respects, closures behave much like ordinary functions; in particular, they can be called in the same way as ordinary functions.
See Lexical Binding, for an example of using a closure.
Currently, an Emacs Lisp closure object is represented by a list
with the symbol closure as the first element, a list
representing the lexical environment as the second element, and the
argument list and body forms as the remaining elements:
;; lexical binding is enabled.
(lambda (x) (* x x))
=> (closure (t) (x) (* x x))
However, the fact that the internal structure of a closure is exposed to the rest of the Lisp world is considered an internal implementation detail. For this reason, we recommend against directly examining or altering the structure of closure objects.
When you need to modify a function defined in another library, or when you need
to modify a hook like foo-function, a process filter, or basically
any variable or object field which holds a function value, you can use the
appropriate setter function, such as fset or defun for named
functions, setq for hook variables, or set-process-filter for
process filters, but those are often too blunt, completely throwing away the
previous value.
The advice feature lets you add to the existing definition of a function, by advising the function. This is a cleaner method than redefining the whole function.
Emacs's advice system provides two sets of primitives for that: the core set,
for function values held in variables and object fields (with the corresponding
primitives being add-function and remove-function) and another
set layered on top of it for named functions (with the main primitives being
advice-add and advice-remove).
For example, in order to trace the calls to the process filter of a process proc, you could use:
(defun my-tracing-function (proc string)
(message "Proc %S received %S" proc string))
(add-function :before (process-filter proc) #'my-tracing-function)
This will cause the process's output to be passed to my-tracing-function
before being passed to the original process filter. my-tracing-function
receives the same arguments as the original function. When you're done with
it, you can revert to the untraced behavior with:
(remove-function (process-filter proc) #'my-tracing-function)
Similarly, if you want to trace the execution of the function named
display-buffer, you could use:
(defun his-tracing-function (orig-fun &rest args)
(message "display-buffer called with args %S" args)
(let ((res (apply orig-fun args)))
(message "display-buffer returned %S" res)
res))
(advice-add 'display-buffer :around #'his-tracing-function)
Here, his-tracing-function is called instead of the original function
and receives the original function (additionally to that function's arguments)
as argument, so it can call it if and when it needs to.
When you're tired of seeing this output, you can revert to the untraced
behavior with:
(advice-remove 'display-buffer #'his-tracing-function)
The arguments :before and :around used in the above examples
specify how the two functions are composed, since there are many different
ways to do it. The added function is also called a piece of advice.
This macro is the handy way to add the advice function to the function stored in place (see Generalized Variables).
where determines how function is composed with the existing function, e.g., whether function should be called before, or after the original function. See Advice combinators, for the list of available ways to compose the two functions.
When modifying a variable (whose name will usually end with
-function), you can choose whether function is used globally or only in the current buffer: if place is just a symbol, then function is added to the global value of place. Whereas if place is of the form(localsymbol), where symbol is an expression which returns the variable name, then function will only be added in the current buffer. Finally, if you want to modify a lexical variable, you will have to use(varvariable).Every function added with
add-functioncan be accompanied by an association list of properties props. Currently only two of those properties have a special meaning:
name- This gives a name to the advice, which
remove-functioncan use to identify which function to remove. Typically used when function is an anonymous function.
depth- This specifies how to order the advice, should several pieces of advice be present. By default, the depth is 0. A depth of 100 indicates that this piece of advice should be kept as deep as possible, whereas a depth of -100 indicates that it should stay as the outermost piece. When two pieces of advice specify the same depth, the most recently added one will be outermost.
For
:beforeadvice, being outermost means that this advice will be run first, before any other advice, whereas being innermost means that it will run right before the original function, with no other advice run between itself and the original function. Similarly, for:afteradvice innermost means that it will run right after the original function, with no other advice run in between, whereas outermost means that it will be run right at the end after all other advice. An innermost:overridepiece of advice will only override the original function and other pieces of advice will apply to it, whereas an outermost:overridepiece of advice will override not only the original function but all other advice applied to it as well.If function is not interactive, then the combined function will inherit the interactive spec, if any, of the original function. Else, the combined function will be interactive and will use the interactive spec of function. One exception: if the interactive spec of function is a function (rather than an expression or a string), then the interactive spec of the combined function will be a call to that function with as sole argument the interactive spec of the original function. To interpret the spec received as argument, use
advice-eval-interactive-spec.Note: The interactive spec of function will apply to the combined function and should hence obey the calling convention of the combined function rather than that of function. In many cases, it makes no difference since they are identical, but it does matter for
:around,:filter-args, andfilter-return, where function.
This macro removes function from the function stored in place. This only works if function was added to place using
add-function.function is compared with functions added to place using
equal, to try and make it work also with lambda expressions. It is additionally compared also with thenameproperty of the functions added to place, which can be more reliable than comparing lambda expressions usingequal.
Return non-
nilif advice is already in function-def. Like forremove-functionabove, instead of advice being the actual function, it can also be thenameof the piece of advice.
Call the function f for every piece of advice that was added to function-def. f is called with two arguments: the advice function and its properties.
Evaluate the interactive spec just like an interactive call to a function with such a spec would, and then return the corresponding list of arguments that was built. E.g.,
(advice-eval-interactive-spec "r\nP")will return a list of three elements, containing the boundaries of the region and the current prefix argument.
A common use of advice is for named functions and macros.
You could just use add-function as in:
(add-function :around (symbol-function 'fun) #'his-tracing-function)
But you should use advice-add and advice-remove for that
instead. This separate set of functions to manipulate pieces of advice applied
to named functions, offers the following extra features compared to
add-function: they know how to deal with macros and autoloaded
functions, they let describe-function preserve the original docstring as
well as document the added advice, and they let you add and remove advice
before a function is even defined.
advice-add can be useful for altering the behavior of existing calls
to an existing function without having to redefine the whole function.
However, it can be a source of bugs, since existing callers to the function may
assume the old behavior, and work incorrectly when the behavior is changed by
advice. Advice can also cause confusion in debugging, if the person doing the
debugging does not notice or remember that the function has been modified
by advice.
For these reasons, advice should be reserved for the cases where you cannot modify a function's behavior in any other way. If it is possible to do the same thing via a hook, that is preferable (see Hooks). If you simply want to change what a particular key does, it may be better to write a new command, and remap the old command's key bindings to the new one (see Remapping Commands). In particular, Emacs's own source files should not put advice on functions in Emacs. (There are currently a few exceptions to this convention, but we aim to correct them.)
Special forms (see Special Forms) cannot be advised, however macros can be advised, in much the same way as functions. Of course, this will not affect code that has already been macro-expanded, so you need to make sure the advice is installed before the macro is expanded.
It is possible to advise a primitive (see What Is a Function), but one should typically not do so, for two reasons. Firstly, some primitives are used by the advice mechanism, and advising them could cause an infinite recursion. Secondly, many primitives are called directly from C, and such calls ignore advice; hence, one ends up in a confusing situation where some calls (occurring from Lisp code) obey the advice and other calls (from C code) do not.
This macro defines a piece of advice and adds it to the function named symbol. The advice is an anonymous function if name is nil or a function named
symbol@name. Seeadvice-addfor explanation of other arguments.
Add the advice function to the named function symbol. where and props have the same meaning as for
add-function(see Core Advising Primitives).
Remove the advice function from the named function symbol. function can also be the
nameof a piece of advice.
Return non-
nilif the advice function is already in the named function symbol. function can also be thenameof a piece of advice.
Call function for every piece of advice that was added to the named function symbol. function is called with two arguments: the advice function and its properties.
Here are the different possible values for the where argument of
add-function and advice-add, specifying how the advice
function and the original function should be composed.
:before (lambda (&rest r) (apply function r) (apply oldfun r))
(add-function :before funvar function) is comparable for
single-function hooks to (add-hook 'hookvar function) for
normal hooks.
:after (lambda (&rest r) (prog1 (apply oldfun r) (apply function r)))
(add-function :after funvar function) is comparable for
single-function hooks to (add-hook 'hookvar function
'append) for normal hooks.
:overrideremove-function.
:around (lambda (&rest r) (apply function oldfun r))
:before-whilenil. Both functions receive the
same arguments, and the return value of the composition is the return value of
the old function. More specifically, the composition of the two functions
behaves like:
(lambda (&rest r) (and (apply function r) (apply oldfun r)))
(add-function :before-while funvar function) is comparable
for single-function hooks to (add-hook 'hookvar function)
when hookvar is run via run-hook-with-args-until-failure.
:before-untilnil. More specifically, the composition of the
two functions behaves like:
(lambda (&rest r) (or (apply function r) (apply oldfun r)))
(add-function :before-until funvar function) is comparable
for single-function hooks to (add-hook 'hookvar function)
when hookvar is run via run-hook-with-args-until-success.
:after-whilenil. Both functions receive the same arguments, and the
return value of the composition is the return value of function.
More specifically, the composition of the two functions behaves like:
(lambda (&rest r) (and (apply oldfun r) (apply function r)))
(add-function :after-while funvar function) is comparable
for single-function hooks to (add-hook 'hookvar function
'append) when hookvar is run via
run-hook-with-args-until-failure.
:after-untilnil. More specifically, the composition of the two functions
behaves like:
(lambda (&rest r) (or (apply oldfun r) (apply function r)))
(add-function :after-until funvar function) is comparable
for single-function hooks to (add-hook 'hookvar function
'append) when hookvar is run via
run-hook-with-args-until-success.
:filter-args (lambda (&rest r) (apply oldfun (funcall function r)))
:filter-return (lambda (&rest r) (funcall function (apply oldfun r)))
A lot of code uses the old defadvice mechanism, which is largely made
obsolete by the new advice-add, whose implementation and semantics is
significantly simpler.
An old piece of advice such as:
(defadvice previous-line (before next-line-at-end
(&optional arg try-vscroll))
"Insert an empty line when moving up from the top line."
(if (and next-line-add-newlines (= arg 1)
(save-excursion (beginning-of-line) (bobp)))
(progn
(beginning-of-line)
(newline))))
could be translated in the new advice mechanism into a plain function:
(defun previous-line--next-line-at-end (&optional arg try-vscroll)
"Insert an empty line when moving up from the top line."
(if (and next-line-add-newlines (= arg 1)
(save-excursion (beginning-of-line) (bobp)))
(progn
(beginning-of-line)
(newline))))
Obviously, this does not actually modify previous-line. For that the
old advice needed:
(ad-activate 'previous-line)
whereas the new advice mechanism needs:
(advice-add 'previous-line :before #'previous-line--next-line-at-end)
Note that ad-activate had a global effect: it activated all pieces of
advice enabled for that specified function. If you wanted to only activate or
deactivate a particular piece, you needed to enable or disable
it with ad-enable-advice and ad-disable-advice.
The new mechanism does away with this distinction.
Around advice such as:
(defadvice foo (around foo-around)
"Ignore case in `foo'."
(let ((case-fold-search t))
ad-do-it))
(ad-activate 'foo)
could translate into:
(defun foo--foo-around (orig-fun &rest args)
"Ignore case in `foo'."
(let ((case-fold-search t))
(apply orig-fun args)))
(advice-add 'foo :around #'foo--foo-around)
Regarding the advice's class, note that the new :before is not
quite equivalent to the old before, because in the old advice you could
modify the function's arguments (e.g., with ad-set-arg), and that would
affect the argument values seen by the original function, whereas in the new
:before, modifying an argument via setq in the advice has no
effect on the arguments seen by the original function.
When porting before advice which relied on this behavior, you'll need
to turn it into new :around or :filter-args advice instead.
Similarly old after advice could modify the returned value by
changing ad-return-value, whereas new :after advice cannot, so
when porting such old after advice, you'll need to turn it into new
:around or :filter-return advice instead.
You can mark a named function as obsolete, meaning that it may be removed at some point in the future. This causes Emacs to warn that the function is obsolete whenever it byte-compiles code containing that function, and whenever it displays the documentation for that function. In all other respects, an obsolete function behaves like any other function.
The easiest way to mark a function as obsolete is to put a
(declare (obsolete ...)) form in the function's
defun definition. See Declare Form. Alternatively, you can
use the make-obsolete function, described below.
A macro (see Macros) can also be marked obsolete with
make-obsolete; this has the same effects as for a function. An
alias for a function or macro can also be marked as obsolete; this
makes the alias itself obsolete, not the function or macro which it
resolves to.
This function marks obsolete-name as obsolete. obsolete-name should be a symbol naming a function or macro, or an alias for a function or macro.
If current-name is a symbol, the warning message says to use current-name instead of obsolete-name. current-name does not need to be an alias for obsolete-name; it can be a different function with similar functionality. current-name can also be a string, which serves as the warning message. The message should begin in lower case, and end with a period. It can also be
nil, in which case the warning message provides no additional details.If provided, when should be a string indicating when the function was first made obsolete—for example, a date or a release number.
This convenience macro marks the function obsolete-name obsolete and also defines it as an alias for the function current-name. It is equivalent to the following:
(defalias obsolete-name current-name doc) (make-obsolete obsolete-name current-name when)
In addition, you can mark a certain a particular calling convention for a function as obsolete:
This function specifies the argument list signature as the correct way to call function. This causes the Emacs byte compiler to issue a warning whenever it comes across an Emacs Lisp program that calls function any other way (however, it will still allow the code to be byte compiled). when should be a string indicating when the variable was first made obsolete (usually a version number string).
For instance, in old versions of Emacs the
sit-forfunction accepted three arguments, like this(sit-for seconds milliseconds nodisp)However, calling
sit-forthis way is considered obsolete (see Waiting). The old calling convention is deprecated like this:(set-advertised-calling-convention 'sit-for '(seconds &optional nodisp) "22.1")
An inline function is a function that works just like an
ordinary function, except for one thing: when you byte-compile a call
to the function (see Byte Compilation), the function's definition
is expanded into the caller. To define an inline function, use
defsubst instead of defun.
This macro defines an inline function. Its syntax is exactly the same as
defun(see Defining Functions).
Making a function inline often makes its function calls run faster. But it also has disadvantages. For one thing, it reduces flexibility; if you change the definition of the function, calls already inlined still use the old definition until you recompile them.
Another disadvantage is that making a large function inline can increase the size of compiled code both in files and in memory. Since the speed advantage of inline functions is greatest for small functions, you generally should not make large functions inline.
Also, inline functions do not behave well with respect to debugging,
tracing, and advising (see Advising Functions). Since ease of
debugging and the flexibility of redefining functions are important
features of Emacs, you should not make a function inline, even if it's
small, unless its speed is really crucial, and you've timed the code
to verify that using defun actually has performance problems.
After an inline function is defined, its inline expansion can be performed later on in the same file, just like macros.
It's possible to use defsubst to define a macro to expand
into the same code that an inline function would execute
(see Macros). But the macro would be limited to direct use in
expressions—a macro cannot be called with apply,
mapcar and so on. Also, it takes some work to convert an
ordinary function into a macro. To convert it into an inline function
is easy; just replace defun with defsubst. Since each
argument of an inline function is evaluated exactly once, you needn't
worry about how many times the body uses the arguments, as you do for
macros.
As an alternative to defsubst, you can use
define-inline to define functions via their exhaustive compiler
macro. See define-inline.
declare Form
declare is a special macro which can be used to add meta
properties to a function or macro: for example, marking it as
obsolete, or giving its forms a special <TAB> indentation
convention in Emacs Lisp mode.
This macro ignores its arguments and evaluates to
nil; it has no run-time effect. However, when adeclareform occurs in the declare argument of adefunordefsubstfunction definition (see Defining Functions) or adefmacromacro definition (see Defining Macros), it appends the properties specified by specs to the function or macro. This work is specially performed bydefun,defsubst, anddefmacro.Each element in specs should have the form
(property args...), which should not be quoted. These have the following effects:
(advertised-calling-conventionsignature when)- This acts like a call to
set-advertised-calling-convention(see Obsolete Functions); signature specifies the correct argument list for calling the function or macro, and when should be a string indicating when the old argument list was first made obsolete.
(debugedebug-form-spec)- This is valid for macros only. When stepping through the macro with Edebug, use edebug-form-spec. See Instrumenting Macro Calls.
(doc-stringn)- This is used when defining a function or macro which itself will be used to define entities like functions, macros, or variables. It indicates that the nth argument, if any, should be considered as a documentation string.
(indentindent-spec)- Indent calls to this function or macro according to indent-spec. This is typically used for macros, though it works for functions too. See Indenting Macros.
(interactive-onlyvalue)- Set the function's
interactive-onlyproperty to value. See The interactive-only property.
(obsoletecurrent-name when)- Mark the function or macro as obsolete, similar to a call to
make-obsolete(see Obsolete Functions). current-name should be a symbol (in which case the warning message says to use that instead), a string (specifying the warning message), ornil(in which case the warning message gives no extra details). when should be a string indicating when the function or macro was first made obsolete.
(compiler-macroexpander)- This can only be used for functions, and tells the compiler to use expander as an optimization function. When encountering a call to the function, of the form
(function args...), the macro expander will call expander with that form as well as with args..., and expander can either return a new expression to use instead of the function call, or it can return just the form unchanged, to indicate that the function call should be left alone. expander can be a symbol, or it can be a form(lambda (arg)body)in which case arg will hold the original function call expression, and the (unevaluated) arguments to the function can be accessed using the function's formal arguments.
(gv-expanderexpander)- Declare expander to be the function to handle calls to the macro (or function) as a generalized variable, similarly to
gv-define-expander. expander can be a symbol or it can be of the form(lambda (arg)body)in which case that function will additionally have access to the macro (or function)'s arguments.
(gv-settersetter)- Declare setter to be the function to handle calls to the macro (or function) as a generalized variable. setter can be a symbol in which case it will be passed to
gv-define-simple-setter, or it can be of the form(lambda (arg)body)in which case that function will additionally have access to the macro (or function)'s arguments and it will passed togv-define-setter.
Byte-compiling a file often produces warnings about functions that the compiler doesn't know about (see Compiler Errors). Sometimes this indicates a real problem, but usually the functions in question are defined in other files which would be loaded if that code is run. For example, byte-compiling fortran.el used to warn:
In end of data:
fortran.el:2152:1:Warning: the function ‘gud-find-c-expr’ is not
known to be defined.
In fact, gud-find-c-expr is only used in the function that
Fortran mode uses for the local value of
gud-find-expr-function, which is a callback from GUD; if it is
called, the GUD functions will be loaded. When you know that such a
warning does not indicate a real problem, it is good to suppress the
warning. That makes new warnings which might mean real problems more
visible. You do that with declare-function.
All you need to do is add a declare-function statement before the
first use of the function in question:
(declare-function gud-find-c-expr "gud.el" nil)
This says that gud-find-c-expr is defined in gud.el (the
`.el' can be omitted). The compiler takes for granted that that file
really defines the function, and does not check.
The optional third argument specifies the argument list of
gud-find-c-expr. In this case, it takes no arguments
(nil is different from not specifying a value). In other
cases, this might be something like (file &optional overwrite).
You don't have to specify the argument list, but if you do the
byte compiler can check that the calls match the declaration.
Tell the byte compiler to assume that function is defined, with arguments arglist, and that the definition should come from the file file. fileonly non-
nilmeans only check that file exists, not that it actually defines function.
To verify that these functions really are declared where
declare-function says they are, use check-declare-file
to check all declare-function calls in one source file, or use
check-declare-directory check all the files in and under a
certain directory.
These commands find the file that ought to contain a function's
definition using locate-library; if that finds no file, they
expand the definition file name relative to the directory of the file
that contains the declare-function call.
You can also say that a function is a primitive by specifying a file name ending in `.c' or `.m'. This is useful only when you call a primitive that is defined only on certain systems. Most primitives are always defined, so they will never give you a warning.
Sometimes a file will optionally use functions from an external package.
If you prefix the filename in the declare-function statement with
`ext:', then it will be checked if it is found, otherwise skipped
without error.
There are some function definitions that `check-declare' does not
understand (e.g., defstruct and some other macros). In such cases,
you can pass a non-nil fileonly argument to
declare-function, meaning to only check that the file exists, not
that it actually defines the function. Note that to do this without
having to specify an argument list, you should set the arglist
argument to t (because nil means an empty argument list, as
opposed to an unspecified one).
Some major modes, such as SES, call functions that are stored in user files. (see Top, for more information on SES.) User files sometimes have poor pedigrees—you can get a spreadsheet from someone you've just met, or you can get one through email from someone you've never met. So it is risky to call a function whose source code is stored in a user file until you have determined that it is safe.
Returns
nilif form is a safe Lisp expression, or returns a list that describes why it might be unsafe. The argument unsafep-vars is a list of symbols known to have temporary bindings at this point; it is mainly used for internal recursive calls. The current buffer is an implicit argument, which provides a list of buffer-local bindings.
Being quick and simple, unsafep does a very light analysis and
rejects many Lisp expressions that are actually safe. There are no
known cases where unsafep returns nil for an unsafe
expression. However, a safe Lisp expression can return a string
with a display property, containing an associated Lisp
expression to be executed after the string is inserted into a buffer.
This associated expression can be a virus. In order to be safe, you
must delete properties from all strings calculated by user code before
inserting them into buffers.
Here is a table of several functions that do things related to function calling and function definitions. They are documented elsewhere, but we provide cross references here.
applyautoloadcall-interactivelycalled-interactively-pcommandpdocumentationevalfuncallfunctionignoreindirect-functioninteractiveinteractive-pmapatomsmapcarmap-char-tablemapconcatundefinedMacros enable you to define new control constructs and other language features. A macro is defined much like a function, but instead of telling how to compute a value, it tells how to compute another Lisp expression which will in turn compute the value. We call this expression the expansion of the macro.
Macros can do this because they operate on the unevaluated expressions for the arguments, not on the argument values as functions do. They can therefore construct an expansion containing these argument expressions or parts of them.
If you are using a macro to do something an ordinary function could do, just for the sake of speed, consider using an inline function instead. See Inline Functions.
Suppose we would like to define a Lisp construct to increment a
variable value, much like the ++ operator in C. We would like to
write (inc x) and have the effect of (setq x (1+ x)).
Here's a macro definition that does the job:
(defmacro inc (var)
(list 'setq var (list '1+ var)))
When this is called with (inc x), the argument var is the
symbol x—not the value of x, as it would
be in a function. The body of the macro uses this to construct the
expansion, which is (setq x (1+ x)). Once the macro definition
returns this expansion, Lisp proceeds to evaluate it, thus incrementing
x.
This predicate tests whether its argument is a macro, and returns
tif so,nilotherwise.
A macro call looks just like a function call in that it is a list which starts with the name of the macro. The rest of the elements of the list are the arguments of the macro.
Evaluation of the macro call begins like evaluation of a function call except for one crucial difference: the macro arguments are the actual expressions appearing in the macro call. They are not evaluated before they are given to the macro definition. By contrast, the arguments of a function are results of evaluating the elements of the function call list.
Having obtained the arguments, Lisp invokes the macro definition just
as a function is invoked. The argument variables of the macro are bound
to the argument values from the macro call, or to a list of them in the
case of a &rest argument. And the macro body executes and
returns its value just as a function body does.
The second crucial difference between macros and functions is that the value returned by the macro body is an alternate Lisp expression, also known as the expansion of the macro. The Lisp interpreter proceeds to evaluate the expansion as soon as it comes back from the macro.
Since the expansion is evaluated in the normal manner, it may contain calls to other macros. It may even be a call to the same macro, though this is unusual.
Note that Emacs tries to expand macros when loading an uncompiled Lisp file. This is not always possible, but if it is, it speeds up subsequent execution. See How Programs Do Loading.
You can see the expansion of a given macro call by calling
macroexpand.
This function expands form, if it is a macro call. If the result is another macro call, it is expanded in turn, until something which is not a macro call results. That is the value returned by
macroexpand. If form is not a macro call to begin with, it is returned as given.Note that
macroexpanddoes not look at the subexpressions of form (although some macro definitions may do so). Even if they are macro calls themselves,macroexpanddoes not expand them.The function
macroexpanddoes not expand calls to inline functions. Normally there is no need for that, since a call to an inline function is no harder to understand than a call to an ordinary function.If environment is provided, it specifies an alist of macro definitions that shadow the currently defined macros. Byte compilation uses this feature.
(defmacro inc (var) (list 'setq var (list '1+ var))) (macroexpand '(inc r)) => (setq r (1+ r)) (defmacro inc2 (var1 var2) (list 'progn (list 'inc var1) (list 'inc var2))) (macroexpand '(inc2 r s)) => (progn (inc r) (inc s)) ;incnot expanded here.
macroexpand-allexpands macros likemacroexpand, but will look for and expand all macros in form, not just at the top-level. If no macros are expanded, the return value iseqto form.Repeating the example used for
macroexpandabove withmacroexpand-all, we see thatmacroexpand-alldoes expand the embedded calls toinc:(macroexpand-all '(inc2 r s)) => (progn (setq r (1+ r)) (setq s (1+ s)))
This function expands macros like
macroexpand, but it only performs one step of the expansion: if the result is another macro call,macroexpand-1will not expand it.
You might ask why we take the trouble to compute an expansion for a macro and then evaluate the expansion. Why not have the macro body produce the desired results directly? The reason has to do with compilation.
When a macro call appears in a Lisp program being compiled, the Lisp compiler calls the macro definition just as the interpreter would, and receives an expansion. But instead of evaluating this expansion, it compiles the expansion as if it had appeared directly in the program. As a result, the compiled code produces the value and side effects intended for the macro, but executes at full compiled speed. This would not work if the macro body computed the value and side effects itself—they would be computed at compile time, which is not useful.
In order for compilation of macro calls to work, the macros must
already be defined in Lisp when the calls to them are compiled. The
compiler has a special feature to help you do this: if a file being
compiled contains a defmacro form, the macro is defined
temporarily for the rest of the compilation of that file.
Byte-compiling a file also executes any require calls at
top-level in the file, so you can ensure that necessary macro
definitions are available during compilation by requiring the files
that define them (see Named Features). To avoid loading the macro
definition files when someone runs the compiled program, write
eval-when-compile around the require calls (see Eval During Compile).
A Lisp macro object is a list whose car is macro, and
whose cdr is a function. Expansion of the macro works
by applying the function (with apply) to the list of
unevaluated arguments from the macro call.
It is possible to use an anonymous Lisp macro just like an anonymous
function, but this is never done, because it does not make sense to
pass an anonymous macro to functionals such as mapcar. In
practice, all Lisp macros have names, and they are almost always
defined with the defmacro macro.
defmacrodefines the symbol name (which should not be quoted) as a macro that looks like this:(macro lambda args . body)(Note that the cdr of this list is a lambda expression.) This macro object is stored in the function cell of name. The meaning of args is the same as in a function, and the keywords
&restand&optionalmay be used (see Argument List). Neither name nor args should be quoted. The return value ofdefmacrois undefined.doc, if present, should be a string specifying the macro's documentation string. declare, if present, should be a
declareform specifying metadata for the macro (see Declare Form). Note that macros cannot have interactive declarations, since they cannot be called interactively.
Macros often need to construct large list structures from a mixture of constants and nonconstant parts. To make this easier, use the ``' syntax (see Backquote). For example:
(defmacro t-becomes-nil (variable)
`(if (eq ,variable t)
(setq ,variable nil)))
(t-becomes-nil foo)
== (if (eq foo t) (setq foo nil))
The body of a macro definition can include a declare form,
which specifies additional properties about the macro. See Declare Form.
Macro expansion can have counterintuitive consequences. This section describes some important consequences that can lead to trouble, and rules to follow to avoid trouble.
The most common problem in writing macros is doing some of the real work prematurely—while expanding the macro, rather than in the expansion itself. For instance, one real package had this macro definition:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
(set-buffer-multibyte arg)))
With this erroneous macro definition, the program worked fine when
interpreted but failed when compiled. This macro definition called
set-buffer-multibyte during compilation, which was wrong, and
then did nothing when the compiled package was run. The definition
that the programmer really wanted was this:
(defmacro my-set-buffer-multibyte (arg)
(if (fboundp 'set-buffer-multibyte)
`(set-buffer-multibyte ,arg)))
This macro expands, if appropriate, into a call to
set-buffer-multibyte that will be executed when the compiled
program is actually run.
When defining a macro you must pay attention to the number of times the arguments will be evaluated when the expansion is executed. The following macro (used to facilitate iteration) illustrates the problem. This macro allows us to write a for-loop construct.
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(list 'let (list (list var init))
(cons 'while
(cons (list '<= var final)
(append body (list (list 'inc var)))))))
(for i from 1 to 3 do
(setq square (* i i))
(princ (format "\n%d %d" i square)))
==>
(let ((i 1))
(while (<= i 3)
(setq square (* i i))
(princ (format "\n%d %d" i square))
(inc i)))
-|1 1
-|2 4
-|3 9
=> nil
The arguments from, to, and do in this macro are
syntactic sugar; they are entirely ignored. The idea is that you
will write noise words (such as from, to, and do)
in those positions in the macro call.
Here's an equivalent definition simplified through use of backquote:
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
`(let ((,var ,init))
(while (<= ,var ,final)
,@body
(inc ,var))))
Both forms of this definition (with backquote and without) suffer from
the defect that final is evaluated on every iteration. If
final is a constant, this is not a problem. If it is a more
complex form, say (long-complex-calculation x), this can slow
down the execution significantly. If final has side effects,
executing it more than once is probably incorrect.
A well-designed macro definition takes steps to avoid this problem by
producing an expansion that evaluates the argument expressions exactly
once unless repeated evaluation is part of the intended purpose of the
macro. Here is a correct expansion for the for macro:
(let ((i 1)
(max 3))
(while (<= i max)
(setq square (* i i))
(princ (format "%d %d" i square))
(inc i)))
Here is a macro definition that creates this expansion:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
Unfortunately, this fix introduces another problem, described in the following section.
In the previous section, the definition of for was fixed as
follows to make the expansion evaluate the macro arguments the proper
number of times:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
`(let ((,var ,init)
(max ,final))
(while (<= ,var max)
,@body
(inc ,var))))
The new definition of for has a new problem: it introduces a
local variable named max which the user does not expect. This
causes trouble in examples such as the following:
(let ((max 0))
(for x from 0 to 10 do
(let ((this (frob x)))
(if (< max this)
(setq max this)))))
The references to max inside the body of the for, which
are supposed to refer to the user's binding of max, really access
the binding made by for.
The way to correct this is to use an uninterned symbol instead of
max (see Creating Symbols). The uninterned symbol can be
bound and referred to just like any other symbol, but since it is
created by for, we know that it cannot already appear in the
user's program. Since it is not interned, there is no way the user can
put it into the program later. It will never appear anywhere except
where put by for. Here is a definition of for that works
this way:
(defmacro for (var from init to final do &rest body)
"Execute a simple for loop: (for i from 1 to 10 do (print i))."
(let ((tempvar (make-symbol "max")))
`(let ((,var ,init)
(,tempvar ,final))
(while (<= ,var ,tempvar)
,@body
(inc ,var)))))
This creates an uninterned symbol named max and puts it in the
expansion instead of the usual interned symbol max that appears
in expressions ordinarily.
Another problem can happen if the macro definition itself
evaluates any of the macro argument expressions, such as by calling
eval (see Eval). If the argument is supposed to refer to the
user's variables, you may have trouble if the user happens to use a
variable with the same name as one of the macro arguments. Inside the
macro body, the macro argument binding is the most local binding of this
variable, so any references inside the form being evaluated do refer to
it. Here is an example:
(defmacro foo (a)
(list 'setq (eval a) t))
(setq x 'b)
(foo x) ==> (setq b t)
=> t ; and b has been set.
;; but
(setq a 'c)
(foo a) ==> (setq a t)
=> t ; but this set a, not c.
It makes a difference whether the user's variable is named a or
x, because a conflicts with the macro argument variable
a.
Another problem with calling eval in a macro definition is that
it probably won't do what you intend in a compiled program. The
byte compiler runs macro definitions while compiling the program, when
the program's own computations (which you might have wished to access
with eval) don't occur and its local variable bindings don't
exist.
To avoid these problems, don't evaluate an argument expression while computing the macro expansion. Instead, substitute the expression into the macro expansion, so that its value will be computed as part of executing the expansion. This is how the other examples in this chapter work.
Occasionally problems result from the fact that a macro call is expanded each time it is evaluated in an interpreted function, but is expanded only once (during compilation) for a compiled function. If the macro definition has side effects, they will work differently depending on how many times the macro is expanded.
Therefore, you should avoid side effects in computation of the macro expansion, unless you really know what you are doing.
One special kind of side effect can't be avoided: constructing Lisp objects. Almost all macro expansions include constructed lists; that is the whole point of most macros. This is usually safe; there is just one case where you must be careful: when the object you construct is part of a quoted constant in the macro expansion.
If the macro is expanded just once, in compilation, then the object is constructed just once, during compilation. But in interpreted execution, the macro is expanded each time the macro call runs, and this means a new object is constructed each time.
In most clean Lisp code, this difference won't matter. It can matter only if you perform side-effects on the objects constructed by the macro definition. Thus, to avoid trouble, avoid side effects on objects constructed by macro definitions. Here is an example of how such side effects can get you into trouble:
(defmacro empty-object ()
(list 'quote (cons nil nil)))
(defun initialize (condition)
(let ((object (empty-object)))
(if condition
(setcar object condition))
object))
If initialize is interpreted, a new list (nil) is
constructed each time initialize is called. Thus, no side effect
survives between calls. If initialize is compiled, then the
macro empty-object is expanded during compilation, producing a
single constant (nil) that is reused and altered each time
initialize is called.
One way to avoid pathological cases like this is to think of
empty-object as a funny kind of constant, not as a memory
allocation construct. You wouldn't use setcar on a constant such
as '(nil), so naturally you won't use it on (empty-object)
either.
Within a macro definition, you can use the declare form
(see Defining Macros) to specify how <TAB> should indent
calls to the macro. An indentation specification is written like this:
(declare (indent indent-spec))
This results in the lisp-indent-function property being set on
the macro name.
Here are the possibilities for indent-spec:
nildefunlisp-body-indent
more columns than the open-parenthesis starting the containing
expression. If the argument is distinguished and is either the first
or second argument, it is indented twice that many extra columns.
If the argument is distinguished and not the first or second argument,
the line uses the standard pattern.
parse-partial-sexp (a Lisp primitive for
indentation and nesting computation) when it parses up to the
beginning of this line.
It should return either a number, which is the number of columns of indentation for that line, or a list whose car is such a number. The difference between returning a number and returning a list is that a number says that all following lines at the same nesting level should be indented just like this one; a list says that following lines might call for different indentations. This makes a difference when the indentation is being computed by C-M-q; if the value is a number, C-M-q need not recalculate indentation for the following lines until the end of the list.
Users of Emacs can customize variables and faces without writing Lisp code, by using the Customize interface. See Easy Customization. This chapter describes how to define customization items that users can interact with through the Customize interface.
Customization items include customizable variables, which are
defined with the
defcustom macro;
customizable faces, which are defined with defface (described
separately in Defining Faces); and customization groups,
defined with
defgroup,
which act as containers for groups of related customization items.
The customization declarations that we will describe in the next few
sections—defcustom, defgroup, etc.—all accept
keyword arguments (see Constant Variables) for specifying various
information. This section describes keywords that apply to all types
of customization declarations.
All of these keywords, except :tag, can be used more than once
in a given item. Each use of the keyword has an independent effect.
The keyword :tag is an exception because any given item can only
display one name.
:tag label
:group group
When you use :group in a defgroup, it makes the new
group a subgroup of group.
If you use this keyword more than once, you can put a single item into
more than one group. Displaying any of those groups will show this
item. Please don't overdo this, since the result would be annoying.
:link link-data
There are several alternatives you can use for link-data:
(custom-manual info-node)
"(emacs)Top". The link appears as
`[Manual]' in the customization buffer and enters the built-in
Info reader on info-node.
(info-link info-node)
custom-manual except that the link appears
in the customization buffer with the Info node name.
(url-link url)
browse-url-browser-function.
(emacs-commentary-link library)
(emacs-library-link library)
(file-link file)
find-file when the user invokes this link.
(function-link function)
describe-function when the user invokes this link.
(variable-link variable)
describe-variable when the user invokes this link.
(custom-group-link group)
You can specify the text to use in the customization buffer by adding
:tag name after the first element of the link-data;
for example, (info-link :tag "foo" "(emacs)Top") makes a link to
the Emacs manual which appears in the buffer as `foo'.
You can use this keyword more than once, to add multiple links.
:load file
load, and only if
the file is not already loaded.
:require feature
(require 'feature) when your saved customizations
set the value of this item. feature should be a symbol.
The most common reason to use :require is when a variable enables
a feature such as a minor mode, and just setting the variable won't have
any effect unless the code which implements the mode is loaded.
:version version
:package-version '(package . version)
:version.
package should be the official name of the package, as a symbol
(e.g., MH-E). version should be a string. If the
package package is released as part of Emacs, package and
version should appear in the value of
customize-package-emacs-version-alist.
Packages distributed as part of Emacs that use the
:package-version keyword must also update the
customize-package-emacs-version-alist variable.
This alist provides a mapping for the versions of Emacs that are associated with versions of a package listed in the
:package-versionkeyword. Its elements are:(package (pversion . eversion)...)For each package, which is a symbol, there are one or more elements that contain a package version pversion with an associated Emacs version eversion. These versions are strings. For example, the MH-E package updates this alist with the following:
(add-to-list 'customize-package-emacs-version-alist '(MH-E ("6.0" . "22.1") ("6.1" . "22.1") ("7.0" . "22.1") ("7.1" . "22.1") ("7.2" . "22.1") ("7.3" . "22.1") ("7.4" . "22.1") ("8.0" . "22.1")))The value of package needs to be unique and it needs to match the package value appearing in the
:package-versionkeyword. Since the user might see the value in an error message, a good choice is the official name of the package, such as MH-E or Gnus.
Each Emacs Lisp package should have one main customization group which contains all the options, faces and other groups in the package. If the package has a small number of options and faces, use just one group and put everything in it. When there are more than twenty or so options and faces, then you should structure them into subgroups, and put the subgroups under the package's main customization group. It is OK to put some of the options and faces in the package's main group alongside the subgroups.
The package's main or only group should be a member of one or more of
the standard customization groups. (To display the full list of them,
use M-x customize.) Choose one or more of them (but not too
many), and add your group to each of them using the :group
keyword.
The way to declare new customization groups is with defgroup.
Declare group as a customization group containing members. Do not quote the symbol group. The argument doc specifies the documentation string for the group.
The argument members is a list specifying an initial set of customization items to be members of the group. However, most often members is
nil, and you specify the group's members by using the:groupkeyword when defining those members.If you want to specify group members through members, each element should have the form
(name widget). Here name is a symbol, and widget is a widget type for editing that symbol. Useful widgets arecustom-variablefor a variable,custom-facefor a face, andcustom-groupfor a group.When you introduce a new group into Emacs, use the
:versionkeyword in thedefgroup; then you need not use it for the individual members of the group.In addition to the common keywords (see Common Keywords), you can also use this keyword in
defgroup:
If this variable is non-
nil, the prefixes specified by a group's:prefixkeyword are omitted from tag names, whenever the user customizes the group.The default value is
nil, i.e., the prefix-discarding feature is disabled. This is because discarding prefixes often leads to confusing names for options and faces.
Customizable variables, also called user options, are
global Lisp variables whose values can be set through the Customize
interface. Unlike other global variables, which are defined with
defvar (see Defining Variables), customizable variables are
defined using the defcustom macro. In addition to calling
defvar as a subroutine, defcustom states how the
variable should be displayed in the Customize interface, the values it
is allowed to take, etc.
This macro declares option as a user option (i.e., a customizable variable). You should not quote option.
The argument standard is an expression that specifies the standard value for option. Evaluating the
defcustomform evaluates standard, but does not necessarily bind the option to that value. If option already has a default value, it is left unchanged. If the user has already saved a customization for option, the user's customized value is installed as the default value. Otherwise, the result of evaluating standard is installed as the default value.Like
defvar, this macro marksoptionas a special variable, meaning that it should always be dynamically bound. If option is already lexically bound, that lexical binding remains in effect until the binding construct exits. See Variable Scoping.The expression standard can be evaluated at various other times, too—whenever the customization facility needs to know option's standard value. So be sure to use an expression which is harmless to evaluate at any time.
The argument doc specifies the documentation string for the variable.
If a
defcustomdoes not specify any:group, the last group defined withdefgroupin the same file will be used. This way, mostdefcustomdo not need an explicit:group.When you evaluate a
defcustomform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunarranges to set the variable unconditionally, without testing whether its value is void. (The same feature applies todefvar, see Defining Variables.) Usingeval-defunon a defcustom that is already defined calls the:setfunction (see below), if there is one.If you put a
defcustomin a pre-loaded Emacs Lisp file (see Building Emacs), the standard value installed at dump time might be incorrect, e.g., because another variable that it depends on has not been assigned the right value yet. In that case, usecustom-reevaluate-setting, described below, to re-evaluate the standard value after Emacs starts up.
In addition to the keywords listed in Common Keywords, this macro accepts the following keywords:
:type type
defcustom should specify
a value for this keyword.
:options value-list
This is meaningful only for certain types, currently including
hook, plist and alist. See the definition of the
individual types for a description of how to use :options.
:set setfunction
set-default.
If you specify this keyword, the variable's documentation string
should describe how to do the same job in hand-written Lisp code.
:get getfunction
default-value.
You have to really understand the workings of Custom to use
:get correctly. It is meant for values that are treated in
Custom as variables but are not actually stored in Lisp variables. It
is almost surely a mistake to specify getfunction for a value
that really is stored in a Lisp variable.
:initialize function
defcustom is evaluated. It should take two arguments,
the option name (a symbol) and the value. Here are some predefined
functions meant for use in this way:
custom-initialize-set:set function to initialize the variable, but
do not reinitialize it if it is already non-void.
custom-initialize-defaultcustom-initialize-set, but use the function
set-default to set the variable, instead of the variable's
:set function. This is the usual choice for a variable whose
:set function enables or disables a minor mode; with this choice,
defining the variable will not call the minor mode function, but
customizing the variable will do so.
custom-initialize-reset:set function to initialize the variable. If
the variable is already non-void, reset it by calling the :set
function using the current value (returned by the :get method).
This is the default :initialize function.
custom-initialize-changed:set function to initialize the variable, if it is
already set or has been customized; otherwise, just use
set-default.
custom-initialize-safe-setcustom-initialize-safe-defaultcustom-initialize-set
(custom-initialize-default, respectively), but catch errors.
If an error occurs during initialization, they set the variable to
nil using set-default, and signal no error.
These functions are meant for options defined in pre-loaded files,
where the standard expression may signal an error because some
required variable or function is not yet defined. The value normally
gets updated in startup.el, ignoring the value computed by
defcustom. After startup, if one unsets the value and
reevaluates the defcustom, the standard expression can be
evaluated without error.
:risky value
risky-local-variable property to
value (see File Local Variables).
:safe function
safe-local-variable property to
function (see File Local Variables).
:set-after variables
:set-after if setting this variable won't work properly unless
those other variables already have their intended values.
It is useful to specify the :require keyword for an option
that turns on a certain feature. This causes Emacs to load the
feature, if it is not already loaded, whenever the option is set.
See Common Keywords. Here is an example, from the library
saveplace.el:
(defcustom save-place nil
"Non-nil means automatically save place in each file..."
:type 'boolean
:require 'saveplace
:group 'save-place)
If a customization item has a type such as hook or
alist, which supports :options, you can add additional
values to the list from outside the defcustom declaration by
calling custom-add-frequent-value. For example, if you define a
function my-lisp-mode-initialization intended to be called from
emacs-lisp-mode-hook, you might want to add that to the list of
reasonable values for emacs-lisp-mode-hook, but not by editing
its definition. You can do it thus:
(custom-add-frequent-value 'emacs-lisp-mode-hook
'my-lisp-mode-initialization)
For the customization option symbol, add value to the list of reasonable values.
The precise effect of adding a value depends on the customization type of symbol.
Internally, defcustom uses the symbol property
standard-value to record the expression for the standard value,
saved-value to record the value saved by the user with the
customization buffer, and customized-value to record the value
set by the user with the customization buffer, but not saved.
See Symbol Properties. These properties are lists, the car of
which is an expression that evaluates to the value.
This function re-evaluates the standard value of symbol, which should be a user option declared via
defcustom. If the variable was customized, this function re-evaluates the saved value instead. Then it sets the user option to that value (using the option's:setproperty if that is defined).This is useful for customizable options that are defined before their value could be computed correctly. For example, during startup Emacs calls this function for some user options that were defined in pre-loaded Emacs Lisp files, but whose initial values depend on information available only at run-time.
This function returns non-
nilif arg is a customizable variable. A customizable variable is either a variable that has astandard-valueorcustom-autoloadproperty (usually meaning it was declared withdefcustom), or an alias for another customizable variable.
When you define a user option with defcustom, you must specify
its customization type. That is a Lisp object which describes (1)
which values are legitimate and (2) how to display the value in the
customization buffer for editing.
You specify the customization type in defcustom with the
:type keyword. The argument of :type is evaluated, but
only once when the defcustom is executed, so it isn't useful
for the value to vary. Normally we use a quoted constant. For
example:
(defcustom diff-command "diff"
"The command to use to run diff."
:type '(string)
:group 'diff)
In general, a customization type is a list whose first element is a symbol, one of the customization type names defined in the following sections. After this symbol come a number of arguments, depending on the symbol. Between the type symbol and its arguments, you can optionally write keyword-value pairs (see Type Keywords).
Some type symbols do not use any arguments; those are called
simple types. For a simple type, if you do not use any
keyword-value pairs, you can omit the parentheses around the type
symbol. For example just string as a customization type is
equivalent to (string).
All customization types are implemented as widgets; see Introduction, for details.
This section describes all the simple customization types. For several of these customization types, the customization widget provides inline completion with C-M-i or M-<TAB>.
sexpsexp as a fall-back for any option, if you don't
want to take the time to work out a more specific type to use.
integernumberfloatstringregexpstring except that the string must be a valid regular
expression.
characterfile(file :must-match t)directoryhook:options keyword in a
hook variable's defcustom to specify a list of functions
recommended for use in the hook; See Variable Definitions.
symbolfunctionvariablefacebooleannil or t. Note that by
using choice and const together (see the next section),
you can specify that the value must be nil or t, but also
specify the text to describe each value in a way that fits the specific
meaning of the alternative.
key-sequencecoding-systemcolorWhen none of the simple types is appropriate, you can use composite types, which build new types from other types or from specified data. The specified types or data are called the arguments of the composite type. The composite type normally looks like this:
(constructor arguments...)
but you can also add keyword-value pairs before the arguments, like this:
(constructor {keyword value}... arguments...)
Here is a table of constructors and how to use them to write composite types:
(cons car-type cdr-type)
(cons string
symbol) is a customization type which matches values such as
("foo" . foo).
In the customization buffer, the car and cdr are displayed
and edited separately, each according to their specified type.
(list element-types...)
For example, (list integer string function) describes a list of
three elements; the first element must be an integer, the second a
string, and the third a function.
In the customization buffer, each element is displayed and edited
separately, according to the type specified for it.
(group element-types...)
list except for the formatting
of text in the Custom buffer. list labels each
element value with its tag; group does not.
(vector element-types...)
list except that the value must be a vector instead of a
list. The elements work the same as in list.
(alist :key-type key-type :value-type value-type)
If omitted, key-type and value-type default to
sexp.
The user can add any key matching the specified key type, but you can
give some keys a preferential treatment by specifying them with the
:options (see Variable Definitions). The specified keys
will always be shown in the customize buffer (together with a suitable
value), with a checkbox to include or exclude or disable the key/value
pair from the alist. The user will not be able to edit the keys
specified by the :options keyword argument.
The argument to the :options keywords should be a list of
specifications for reasonable keys in the alist. Ordinarily, they are
simply atoms, which stand for themselves. For example:
:options '("foo" "bar" "baz")
specifies that there are three known keys, namely "foo",
"bar" and "baz", which will always be shown first.
You may want to restrict the value type for specific keys, for
example, the value associated with the "bar" key can only be an
integer. You can specify this by using a list instead of an atom in
the list. The first element will specify the key, like before, while
the second element will specify the value type. For example:
:options '("foo" ("bar" integer) "baz")
Finally, you may want to change how the key is presented. By default,
the key is simply shown as a const, since the user cannot change
the special keys specified with the :options keyword. However,
you may want to use a more specialized type for presenting the key, like
function-item if you know it is a symbol with a function binding.
This is done by using a customization type specification instead of a
symbol for the key.
:options '("foo"
((function-item some-function) integer)
"baz")
Many alists use lists with two elements, instead of cons cells. For example,
(defcustom list-alist
'(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE).")
instead of
(defcustom cons-alist
'(("foo" . 1) ("bar" . 2) ("baz" . 3))
"Each element is a cons-cell (KEY . VALUE).")
Because of the way lists are implemented on top of cons cells, you can
treat list-alist in the example above as a cons cell alist, where
the value type is a list with a single element containing the real
value.
(defcustom list-alist '(("foo" 1) ("bar" 2) ("baz" 3))
"Each element is a list of the form (KEY VALUE)."
:type '(alist :value-type (group integer)))
The group widget is used here instead of list only because
the formatting is better suited for the purpose.
Similarly, you can have alists with more values associated with each key, using variations of this trick:
(defcustom person-data '(("brian" 50 t)
("dorith" 55 nil)
("ken" 52 t))
"Alist of basic info about people.
Each element has the form (NAME AGE MALE-FLAG)."
:type '(alist :value-type (group integer boolean)))
(plist :key-type key-type :value-type value-type)
alist (see above), except
that (i) the information is stored as a property list,
(see Property Lists), and (ii) key-type, if omitted,
defaults to symbol rather than sexp.
(choice alternative-types...)
(choice integer string) allows either an integer or a string.
In the customization buffer, the user selects an alternative using a menu, and can then edit the value in the usual way for that alternative.
Normally the strings in this menu are determined automatically from the
choices; however, you can specify different strings for the menu by
including the :tag keyword in the alternatives. For example, if
an integer stands for a number of spaces, while a string is text to use
verbatim, you might write the customization type this way,
(choice (integer :tag "Number of spaces")
(string :tag "Literal text"))
so that the menu offers `Number of spaces' and `Literal text'.
In any alternative for which nil is not a valid value, other than
a const, you should specify a valid default for that alternative
using the :value keyword. See Type Keywords.
If some values are covered by more than one of the alternatives, customize will choose the first alternative that the value fits. This means you should always list the most specific types first, and the most general last. Here's an example of proper usage:
(choice (const :tag "Off" nil)
symbol (sexp :tag "Other"))
This way, the special value nil is not treated like other
symbols, and symbols are not treated like other Lisp expressions.
(radio element-types...)
choice, except that the choices are displayed
using radio buttons rather than a menu. This has the advantage of
displaying documentation for the choices when applicable and so is often
a good choice for a choice between constant functions
(function-item customization types).
(const value)
The main use of const is inside of choice. For example,
(choice integer (const nil)) allows either an integer or
nil.
:tag is often used with const, inside of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(const :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and foo means “ask”.
(other value)
The main use of other is as the last element of choice.
For example,
(choice (const :tag "Yes" t)
(const :tag "No" nil)
(other :tag "Ask" foo))
describes a variable for which t means yes, nil means no,
and anything else means “ask”. If the user chooses `Ask' from
the menu of alternatives, that specifies the value foo; but any
other value (not t, nil or foo) displays as
`Ask', just like foo.
(function-item function)
const, but used for values which are functions. This
displays the documentation string as well as the function name.
The documentation string is either the one you specify with
:doc, or function's own documentation string.
(variable-item variable)
const, but used for values which are variable names. This
displays the documentation string as well as the variable name. The
documentation string is either the one you specify with :doc, or
variable's own documentation string.
(set types...)
This appears in the customization buffer as a checklist, so that each of
types may have either one corresponding element or none. It is
not possible to specify two different elements that match the same one
of types. For example, (set integer symbol) allows one
integer and/or one symbol in the list; it does not allow multiple
integers or multiple symbols. As a result, it is rare to use
nonspecific types such as integer in a set.
Most often, the types in a set are const types, as
shown here:
(set (const :bold) (const :italic))
Sometimes they describe possible elements in an alist:
(set (cons :tag "Height" (const height) integer)
(cons :tag "Width" (const width) integer))
That lets the user specify a height value optionally
and a width value optionally.
(repeat element-type)
(restricted-sexp :match-alternatives criteria)
nil or non-nil according to
the argument. Using a predicate in the list says that objects for which
the predicate returns non-nil are acceptable.
'object. This sort of element
in the list says that object itself is an acceptable value.
For example,
(restricted-sexp :match-alternatives
(integerp 't 'nil))
allows integers, t and nil as legitimate values.
The customization buffer shows all legitimate values using their read syntax, and the user edits them textually.
Here is a table of the keywords you can use in keyword-value pairs in a composite type:
:tag tag
choice.
:match-alternatives criteria
restricted-sexp.
:args argument-list
(const :args (foo)) is equivalent to
(const foo). You rarely need to write :args explicitly,
because normally the arguments are recognized automatically as
whatever follows the last keyword-value pair.
The :inline feature lets you splice a variable number of
elements into the middle of a list or vector
customization type. You use it by adding :inline t to a type
specification which is contained in a list or vector
specification.
Normally, each entry in a list or vector type
specification describes a single element type. But when an entry
contains :inline t, the value it matches is merged directly
into the containing sequence. For example, if the entry matches a
list with three elements, those become three elements of the overall
sequence. This is analogous to `,@' in a backquote construct
(see Backquote).
For example, to specify a list whose first element must be baz
and whose remaining arguments should be zero or more of foo and
bar, use this customization type:
(list (const baz) (set :inline t (const foo) (const bar)))
This matches values such as (baz), (baz foo), (baz bar)
and (baz foo bar).
When the element-type is a choice, you use :inline not
in the choice itself, but in (some of) the alternatives of the
choice. For example, to match a list which must start with a
file name, followed either by the symbol t or two strings, use
this customization type:
(list file
(choice (const t)
(list :inline t string string)))
If the user chooses the first alternative in the choice, then the
overall list has two elements and the second element is t. If
the user chooses the second alternative, then the overall list has three
elements and the second and third must be strings.
You can specify keyword-argument pairs in a customization type after the type name symbol. Here are the keywords you can use, and their meanings:
:value default
If nil is not a valid value for the alternative, then it is
essential to specify a valid default with :value.
If you use this for a type that appears as an alternative inside of
choice; it specifies the default value to use, at first, if and
when the user selects this alternative with the menu in the
customization buffer.
Of course, if the actual value of the option fits this alternative, it
will appear showing the actual value, not default.
:format format-string
:action
attribute specifies what the button will do if the user invokes it;
its value is a function which takes two arguments—the widget which
the button appears in, and the event.
There is no way to specify two different buttons with different
actions.
:sample-face.
:tag
keyword.
:action action
:button-face face
:button-prefix prefix:button-suffix suffix
nil:tag tag
:doc doc
:format, and use `%d' or `%h'
in that value.
The usual reason to specify a documentation string for a type is to
provide more information about the meanings of alternatives inside a
:choice type or the parts of some other composite type.
:help-echo motion-doc
widget-forward or
widget-backward, it will display the string motion-doc in
the echo area. In addition, motion-doc is used as the mouse
help-echo string and may actually be a function or form evaluated
to yield a help string. If it is a function, it is called with one
argument, the widget.
:match function
nil if
the value is acceptable.
:validate function
nil if the widget's
current value is valid for the widget. Otherwise, it should return
the widget containing the invalid data, and set that widget's
:error property to a string explaining the error.
In the previous sections we have described how to construct elaborate
type specifications for defcustom. In some cases you may want
to give such a type specification a name. The obvious case is when
you are using the same type for many user options: rather than repeat
the specification for each option, you can give the type specification
a name, and use that name each defcustom. The other case is
when a user option's value is a recursive data structure. To make it
possible for a datatype to refer to itself, it needs to have a name.
Since custom types are implemented as widgets, the way to define a new customize type is to define a new widget. We are not going to describe the widget interface here in details, see Introduction, for that. Instead we are going to demonstrate the minimal functionality needed for defining new customize types by a simple example.
(define-widget 'binary-tree-of-string 'lazy
"A binary tree made of cons-cells and strings."
:offset 4
:tag "Node"
:type '(choice (string :tag "Leaf" :value "")
(cons :tag "Interior"
:value ("" . "")
binary-tree-of-string
binary-tree-of-string)))
(defcustom foo-bar ""
"Sample variable holding a binary tree of strings."
:type 'binary-tree-of-string)
The function to define a new widget is called define-widget. The
first argument is the symbol we want to make a new widget type. The
second argument is a symbol representing an existing widget, the new
widget is going to be defined in terms of difference from the existing
widget. For the purpose of defining new customization types, the
lazy widget is perfect, because it accepts a :type keyword
argument with the same syntax as the keyword argument to
defcustom with the same name. The third argument is a
documentation string for the new widget. You will be able to see that
string with the M-x widget-browse <RET> binary-tree-of-string
<RET> command.
After these mandatory arguments follow the keyword arguments. The most
important is :type, which describes the data type we want to match
with this widget. Here a binary-tree-of-string is described as
being either a string, or a cons-cell whose car and cdr are themselves
both binary-tree-of-string. Note the reference to the widget
type we are currently in the process of defining. The :tag
attribute is a string to name the widget in the user interface, and the
:offset argument is there to ensure that child nodes are
indented four spaces relative to the parent node, making the tree
structure apparent in the customization buffer.
The defcustom shows how the new widget can be used as an ordinary
customization type.
The reason for the name lazy is that the other composite
widgets convert their inferior widgets to internal form when the
widget is instantiated in a buffer. This conversion is recursive, so
the inferior widgets will convert their inferior widgets. If
the data structure is itself recursive, this conversion is an infinite
recursion. The lazy widget prevents the recursion: it convert
its :type argument only when needed.
The following functions are responsible for installing the user's
customization settings for variables and faces, respectively. When
the user invokes `Save for future sessions' in the Customize
interface, that takes effect by writing a custom-set-variables
and/or a custom-set-faces form into the custom file, to be
evaluated the next time Emacs starts.
This function installs the variable customizations specified by args. Each argument in args should have the form
(var expression [now [request [comment]]])var is a variable name (a symbol), and expression is an expression which evaluates to the desired customized value.
If the
defcustomform for var has been evaluated prior to thiscustom-set-variablescall, expression is immediately evaluated, and the variable's value is set to the result. Otherwise, expression is stored into the variable'ssaved-valueproperty, to be evaluated when the relevantdefcustomis called (usually when the library defining that variable is loaded into Emacs).The now, request, and comment entries are for internal use only, and may be omitted. now, if non-
nil, means to set the variable's value now, even if the variable'sdefcustomform has not been evaluated. request is a list of features to be loaded immediately (see Named Features). comment is a string describing the customization.
This function installs the face customizations specified by args. Each argument in args should have the form
(face spec [now [comment]])face is a face name (a symbol), and spec is the customized face specification for that face (see Defining Faces).
The now and comment entries are for internal use only, and may be omitted. now, if non-
nil, means to install the face specification now, even if thedeffaceform has not been evaluated. comment is a string describing the customization.
Custom themes are collections of settings that can be enabled or disabled as a unit. See Custom Themes. Each Custom theme is defined by an Emacs Lisp source file, which should follow the conventions described in this section. (Instead of writing a Custom theme by hand, you can also create one using a Customize-like interface; see Creating Custom Themes.)
A Custom theme file should be named foo-theme.el, where
foo is the theme name. The first Lisp form in the file should
be a call to deftheme, and the last form should be a call to
provide-theme.
This macro declares theme (a symbol) as the name of a Custom theme. The optional argument doc should be a string describing the theme; this is the description shown when the user invokes the
describe-themecommand or types ? in the `*Custom Themes*' buffer.Two special theme names are disallowed (using them causes an error):
useris a dummy theme that stores the user's direct customization settings, andchangedis a dummy theme that stores changes made outside of the Customize system.
This macro declares that the theme named theme has been fully specified.
In between deftheme and provide-theme are Lisp forms
specifying the theme settings: usually a call to
custom-theme-set-variables and/or a call to
custom-theme-set-faces.
This function specifies the Custom theme theme's variable settings. theme should be a symbol. Each argument in args should be a list of the form
(var expression [now [request [comment]]])where the list entries have the same meanings as in
custom-set-variables. See Applying Customizations.
This function specifies the Custom theme theme's face settings. theme should be a symbol. Each argument in args should be a list of the form
(face spec [now [comment]])where the list entries have the same meanings as in
custom-set-faces. See Applying Customizations.
In theory, a theme file can also contain other Lisp forms, which would be evaluated when loading the theme, but that is bad form. To protect against loading themes containing malicious code, Emacs displays the source file and asks for confirmation from the user before loading any non-built-in theme for the first time.
The following functions are useful for programmatically enabling and disabling themes:
This function return a non-
nilvalue if theme (a symbol) is the name of a Custom theme (i.e., a Custom theme which has been loaded into Emacs, whether or not the theme is enabled). Otherwise, it returnsnil.
The value of this variable is a list of themes loaded into Emacs. Each theme is represented by a Lisp symbol (the theme name). The default value of this variable is a list containing two dummy themes:
(user changed). Thechangedtheme stores settings made before any Custom themes are applied (e.g., variables set outside of Customize). Theusertheme stores settings the user has customized and saved. Any additional themes declared with thedefthememacro are added to the front of this list.
This function loads the Custom theme named theme from its source file, looking for the source file in the directories specified by the variable
custom-theme-load-path. See Custom Themes. It also enables the theme (unless the optional argument no-enable is non-nil), causing its variable and face settings to take effect. It prompts the user for confirmation before loading the theme, unless the optional argument no-confirm is non-nil.
This function enables the Custom theme named theme. It signals an error if no such theme has been loaded.
This function disables the Custom theme named theme. The theme remains loaded, so that a subsequent call to
enable-themewill re-enable it.
Loading a file of Lisp code means bringing its contents into the Lisp environment in the form of Lisp objects. Emacs finds and opens the file, reads the text, evaluates each form, and then closes the file. Such a file is also called a Lisp library.
The load functions evaluate all the expressions in a file just
as the eval-buffer function evaluates all the
expressions in a buffer. The difference is that the load functions
read and evaluate the text in the file as found on disk, not the text
in an Emacs buffer.
The loaded file must contain Lisp expressions, either as source code or as byte-compiled code. Each form in the file is called a top-level form. There is no special format for the forms in a loadable file; any form in a file may equally well be typed directly into a buffer and evaluated there. (Indeed, most code is tested this way.) Most often, the forms are function definitions and variable definitions.
Emacs can also load compiled dynamic modules: shared libraries that provide additional functionality for use in Emacs Lisp programs, just like a package written in Emacs Lisp would. When a dynamic module is loaded, Emacs calls a specially-named initialization function which the module needs to implement, and which exposes the additional functions and variables to Emacs Lisp programs.
For on-demand loading of external libraries which are known in advance to be required by certain Emacs primitives, see Dynamic Libraries.
Emacs Lisp has several interfaces for loading. For example,
autoload creates a placeholder object for a function defined in a
file; trying to call the autoloading function loads the file to get the
function's real definition (see Autoload). require loads a
file if it isn't already loaded (see Named Features). Ultimately,
all these facilities call the load function to do the work.
This function finds and opens a file of Lisp code, evaluates all the forms in it, and closes the file.
To find the file,
loadfirst looks for a file named filename.elc, that is, for a file whose name is filename with the extension `.elc' appended. If such a file exists, it is loaded. If there is no file by that name, thenloadlooks for a file named filename.el. If that file exists, it is loaded. If Emacs was compiled with support for dynamic modules (see Dynamic Modules),loadnext looks for a file named filename.ext, where ext is a system-dependent file-name extension of shared libraries. Finally, if neither of those names is found,loadlooks for a file named filename with nothing appended, and loads it if it exists. (Theloadfunction is not clever about looking at filename. In the perverse case of a file named foo.el.el, evaluation of(load "foo.el")will indeed find it.)If Auto Compression mode is enabled, as it is by default, then if
loadcan not find a file, it searches for a compressed version of the file before trying other file names. It decompresses and loads it if it exists. It looks for compressed versions by appending each of the suffixes injka-compr-load-suffixesto the file name. The value of this variable must be a list of strings. Its standard value is(".gz").If the optional argument nosuffix is non-
nil, thenloaddoes not try the suffixes `.elc' and `.el'. In this case, you must specify the precise file name you want, except that, if Auto Compression mode is enabled,loadwill still usejka-compr-load-suffixesto find compressed versions. By specifying the precise file name and usingtfor nosuffix, you can prevent file names like foo.el.el from being tried.If the optional argument must-suffix is non-
nil, thenloadinsists that the file name used must end in either `.el' or `.elc' (possibly extended with a compression suffix) or the shared-library extension, unless it contains an explicit directory name.If the option
load-prefer-neweris non-nil, then when searching suffixes,loadselects whichever version of a file (`.elc', `.el', etc.) has been modified most recently.If filename is a relative file name, such as foo or baz/foo.bar,
loadsearches for the file using the variableload-path. It appends filename to each of the directories listed inload-path, and loads the first file it finds whose name matches. The current default directory is tried only if it is specified inload-path, wherenilstands for the default directory.loadtries all three possible suffixes in the first directory inload-path, then all three suffixes in the second directory, and so on. See Library Search.Whatever the name under which the file is eventually found, and the directory where Emacs found it, Emacs sets the value of the variable
load-file-nameto that file's name.If you get a warning that foo.elc is older than foo.el, it means you should consider recompiling foo.el. See Byte Compilation.
When loading a source file (not compiled),
loadperforms character set translation just as Emacs would do when visiting the file. See Coding Systems.When loading an uncompiled file, Emacs tries to expand any macros that the file contains (see Macros). We refer to this as eager macro expansion. Doing this (rather than deferring the expansion until the relevant code runs) can significantly speed up the execution of uncompiled code. Sometimes, this macro expansion cannot be done, owing to a cyclic dependency. In the simplest example of this, the file you are loading refers to a macro defined in another file, and that file in turn requires the file you are loading. This is generally harmless. Emacs prints a warning (`Eager macro-expansion skipped due to cycle...') giving details of the problem, but it still loads the file, just leaving the macro unexpanded for now. You may wish to restructure your code so that this does not happen. Loading a compiled file does not cause macroexpansion, because this should already have happened during compilation. See Compiling Macros.
Messages like `Loading foo...' and `Loading foo...done' appear in the echo area during loading unless nomessage is non-
nil.Any unhandled errors while loading a file terminate loading. If the load was done for the sake of
autoload, any function definitions made during the loading are undone.If
loadcan't find the file to load, then normally it signals the errorfile-error(with `Cannot open load file filename'). But if missing-ok is non-nil, thenloadjust returnsnil.You can use the variable
load-read-functionto specify a function forloadto use instead ofreadfor reading expressions. See below.
loadreturnstif the file loads successfully.
This command loads the file filename. If filename is a relative file name, then the current default directory is assumed. This command does not use
load-path, and does not append suffixes. However, it does look for compressed versions (if Auto Compression Mode is enabled). Use this command if you wish to specify precisely the file name to load.
This command loads the library named library. It is equivalent to
load, except for the way it reads its argument interactively. See Lisp Libraries.
This variable is non-
nilif Emacs is in the process of loading a file, and it isnilotherwise.
When Emacs is in the process of loading a file, this variable's value is the name of that file, as Emacs found it during the search described earlier in this section.
This variable specifies an alternate expression-reading function for
loadandeval-regionto use instead ofread. The function should accept one argument, just asreaddoes.By default, this variable's value is
read. See Input Functions.Instead of using this variable, it is cleaner to use another, newer feature: to pass the function as the read-function argument to
eval-region. See Eval.
For information about how load is used in building Emacs, see
Building Emacs.
We now describe some technical details about the exact suffixes that
load tries.
This is a list of suffixes indicating (compiled or source) Emacs Lisp files. It should not include the empty string.
loaduses these suffixes in order when it appends Lisp suffixes to the specified file name. The standard value is(".elc" ".el")which produces the behavior described in the previous section.
This is a list of suffixes that indicate representations of the same file. This list should normally start with the empty string. When
loadsearches for a file it appends the suffixes in this list, in order, to the file name, before searching for another file.Enabling Auto Compression mode appends the suffixes in
jka-compr-load-suffixesto this list and disabling Auto Compression mode removes them again. The standard value ofload-file-rep-suffixesif Auto Compression mode is disabled is(""). Given that the standard value ofjka-compr-load-suffixesis(".gz"), the standard value ofload-file-rep-suffixesif Auto Compression mode is enabled is("" ".gz").
This function returns the list of all suffixes that
loadshould try, in order, when its must-suffix argument is non-nil. This takes bothload-suffixesandload-file-rep-suffixesinto account. Ifload-suffixes,jka-compr-load-suffixesandload-file-rep-suffixesall have their standard values, this function returns(".elc" ".elc.gz" ".el" ".el.gz")if Auto Compression mode is enabled and(".elc" ".el")if Auto Compression mode is disabled.
To summarize, load normally first tries the suffixes in the
value of (get-load-suffixes) and then those in
load-file-rep-suffixes. If nosuffix is non-nil,
it skips the former group, and if must-suffix is non-nil,
it skips the latter group.
If this option is non-
nil, then rather than stopping at the first suffix that exists,loadtests them all, and uses whichever file is the newest.
When Emacs loads a Lisp library, it searches for the library
in a list of directories specified by the variable load-path.
The value of this variable is a list of directories to search when loading files with
load. Each element is a string (which must be a directory name) ornil(which stands for the current working directory).
When Emacs starts up, it sets up the value of load-path
in several steps. First, it initializes load-path using
default locations set when Emacs was compiled. Normally, this
is a directory something like
"/usr/local/share/emacs/version/lisp"
(In this and the following examples, replace /usr/local with the installation prefix appropriate for your Emacs.) These directories contain the standard Lisp files that come with Emacs. If Emacs cannot find them, it will not start correctly.
If you run Emacs from the directory where it was built—that is, an
executable that has not been formally installed—Emacs instead
initializes load-path using the lisp
directory in the directory containing the sources from which it
was built.
If you built Emacs in a separate directory from the
sources, it also adds the lisp directories from the build directory.
(In all cases, elements are represented as absolute file names.)
Unless you start Emacs with the --no-site-lisp option,
it then adds two more site-lisp directories to the front of
load-path. These are intended for locally installed Lisp files,
and are normally of the form:
"/usr/local/share/emacs/version/site-lisp"
and
"/usr/local/share/emacs/site-lisp"
The first one is for locally installed files for a specific Emacs version; the second is for locally installed files meant for use with all installed Emacs versions. (If Emacs is running uninstalled, it also adds site-lisp directories from the source and build directories, if they exist. Normally these directories do not contain site-lisp directories.)
If the environment variable EMACSLOADPATH is set, it modifies
the above initialization procedure. Emacs initializes
load-path based on the value of the environment variable.
The syntax of EMACSLOADPATH is the same as used for PATH;
directory names are separated by `:' (or `;', on some
operating systems).
Here is an example of how to set EMACSLOADPATH variable (from a
sh-style shell):
export EMACSLOADPATH=/home/foo/.emacs.d/lisp:
An empty element in the value of the environment variable, whether
trailing (as in the above example), leading, or embedded, is replaced
by the default value of load-path as determined by the standard
initialization procedure. If there are no such empty elements, then
EMACSLOADPATH specifies the entire load-path. You must
include either an empty element, or the explicit path to the directory
containing the standard Lisp files, else Emacs will not function.
(Another way to modify load-path is to use the -L
command-line option when starting Emacs; see below.)
For each directory in load-path, Emacs then checks to see if
it contains a file subdirs.el, and if so, loads it. The
subdirs.el file is created when Emacs is built/installed,
and contains code that causes Emacs to add any subdirectories of those
directories to load-path. Both immediate subdirectories and
subdirectories multiple levels down are added. But it excludes
subdirectories whose names do not start with a letter or digit, and
subdirectories named RCS or CVS, and subdirectories
containing a file named .nosearch.
Next, Emacs adds any extra load directories that you specify using the -L command-line option (see Action Arguments). It also adds the directories where optional packages are installed, if any (see Packaging Basics).
It is common to add code to one's init file (see Init File) to
add one or more directories to load-path. For example:
(push "~/.emacs.d/lisp" load-path)
Dumping Emacs uses a special value of load-path. If you use
a site-load.el or site-init.el file to customize the
dumped Emacs (see Building Emacs), any changes to load-path
that these files make will be lost after dumping.
This command finds the precise file name for library library. It searches for the library in the same way
loaddoes, and the argument nosuffix has the same meaning as inload: don't add suffixes `.elc' or `.el' to the specified name library.If the path is non-
nil, that list of directories is used instead ofload-path.When
locate-libraryis called from a program, it returns the file name as a string. When the user runslocate-libraryinteractively, the argument interactive-call ist, and this tellslocate-libraryto display the file name in the echo area.
This command shows a list of shadowed Emacs Lisp files. A shadowed file is one that will not normally be loaded, despite being in a directory on
load-path, due to the existence of another similarly-named file in a directory earlier onload-path.For instance, suppose
load-pathis set to("/opt/emacs/site-lisp" "/usr/share/emacs/23.3/lisp")and that both these directories contain a file named foo.el. Then
(require 'foo)never loads the file in the second directory. Such a situation might indicate a problem in the way Emacs was installed.When called from Lisp, this function prints a message listing the shadowed files, instead of displaying them in a buffer. If the optional argument
stringpis non-nil, it instead returns the shadowed files as a string.
When Emacs Lisp programs contain string constants with non-ASCII characters, these can be represented within Emacs either as unibyte strings or as multibyte strings (see Text Representations). Which representation is used depends on how the file is read into Emacs. If it is read with decoding into multibyte representation, the text of the Lisp program will be multibyte text, and its string constants will be multibyte strings. If a file containing Latin-1 characters (for example) is read without decoding, the text of the program will be unibyte text, and its string constants will be unibyte strings. See Coding Systems.
In most Emacs Lisp programs, the fact that non-ASCII
strings are multibyte strings should not be noticeable, since
inserting them in unibyte buffers converts them to unibyte
automatically. However, if this does make a difference, you can force
a particular Lisp file to be interpreted as unibyte by writing
`coding: raw-text' in a local variables section. With
that designator, the file will unconditionally be interpreted as
unibyte. This can matter when making keybindings to
non-ASCII characters written as ?vliteral.
The autoload facility lets you register the existence of a function or macro, but put off loading the file that defines it. The first call to the function automatically loads the proper library, in order to install the real definition and other associated code, then runs the real definition as if it had been loaded all along. Autoloading can also be triggered by looking up the documentation of the function or macro (see Documentation Basics).
There are two ways to set up an autoloaded function: by calling
autoload, and by writing a “magic” comment in the
source before the real definition. autoload is the low-level
primitive for autoloading; any Lisp program can call autoload at
any time. Magic comments are the most convenient way to make a function
autoload, for packages installed along with Emacs. These comments do
nothing on their own, but they serve as a guide for the command
update-file-autoloads, which constructs calls to autoload
and arranges to execute them when Emacs is built.
This function defines the function (or macro) named function so as to load automatically from filename. The string filename specifies the file to load to get the real definition of function.
If filename does not contain either a directory name, or the suffix
.elor.elc, this function insists on adding one of these suffixes, and it will not load from a file whose name is just filename with no added suffix. (The variableload-suffixesspecifies the exact required suffixes.)The argument docstring is the documentation string for the function. Specifying the documentation string in the call to
autoloadmakes it possible to look at the documentation without loading the function's real definition. Normally, this should be identical to the documentation string in the function definition itself. If it isn't, the function definition's documentation string takes effect when it is loaded.If interactive is non-
nil, that says function can be called interactively. This lets completion in M-x work without loading function's real definition. The complete interactive specification is not given here; it's not needed unless the user actually calls function, and when that happens, it's time to load the real definition.You can autoload macros and keymaps as well as ordinary functions. Specify type as
macroif function is really a macro. Specify type askeymapif function is really a keymap. Various parts of Emacs need to know this information without loading the real definition.An autoloaded keymap loads automatically during key lookup when a prefix key's binding is the symbol function. Autoloading does not occur for other kinds of access to the keymap. In particular, it does not happen when a Lisp program gets the keymap from the value of a variable and calls
define-key; not even if the variable name is the same symbol function.If function already has a non-void function definition that is not an autoload object, this function does nothing and returns
nil. Otherwise, it constructs an autoload object (see Autoload Type), and stores it as the function definition for function. The autoload object has this form:(autoload filename docstring interactive type)For example,
(symbol-function 'run-prolog) => (autoload "prolog" 169681 t nil)In this case,
"prolog"is the name of the file to load, 169681 refers to the documentation string in the emacs/etc/DOC file (see Documentation Basics),tmeans the function is interactive, andnilthat it is not a macro or a keymap.
This function returns non-
nilif object is an autoload object. For example, to check ifrun-prologis defined as an autoloaded function, evaluate(autoloadp (symbol-function 'run-prolog))
The autoloaded file usually contains other definitions and may require
or provide one or more features. If the file is not completely loaded
(due to an error in the evaluation of its contents), any function
definitions or provide calls that occurred during the load are
undone. This is to ensure that the next attempt to call any function
autoloading from this file will try again to load the file. If not for
this, then some of the functions in the file might be defined by the
aborted load, but fail to work properly for the lack of certain
subroutines not loaded successfully because they come later in the file.
If the autoloaded file fails to define the desired Lisp function or
macro, then an error is signaled with data "Autoloading failed to
define function function-name".
A magic autoload comment (often called an autoload cookie)
consists of `;;;###autoload', on a line by itself,
just before the real definition of the function in its
autoloadable source file. The command M-x update-file-autoloads
writes a corresponding autoload call into loaddefs.el.
(The string that serves as the autoload cookie and the name of the
file generated by update-file-autoloads can be changed from the
above defaults, see below.)
Building Emacs loads loaddefs.el and thus calls autoload.
M-x update-directory-autoloads is even more powerful; it updates
autoloads for all files in the current directory.
The same magic comment can copy any kind of form into
loaddefs.el. The form following the magic comment is copied
verbatim, except if it is one of the forms which the autoload
facility handles specially (e.g., by conversion into an
autoload call). The forms which are not copied verbatim are
the following:
defun and defmacro; also cl-defun and
cl-defmacro (see Argument Lists),
and define-overloadable-function (see the commentary in
mode-local.el).
define-minor-mode, define-globalized-minor-mode,
define-generic-mode, define-derived-mode,
easy-mmode-define-minor-mode,
easy-mmode-define-global-mode, define-compilation-mode,
and define-global-minor-mode.
defcustom, defgroup, defclass
(see EIEIO), and define-skeleton (see the
commentary in skeleton.el).
You can also use a magic comment to execute a form at build time without executing it when the file itself is loaded. To do this, write the form on the same line as the magic comment. Since it is in a comment, it does nothing when you load the source file; but M-x update-file-autoloads copies it to loaddefs.el, where it is executed while building Emacs.
The following example shows how doctor is prepared for
autoloading with a magic comment:
;;;###autoload
(defun doctor ()
"Switch to *doctor* buffer and start giving psychotherapy."
(interactive)
(switch-to-buffer "*doctor*")
(doctor-mode))
Here's what that produces in loaddefs.el:
(autoload (quote doctor) "doctor" "\
Switch to *doctor* buffer and start giving psychotherapy.
\(fn)" t nil)
The backslash and newline immediately following the double-quote are a
convention used only in the preloaded uncompiled Lisp files such as
loaddefs.el; they tell make-docfile to put the
documentation string in the etc/DOC file. See Building Emacs.
See also the commentary in lib-src/make-docfile.c. `(fn)'
in the usage part of the documentation string is replaced with the
function's name when the various help functions (see Help Functions) display it.
If you write a function definition with an unusual macro that is not
one of the known and recognized function definition methods, use of an
ordinary magic autoload comment would copy the whole definition into
loaddefs.el. That is not desirable. You can put the desired
autoload call into loaddefs.el instead by writing this:
;;;###autoload (autoload 'foo "myfile")
(mydefunmacro foo
...)
You can use a non-default string as the autoload cookie and have the corresponding autoload calls written into a file whose name is different from the default loaddefs.el. Emacs provides two variables to control this:
The value of this variable should be a string whose syntax is a Lisp comment. M-x update-file-autoloads copies the Lisp form that follows the cookie into the autoload file it generates. The default value of this variable is
";;;###autoload".
The value of this variable names an Emacs Lisp file where the autoload calls should go. The default value is loaddefs.el, but you can override that, e.g., in the local variables section of a .el file (see File Local Variables). The autoload file is assumed to contain a trailer starting with a formfeed character.
The following function may be used to explicitly load the library specified by an autoload object:
This function performs the loading specified by autoload, which should be an autoload object. The optional argument name, if non-
nil, should be a symbol whose function value is autoload; in that case, the return value of this function is the symbol's new function value. If the value of the optional argument macro-only ismacro, this function avoids loading a function, only a macro.
You can load a given file more than once in an Emacs session. For example, after you have rewritten and reinstalled a function definition by editing it in a buffer, you may wish to return to the original version; you can do this by reloading the file it came from.
When you load or reload files, bear in mind that the load and
load-library functions automatically load a byte-compiled file
rather than a non-compiled file of similar name. If you rewrite a file
that you intend to save and reinstall, you need to byte-compile the new
version; otherwise Emacs will load the older, byte-compiled file instead
of your newer, non-compiled file! If that happens, the message
displayed when loading the file includes, `(compiled; note, source is
newer)', to remind you to recompile it.
When writing the forms in a Lisp library file, keep in mind that the
file might be loaded more than once. For example, think about whether
each variable should be reinitialized when you reload the library;
defvar does not change the value if the variable is already
initialized. (See Defining Variables.)
The simplest way to add an element to an alist is like this:
(push '(leif-mode " Leif") minor-mode-alist)
But this would add multiple elements if the library is reloaded. To
avoid the problem, use add-to-list (see List Variables):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
Occasionally you will want to test explicitly whether a library has
already been loaded. If the library uses provide to provide a
named feature, you can use featurep earlier in the file to test
whether the provide call has been executed before (see Named Features). Alternatively, you could use something like this:
(defvar foo-was-loaded nil)
(unless foo-was-loaded
execute-first-time-only
(setq foo-was-loaded t))
provide and require are an alternative to
autoload for loading files automatically. They work in terms of
named features. Autoloading is triggered by calling a specific
function, but a feature is loaded the first time another program asks
for it by name.
A feature name is a symbol that stands for a collection of functions, variables, etc. The file that defines them should provide the feature. Another program that uses them may ensure they are defined by requiring the feature. This loads the file of definitions if it hasn't been loaded already.
To require the presence of a feature, call require with the
feature name as argument. require looks in the global variable
features to see whether the desired feature has been provided
already. If not, it loads the feature from the appropriate file. This
file should call provide at the top level to add the feature to
features; if it fails to do so, require signals an error.
For example, in idlwave.el, the definition for
idlwave-complete-filename includes the following code:
(defun idlwave-complete-filename ()
"Use the comint stuff to complete a file name."
(require 'comint)
(let* ((comint-file-name-chars "~/A-Za-z0-9+@:_.$#%={}\\-")
(comint-completion-addsuffix nil)
...)
(comint-dynamic-complete-filename)))
The expression (require 'comint) loads the file comint.el
if it has not yet been loaded, ensuring that
comint-dynamic-complete-filename is defined. Features are
normally named after the files that provide them, so that
require need not be given the file name. (Note that it is
important that the require statement be outside the body of the
let. Loading a library while its variables are let-bound can
have unintended consequences, namely the variables becoming unbound
after the let exits.)
The comint.el file contains the following top-level expression:
(provide 'comint)
This adds comint to the global features list, so that
(require 'comint) will henceforth know that nothing needs to be
done.
When require is used at top level in a file, it takes effect
when you byte-compile that file (see Byte Compilation) as well as
when you load it. This is in case the required package contains macros
that the byte compiler must know about. It also avoids byte compiler
warnings for functions and variables defined in the file loaded with
require.
Although top-level calls to require are evaluated during
byte compilation, provide calls are not. Therefore, you can
ensure that a file of definitions is loaded before it is byte-compiled
by including a provide followed by a require for the same
feature, as in the following example.
(provide 'my-feature) ; Ignored by byte compiler,
; evaluated by load.
(require 'my-feature) ; Evaluated by byte compiler.
The compiler ignores the provide, then processes the
require by loading the file in question. Loading the file does
execute the provide call, so the subsequent require call
does nothing when the file is loaded.
This function announces that feature is now loaded, or being loaded, into the current Emacs session. This means that the facilities associated with feature are or will be available for other Lisp programs.
The direct effect of calling
provideis if not already in features then to add feature to the front of that list and call anyeval-after-loadcode waiting for it (see Hooks for Loading). The argument feature must be a symbol.providereturns feature.If provided, subfeatures should be a list of symbols indicating a set of specific subfeatures provided by this version of feature. You can test the presence of a subfeature using
featurep. The idea of subfeatures is that you use them when a package (which is one feature) is complex enough to make it useful to give names to various parts or functionalities of the package, which might or might not be loaded, or might or might not be present in a given version. See Network Feature Testing, for an example.features => (bar bish) (provide 'foo) => foo features => (foo bar bish)When a file is loaded to satisfy an autoload, and it stops due to an error in the evaluation of its contents, any function definitions or
providecalls that occurred during the load are undone. See Autoload.
This function checks whether feature is present in the current Emacs session (using
(featurepfeature); see below). The argument feature must be a symbol.If the feature is not present, then
requireloads filename withload. If filename is not supplied, then the name of the symbol feature is used as the base file name to load. However, in this case,requireinsists on finding feature with an added `.el' or `.elc' suffix (possibly extended with a compression suffix); a file whose name is just feature won't be used. (The variableload-suffixesspecifies the exact required Lisp suffixes.)If noerror is non-
nil, that suppresses errors from actual loading of the file. In that case,requirereturnsnilif loading the file fails. Normally,requirereturns feature.If loading the file succeeds but does not provide feature,
requiresignals an error, `Required feature feature was not provided'.
This function returns
tif feature has been provided in the current Emacs session (i.e., if feature is a member offeatures.) If subfeature is non-nil, then the function returnstonly if that subfeature is provided as well (i.e., if subfeature is a member of thesubfeatureproperty of the feature symbol.)
The value of this variable is a list of symbols that are the features loaded in the current Emacs session. Each symbol was put in this list with a call to
provide. The order of the elements in thefeatureslist is not significant.
This function returns the name of the file that defined symbol. If type is
nil, then any kind of definition is acceptable. If type isdefun,defvar, ordefface, that specifies function definition, variable definition, or face definition only.The value is normally an absolute file name. It can also be
nil, if the definition is not associated with any file. If symbol specifies an autoloaded function, the value can be a relative file name without extension.
The basis for symbol-file is the data in the variable
load-history.
The value of this variable is an alist that associates the names of loaded library files with the names of the functions and variables they defined, as well as the features they provided or required.
Each element in this alist describes one loaded library (including libraries that are preloaded at startup). It is a list whose car is the absolute file name of the library (a string). The rest of the list elements have these forms:
- var
- The symbol var was defined as a variable.
(defun .fun)- The function fun was defined.
(t .fun)- The function fun was previously an autoload before this library redefined it as a function. The following element is always
(defun .fun), which represents defining fun as a function.
(autoload .fun)- The function fun was defined as an autoload.
(defface .face)- The face face was defined.
(require .feature)- The feature feature was required.
(provide .feature)- The feature feature was provided.
(cl-defmethodmethod specializers)- The named method was defined by using
cl-defmethod, with specializers as its specializers.
(define-type .type)- The type type was defined.
The value of
load-historymay have one element whose car isnil. This element describes definitions made witheval-bufferon a buffer that is not visiting a file.
The command eval-region updates load-history, but does so
by adding the symbols defined to the element for the file being visited,
rather than replacing that element. See Eval.
You can discard the functions and variables loaded by a library to
reclaim memory for other Lisp objects. To do this, use the function
unload-feature:
This command unloads the library that provided feature feature. It undefines all functions, macros, and variables defined in that library with
defun,defalias,defsubst,defmacro,defconst,defvar, anddefcustom. It then restores any autoloads formerly associated with those symbols. (Loading saves these in theautoloadproperty of the symbol.)Before restoring the previous definitions,
unload-featurerunsremove-hookto remove functions in the library from certain hooks. These hooks include variables whose names end in `-hook' (or the deprecated suffix `-hooks'), plus those listed inunload-feature-special-hooks, as well asauto-mode-alist. This is to prevent Emacs from ceasing to function because important hooks refer to functions that are no longer defined.Standard unloading activities also undoes ELP profiling of functions in that library, unprovides any features provided by the library, and cancels timers held in variables defined by the library.
If these measures are not sufficient to prevent malfunction, a library can define an explicit unloader named feature
-unload-function. If that symbol is defined as a function,unload-featurecalls it with no arguments before doing anything else. It can do whatever is appropriate to unload the library. If it returnsnil,unload-featureproceeds to take the normal unload actions. Otherwise it considers the job to be done.Ordinarily,
unload-featurerefuses to unload a library on which other loaded libraries depend. (A library a depends on library b if a contains arequirefor b.) If the optional argument force is non-nil, dependencies are ignored and you can unload any library.
The unload-feature function is written in Lisp; its actions are
based on the variable load-history.
This variable holds a list of hooks to be scanned before unloading a library, to remove functions defined in the library.
You can ask for code to be executed each time Emacs loads a library,
by using the variable after-load-functions:
This abnormal hook is run after loading a file. Each function in the hook is called with a single argument, the absolute filename of the file that was just loaded.
If you want code to be executed when a particular library is
loaded, use the macro with-eval-after-load:
This macro arranges to evaluate body at the end of loading the file library, each time library is loaded. If library is already loaded, it evaluates body right away.
You don't need to give a directory or extension in the file name library. Normally, you just give a bare file name, like this:
(with-eval-after-load "edebug" (def-edebug-spec c-point t))To restrict which files can trigger the evaluation, include a directory or an extension or both in library. Only a file whose absolute true name (i.e., the name with all symbolic links chased out) matches all the given name components will match. In the following example, my_inst.elc or my_inst.elc.gz in some directory
..../foo/barwill trigger the evaluation, but not my_inst.el:(with-eval-after-load "foo/bar/my_inst.elc" ...)library can also be a feature (i.e., a symbol), in which case body is evaluated at the end of any file where
(providelibrary)is called.An error in body does not undo the load, but does prevent execution of the rest of body.
Normally, well-designed Lisp programs should not use
with-eval-after-load. If you need to examine and set the
variables defined in another library (those meant for outside use),
you can do it immediately—there is no need to wait until the library
is loaded. If you need to call functions defined by that library, you
should load the library, preferably with require (see Named Features).
A dynamic Emacs module is a shared library that provides additional functionality for use in Emacs Lisp programs, just like a package written in Emacs Lisp would.
Functions that load Emacs Lisp packages can also load dynamic modules. They recognize dynamic modules by looking at their file-name extension, a.k.a. “suffix”. This suffix is platform-dependent.
This variable holds the system-dependent value of the file-name extension of the module files. Its value is .so on Posix hosts and .dll on MS-Windows.
Every dynamic module should export a C-callable function named
emacs_module_init, which Emacs will call as part of the call to
load or require which loads the module. It should also
export a symbol named plugin_is_GPL_compatible to indicate that
its code is released under the GPL or compatible license; Emacs will
refuse to load modules that don't export such a symbol.
If a module needs to call Emacs functions, it should do so through the API defined and documented in the header file emacs-module.h that is part of the Emacs distribution.
Modules can create user-ptr Lisp objects that embed pointers to
C struct's defined by the module. This is useful for keeping around
complex data structures created by a module, to be passed back to the
module's functions. User-ptr objects can also have associated
finalizers – functions to be run when the object is GC'ed; this
is useful for freeing any resources allocated for the underlying data
structure, such as memory, open file descriptors, etc.
Loadable modules in Emacs are enabled by using the --with-modules option at configure time.
Emacs Lisp has a compiler that translates functions written in Lisp into a special representation called byte-code that can be executed more efficiently. The compiler replaces Lisp function definitions with byte-code. When a byte-code function is called, its definition is evaluated by the byte-code interpreter.
Because the byte-compiled code is evaluated by the byte-code interpreter, instead of being executed directly by the machine's hardware (as true compiled code is), byte-code is completely transportable from machine to machine without recompilation. It is not, however, as fast as true compiled code.
In general, any version of Emacs can run byte-compiled code produced by recent earlier versions of Emacs, but the reverse is not true.
If you do not want a Lisp file to be compiled, ever, put a file-local
variable binding for no-byte-compile into it, like this:
;; -*-no-byte-compile: t; -*-
A byte-compiled function is not as efficient as a primitive function written in C, but runs much faster than the version written in Lisp. Here is an example:
(defun silly-loop (n)
"Return the time, in seconds, to run N iterations of a loop."
(let ((t1 (float-time)))
(while (> (setq n (1- n)) 0))
(- (float-time) t1)))
=> silly-loop
(silly-loop 50000000)
=> 10.235304117202759
(byte-compile 'silly-loop)
=> [Compiled code not shown]
(silly-loop 50000000)
=> 3.705854892730713
In this example, the interpreted code required 10 seconds to run, whereas the byte-compiled code required less than 4 seconds. These results are representative, but actual results may vary.
You can byte-compile an individual function or macro definition with
the byte-compile function. You can compile a whole file with
byte-compile-file, or several files with
byte-recompile-directory or batch-byte-compile.
Sometimes, the byte compiler produces warning and/or error messages (see Compiler Errors, for details). These messages are recorded in a buffer called *Compile-Log*, which uses Compilation mode. See Compilation Mode.
Be careful when writing macro calls in files that you intend to
byte-compile. Since macro calls are expanded when they are compiled,
the macros need to be loaded into Emacs or the byte compiler will not
do the right thing. The usual way to handle this is with
require forms which specify the files containing the needed
macro definitions (see Named Features). Normally, the
byte compiler does not evaluate the code that it is compiling, but it
handles require forms specially, by loading the specified
libraries. To avoid loading the macro definition files when someone
runs the compiled program, write eval-when-compile
around the require calls (see Eval During Compile). For
more details, See Compiling Macros.
Inline (defsubst) functions are less troublesome; if you
compile a call to such a function before its definition is known, the
call will still work right, it will just run slower.
This function byte-compiles the function definition of symbol, replacing the previous definition with the compiled one. The function definition of symbol must be the actual code for the function;
byte-compiledoes not handle function indirection. The return value is the byte-code function object which is the compiled definition of symbol (see Byte-Code Objects).(defun factorial (integer) "Compute factorial of INTEGER." (if (= 1 integer) 1 (* integer (factorial (1- integer))))) => factorial (byte-compile 'factorial) => #[(integer) "^H\301U\203^H^@\301\207\302^H\303^HS!\"\207" [integer 1 * factorial] 4 "Compute factorial of INTEGER."]If symbol's definition is a byte-code function object,
byte-compiledoes nothing and returnsnil. It does not compile the symbol's definition again, since the original (non-compiled) code has already been replaced in the symbol's function cell by the byte-compiled code.The argument to
byte-compilecan also be alambdaexpression. In that case, the function returns the corresponding compiled code but does not store it anywhere.
This command reads the defun containing point, compiles it, and evaluates the result. If you use this on a defun that is actually a function definition, the effect is to install a compiled version of that function.
compile-defunnormally displays the result of evaluation in the echo area, but if arg is non-nil, it inserts the result in the current buffer after the form it compiled.
This function compiles a file of Lisp code named filename into a file of byte-code. The output file's name is made by changing the `.el' suffix into `.elc'; if filename does not end in `.el', it adds `.elc' to the end of filename.
Compilation works by reading the input file one form at a time. If it is a definition of a function or macro, the compiled function or macro definition is written out. Other forms are batched together, then each batch is compiled, and written so that its compiled code will be executed when the file is read. All comments are discarded when the input file is read.
This command returns
tif there were no errors andnilotherwise. When called interactively, it prompts for the file name.If load is non-
nil, this command loads the compiled file after compiling it. Interactively, load is the prefix argument.$ ls -l push* -rw-r--r-- 1 lewis lewis 791 Oct 5 20:31 push.el (byte-compile-file "~/emacs/push.el") => t $ ls -l push* -rw-r--r-- 1 lewis lewis 791 Oct 5 20:31 push.el -rw-rw-rw- 1 lewis lewis 638 Oct 8 20:25 push.elc
This command recompiles every `.el' file in directory (or its subdirectories) that needs recompilation. A file needs recompilation if a `.elc' file exists but is older than the `.el' file.
When a `.el' file has no corresponding `.elc' file, flag says what to do. If it is
nil, this command ignores these files. If flag is 0, it compiles them. If it is neithernilnor 0, it asks the user whether to compile each such file, and asks about each subdirectory as well.Interactively,
byte-recompile-directoryprompts for directory and flag is the prefix argument.If force is non-
nil, this command recompiles every `.el' file that has a `.elc' file.The returned value is unpredictable.
This function runs
byte-compile-fileon files specified on the command line. This function must be used only in a batch execution of Emacs, as it kills Emacs on completion. An error in one file does not prevent processing of subsequent files, but no output file will be generated for it, and the Emacs process will terminate with a nonzero status code.If noforce is non-
nil, this function does not recompile files that have an up-to-date `.elc' file.$ emacs -batch -f batch-byte-compile *.el
When Emacs loads functions and variables from a byte-compiled file, it normally does not load their documentation strings into memory. Each documentation string is dynamically loaded from the byte-compiled file only when needed. This saves memory, and speeds up loading by skipping the processing of the documentation strings.
This feature has a drawback: if you delete, move, or alter the compiled file (such as by compiling a new version), Emacs may no longer be able to access the documentation string of previously-loaded functions or variables. Such a problem normally only occurs if you build Emacs yourself, and happen to edit and/or recompile the Lisp source files. To solve it, just reload each file after recompilation.
Dynamic loading of documentation strings from byte-compiled files is
determined, at compile time, for each byte-compiled file. It can be
disabled via the option byte-compile-dynamic-docstrings.
If this is non-
nil, the byte compiler generates compiled files that are set up for dynamic loading of documentation strings.To disable the dynamic loading feature for a specific file, set this option to
nilin its header line (see Local Variables in Files), like this:-*-byte-compile-dynamic-docstrings: nil;-*-This is useful mainly if you expect to change the file, and you want Emacs sessions that have already loaded it to keep working when the file changes.
Internally, the dynamic loading of documentation strings is accomplished by writing compiled files with a special Lisp reader construct, `#@count'. This construct skips the next count characters. It also uses the `#$' construct, which stands for the name of this file, as a string. Do not use these constructs in Lisp source files; they are not designed to be clear to humans reading the file.
When you compile a file, you can optionally enable the dynamic function loading feature (also known as lazy loading). With dynamic function loading, loading the file doesn't fully read the function definitions in the file. Instead, each function definition contains a place-holder which refers to the file. The first time each function is called, it reads the full definition from the file, to replace the place-holder.
The advantage of dynamic function loading is that loading the file becomes much faster. This is a good thing for a file which contains many separate user-callable functions, if using one of them does not imply you will probably also use the rest. A specialized mode which provides many keyboard commands often has that usage pattern: a user may invoke the mode, but use only a few of the commands it provides.
The dynamic loading feature has certain disadvantages:
These problems will never happen in normal circumstances with installed Emacs files. But they are quite likely to happen with Lisp files that you are changing. The easiest way to prevent these problems is to reload the new compiled file immediately after each recompilation.
The byte compiler uses the dynamic function loading feature if the
variable byte-compile-dynamic is non-nil at compilation
time. Do not set this variable globally, since dynamic loading is
desirable only for certain files. Instead, enable the feature for
specific source files with file-local variable bindings. For example,
you could do it by writing this text in the source file's first line:
-*-byte-compile-dynamic: t;-*-
If this is non-
nil, the byte compiler generates compiled files that are set up for dynamic function loading.
If function is a byte-code function object, this immediately finishes loading the byte code of function from its byte-compiled file, if it is not fully loaded already. Otherwise, it does nothing. It always returns function.
These features permit you to write code to be evaluated during compilation of a program.
This form marks body to be evaluated both when you compile the containing code and when you run it (whether compiled or not).
You can get a similar result by putting body in a separate file and referring to that file with
require. That method is preferable when body is large. Effectivelyrequireis automaticallyeval-and-compile, the package is loaded both when compiling and executing.
autoloadis also effectivelyeval-and-compiletoo. It's recognized when compiling, so uses of such a function don't produce “not known to be defined” warnings.Most uses of
eval-and-compileare fairly sophisticated.If a macro has a helper function to build its result, and that macro is used both locally and outside the package, then
eval-and-compileshould be used to get the helper both when compiling and then later when running.If functions are defined programmatically (with
fsetsay), theneval-and-compilecan be used to have that done at compile-time as well as run-time, so calls to those functions are checked (and warnings about “not known to be defined” suppressed).
This form marks body to be evaluated at compile time but not when the compiled program is loaded. The result of evaluation by the compiler becomes a constant which appears in the compiled program. If you load the source file, rather than compiling it, body is evaluated normally.
If you have a constant that needs some calculation to produce,
eval-when-compilecan do that at compile-time. For example,(defvar my-regexp (eval-when-compile (regexp-opt '("aaa" "aba" "abb"))))If you're using another package, but only need macros from it (the byte compiler will expand those), then
eval-when-compilecan be used to load it for compiling, but not executing. For example,(eval-when-compile (require 'my-macro-package))The same sort of thing goes for macros and
defsubstfunctions defined locally and only for use within the file. They are needed for compiling the file, but in most cases they are not needed for execution of the compiled file. For example,(eval-when-compile (unless (fboundp 'some-new-thing) (defmacro 'some-new-thing () (compatibility code))))This is often good for code that's only a fallback for compatibility with other versions of Emacs.
Common Lisp Note: At top level,
eval-when-compileis analogous to the Common Lisp idiom(eval-when (compile eval) ...). Elsewhere, the Common Lisp `#.' reader macro (but not when interpreting) is closer to whateval-when-compiledoes.
Error and warning messages from byte compilation are printed in a buffer named *Compile-Log*. These messages include file names and line numbers identifying the location of the problem. The usual Emacs commands for operating on compiler output can be used on these messages.
When an error is due to invalid syntax in the program, the byte compiler might get confused about the errors' exact location. One way to investigate is to switch to the buffer *Compiler Input*. (This buffer name starts with a space, so it does not show up in the Buffer Menu.) This buffer contains the program being compiled, and point shows how far the byte compiler was able to read; the cause of the error might be nearby. See Syntax Errors, for some tips for locating syntax errors.
A common type of warning issued by the byte compiler is for functions and variables that were used but not defined. Such warnings report the line number for the end of the file, not the locations where the missing functions or variables were used; to find these, you must search the file manually.
If you are sure that a warning message about a missing function or variable is unjustified, there are several ways to suppress it:
fboundp test, like
this:
(if (fboundp 'func) ...(func ...)...)
The call to func must be in the then-form of the
if, and func must appear quoted in the call to
fboundp. (This feature operates for cond as well.)
boundp
test:
(if (boundp 'variable) ...variable...)
The reference to variable must be in the then-form of the
if, and variable must appear quoted in the call to
boundp.
declare-function. See Declaring Functions.
defvar with no initial value. (Note that this marks the
variable as special.) See Defining Variables.
You can also suppress any and all compiler warnings within a certain
expression using the construct with-no-warnings:
In execution, this is equivalent to
(prognbody...), but the compiler does not issue warnings for anything that occurs inside body.We recommend that you use this construct around the smallest possible piece of code, to avoid missing possible warnings other than one you intend to suppress.
Byte compiler warnings can be controlled more precisely by setting
the variable byte-compile-warnings. See its documentation
string for details.
Byte-compiled functions have a special data type: they are byte-code function objects. Whenever such an object appears as a function to be called, Emacs uses the byte-code interpreter to execute the byte-code.
Internally, a byte-code function object is much like a vector; its
elements can be accessed using aref. Its printed
representation is like that for a vector, with an additional `#'
before the opening `['. It must have at least four elements;
there is no maximum number, but only the first six elements have any
normal use. They are:
&rest, then bit 7 is set; otherwise it's
cleared.
If argdesc is a list, the arguments will be dynamically bound
before executing the byte code. If argdesc is an integer, the
arguments will be instead pushed onto the stack of the byte-code
interpreter, before executing the code.
nil. The value may
be a number or a list, in case the documentation string is stored in a
file. Use the function documentation to get the real
documentation string (see Accessing Documentation).
nil for a function that isn't interactive.
Here's an example of a byte-code function object, in printed
representation. It is the definition of the command
backward-sexp.
#[256
"\211\204^G^@\300\262^A\301^A[!\207"
[1 forward-sexp]
3
1793299
"^p"]
The primitive way to create a byte-code object is with
make-byte-code:
This function constructs and returns a byte-code function object with elements as its elements.
You should not try to come up with the elements for a byte-code function yourself, because if they are inconsistent, Emacs may crash when you call the function. Always leave it to the byte compiler to create these objects; it makes the elements consistent (we hope).
People do not write byte-code; that job is left to the byte compiler. But we provide a disassembler to satisfy a cat-like curiosity. The disassembler converts the byte-compiled code into human-readable form.
The byte-code interpreter is implemented as a simple stack machine. It pushes values onto a stack of its own, then pops them off to use them in calculations whose results are themselves pushed back on the stack. When a byte-code function returns, it pops a value off the stack and returns it as the value of the function.
In addition to the stack, byte-code functions can use, bind, and set ordinary Lisp variables, by transferring values between variables and the stack.
This command displays the disassembled code for object. In interactive use, or if buffer-or-name is
nilor omitted, the output goes in a buffer named *Disassemble*. If buffer-or-name is non-nil, it must be a buffer or the name of an existing buffer. Then the output goes there, at point, and point is left before the output.The argument object can be a function name, a lambda expression (see Lambda Expressions), or a byte-code object (see Byte-Code Objects). If it is a lambda expression,
disassemblecompiles it and disassembles the resulting compiled code.
Here are two examples of using the disassemble function. We
have added explanatory comments to help you relate the byte-code to the
Lisp source; these do not appear in the output of disassemble.
(defun factorial (integer)
"Compute factorial of an integer."
(if (= 1 integer) 1
(* integer (factorial (1- integer)))))
=> factorial
(factorial 4)
=> 24
(disassemble 'factorial)
-| byte-code for factorial:
doc: Compute factorial of an integer.
args: (integer)
0 varref integer ; Get the value of integer and
; push it onto the stack.
1 constant 1 ; Push 1 onto stack.
2 eqlsign ; Pop top two values off stack, compare
; them, and push result onto stack.
3 goto-if-nil 1 ; Pop and test top of stack;
; if nil, go to 1, else continue.
6 constant 1 ; Push 1 onto top of stack.
7 return ; Return the top element of the stack.
8:1 varref integer ; Push value of integer onto stack.
9 constant factorial ; Push factorial onto stack.
10 varref integer ; Push value of integer onto stack.
11 sub1 ; Pop integer, decrement value,
; push new value onto stack.
12 call 1 ; Call function factorial using first
; (i.e., top) stack element as argument;
; push returned value onto stack.
13 mult ; Pop top two values off stack, multiply
; them, and push result onto stack.
14 return ; Return the top element of the stack.
The silly-loop function is somewhat more complex:
(defun silly-loop (n)
"Return time before and after N iterations of a loop."
(let ((t1 (current-time-string)))
(while (> (setq n (1- n))
0))
(list t1 (current-time-string))))
=> silly-loop
(disassemble 'silly-loop)
-| byte-code for silly-loop:
doc: Return time before and after N iterations of a loop.
args: (n)
0 constant current-time-string ; Push current-time-string
; onto top of stack.
1 call 0 ; Call current-time-string with no
; argument, push result onto stack.
2 varbind t1 ; Pop stack and bind t1 to popped value.
3:1 varref n ; Get value of n from the environment
; and push the value on the stack.
4 sub1 ; Subtract 1 from top of stack.
5 dup ; Duplicate top of stack; i.e., copy the top
; of the stack and push copy onto stack.
6 varset n ; Pop the top of the stack,
; and bind n to the value.
;; (In effect, the sequence dup varset copies the top of the stack
;; into the value of n without popping it.)
7 constant 0 ; Push 0 onto stack.
8 gtr ; Pop top two values off stack,
; test if n is greater than 0
; and push result onto stack.
9 goto-if-not-nil 1 ; Goto 1 if n > 0
; (this continues the while loop)
; else continue.
12 varref t1 ; Push value of t1 onto stack.
13 constant current-time-string ; Push current-time-string
; onto the top of the stack.
14 call 0 ; Call current-time-string again.
15 unbind 1 ; Unbind t1 in local environment.
16 list2 ; Pop top two elements off stack, create a
; list of them, and push it onto stack.
17 return ; Return value of the top of stack.
There are several ways to find and investigate problems in an Emacs Lisp program.
Other useful tools for debugging input and output problems are the
dribble file (see Terminal Input) and the open-termscript
function (see Terminal Output).
The ordinary Lisp debugger provides the ability to suspend evaluation of a form. While evaluation is suspended (a state that is commonly known as a break), you may examine the run time stack, examine the values of local or global variables, or change those values. Since a break is a recursive edit, all the usual editing facilities of Emacs are available; you can even run programs that will enter the debugger recursively. See Recursive Editing.
The most important time to enter the debugger is when a Lisp error happens. This allows you to investigate the immediate causes of the error.
However, entry to the debugger is not a normal consequence of an
error. Many commands signal Lisp errors when invoked inappropriately,
and during ordinary editing it would be very inconvenient to enter the
debugger each time this happens. So if you want errors to enter the
debugger, set the variable debug-on-error to non-nil.
(The command toggle-debug-on-error provides an easy way to do
this.)
This variable determines whether the debugger is called when an error is signaled and not handled. If
debug-on-errorist, all kinds of errors call the debugger, except those listed indebug-ignored-errors(see below). If it isnil, none call the debugger.The value can also be a list of error conditions (see Signaling Errors). Then the debugger is called only for error conditions in this list (except those also listed in
debug-ignored-errors). For example, if you setdebug-on-errorto the list(void-variable), the debugger is only called for errors about a variable that has no value.Note that
eval-expression-debug-on-erroroverrides this variable in some cases; see below.When this variable is non-
nil, Emacs does not create an error handler around process filter functions and sentinels. Therefore, errors in these functions also invoke the debugger. See Processes.
This variable specifies errors which should not enter the debugger, regardless of the value of
debug-on-error. Its value is a list of error condition symbols and/or regular expressions. If the error has any of those condition symbols, or if the error message matches any of the regular expressions, then that error does not enter the debugger.The normal value of this variable includes
user-error, as well as several errors that happen often during editing but rarely result from bugs in Lisp programs. However, “rarely” is not “never”; if your program fails with an error that matches this list, you may try changing this list to debug the error. The easiest way is usually to setdebug-ignored-errorstonil.
If this variable has a non-
nilvalue (the default), running the commandeval-expressioncausesdebug-on-errorto be temporarily bound to tot. See Evaluating Emacs-Lisp Expressions.If
eval-expression-debug-on-errorisnil, then the value ofdebug-on-erroris not changed duringeval-expression.
Normally, errors caught by
condition-casenever invoke the debugger. Thecondition-casegets a chance to handle the error before the debugger gets a chance.If you change
debug-on-signalto a non-nilvalue, the debugger gets the first chance at every error, regardless of the presence ofcondition-case. (To invoke the debugger, the error must still fulfill the criteria specified bydebug-on-erroranddebug-ignored-errors.)Warning: Setting this variable to non-
nilmay have annoying effects. Various parts of Emacs catch errors in the normal course of affairs, and you may not even realize that errors happen there. If you need to debug code wrapped incondition-case, consider usingcondition-case-unless-debug(see Handling Errors).
If you set
debug-on-eventto a special event (see Special Events), Emacs will try to enter the debugger as soon as it receives this event, bypassingspecial-event-map. At present, the only supported values correspond to the signalsSIGUSR1andSIGUSR2(this is the default). This can be helpful wheninhibit-quitis set and Emacs is not otherwise responding.
If you set
debug-on-messageto a regular expression, Emacs will enter the debugger if it displays a matching message in the echo area. For example, this can be useful when trying to find the cause of a particular message.
To debug an error that happens during loading of the init
file, use the option `--debug-init'. This binds
debug-on-error to t while loading the init file, and
bypasses the condition-case which normally catches errors in the
init file.
When a program loops infinitely and fails to return, your first problem is to stop the loop. On most operating systems, you can do this with C-g, which causes a quit. See Quitting.
Ordinary quitting gives no information about why the program was
looping. To get more information, you can set the variable
debug-on-quit to non-nil. Once you have the debugger
running in the middle of the infinite loop, you can proceed from the
debugger using the stepping commands. If you step through the entire
loop, you may get enough information to solve the problem.
Quitting with C-g is not considered an error, and
debug-on-error has no effect on the handling of C-g.
Likewise, debug-on-quit has no effect on errors.
This variable determines whether the debugger is called when
quitis signaled and not handled. Ifdebug-on-quitis non-nil, then the debugger is called whenever you quit (that is, type C-g). Ifdebug-on-quitisnil(the default), then the debugger is not called when you quit.
To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.
This function requests function-name to invoke the debugger each time it is called.
Any function or macro defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. If the function is a command, it will enter the debugger when called from Lisp and when called interactively (after the reading of the arguments). You can also set debug-on-entry for primitive functions (i.e., those written in C) this way, but it only takes effect when the primitive is called from Lisp code. Debug-on-entry is not allowed for special forms.
When
debug-on-entryis called interactively, it prompts for function-name in the minibuffer. If the function is already set up to invoke the debugger on entry,debug-on-entrydoes nothing.debug-on-entryalways returns function-name.Here's an example to illustrate use of this function:
(defun fact (n) (if (zerop n) 1 (* n (fact (1- n))))) => fact (debug-on-entry 'fact) => fact (fact 3) ------ Buffer: *Backtrace* ------ Debugger entered--entering a function: * fact(3) eval((fact 3)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ------ Buffer: *Backtrace* ------
This function undoes the effect of
debug-on-entryon function-name. When called interactively, it prompts for function-name in the minibuffer. If function-name is omitted ornil, it cancels break-on-entry for all functions. Callingcancel-debug-on-entrydoes nothing to a function which is not currently set up to break on entry.
You can cause the debugger to be called at a certain point in your
program by writing the expression (debug) at that point. To do
this, visit the source file, insert the text `(debug)' at the
proper place, and type C-M-x (eval-defun, a Lisp mode key
binding). Warning: if you do this for temporary debugging
purposes, be sure to undo this insertion before you save the file!
The place where you insert `(debug)' must be a place where an
additional form can be evaluated and its value ignored. (If the value
of (debug) isn't ignored, it will alter the execution of the
program!) The most common suitable places are inside a progn or
an implicit progn (see Sequencing).
If you don't know exactly where in the source code you want to put
the debug statement, but you want to display a backtrace when a
certain message is displayed, you can set debug-on-message to a
regular expression matching the desired message.
When the debugger is entered, it displays the previously selected buffer in one window and a buffer named *Backtrace* in another window. The backtrace buffer contains one line for each level of Lisp function execution currently going on. At the beginning of this buffer is a message describing the reason that the debugger was invoked (such as the error message and associated data, if it was invoked due to an error).
The backtrace buffer is read-only and uses a special major mode,
Debugger mode, in which letters are defined as debugger commands. The
usual Emacs editing commands are available; thus, you can switch windows
to examine the buffer that was being edited at the time of the error,
switch buffers, visit files, or do any other sort of editing. However,
the debugger is a recursive editing level (see Recursive Editing)
and it is wise to go back to the backtrace buffer and exit the debugger
(with the q command) when you are finished with it. Exiting
the debugger gets out of the recursive edit and buries the backtrace
buffer. (You can customize what the q command does with the
backtrace buffer by setting the variable debugger-bury-or-kill.
For example, set it to kill if you prefer to kill the buffer
rather than bury it. Consult the variable's documentation for more
possibilities.)
When the debugger has been entered, the debug-on-error
variable is temporarily set according to
eval-expression-debug-on-error. If the latter variable is
non-nil, debug-on-error will temporarily be set to
t. This means that any further errors that occur while doing a
debugging session will (by default) trigger another backtrace. If
this is not what you want, you can either set
eval-expression-debug-on-error to nil, or set
debug-on-error to nil in debugger-mode-hook.
The backtrace buffer shows you the functions that are executing and their argument values. It also allows you to specify a stack frame by moving point to the line describing that frame. (A stack frame is the place where the Lisp interpreter records information about a particular invocation of a function.) The frame whose line point is on is considered the current frame. Some of the debugger commands operate on the current frame. If a line starts with a star, that means that exiting that frame will call the debugger again. This is useful for examining the return value of a function.
If a function name is underlined, that means the debugger knows where its source code is located. You can click with the mouse on that name, or move to it and type <RET>, to visit the source code.
The debugger itself must be run byte-compiled, since it makes assumptions about how many stack frames are used for the debugger itself. These assumptions are false if the debugger is running interpreted.
The debugger buffer (in Debugger mode) provides special commands in addition to the usual Emacs commands. The most important use of debugger commands is for stepping through code, so that you can see how control flows. The debugger can step through the control structures of an interpreted function, but cannot do so in a byte-compiled function. If you would like to step through a byte-compiled function, replace it with an interpreted definition of the same function. (To do this, visit the source for the function and type C-M-x on its definition.) You cannot use the Lisp debugger to step through a primitive function.
Here is a list of Debugger mode commands:
The stack frame made for the function call which enters the debugger in
this way will be flagged automatically so that the debugger will be
called again when the frame is exited. You can use the u command
to cancel this flag.
debug-on-entry.
If the debugger was entered due to a C-g but you really want
to quit, and not debug, use the q command.
The r command is useful when the debugger was invoked due to exit
from a Lisp call frame (as requested with b or by entering the
frame with d); then the value specified in the r command is
used as the value of that frame. It is also useful if you call
debug and use its return value. Otherwise, r has the same
effect as c, and the specified return value does not matter.
You can't use r when the debugger was entered due to an error.
debug-on-entry.
Here we describe in full detail the function debug that is used
to invoke the debugger.
This function enters the debugger. It switches buffers to a buffer named *Backtrace* (or *Backtrace*<2> if it is the second recursive entry to the debugger, etc.), and fills it with information about the stack of Lisp function calls. It then enters a recursive edit, showing the backtrace buffer in Debugger mode.
The Debugger mode c, d, j, and r commands exit the recursive edit; then
debugswitches back to the previous buffer and returns to whatever calleddebug. This is the only way the functiondebugcan return to its caller.The use of the debugger-args is that
debugdisplays the rest of its arguments at the top of the *Backtrace* buffer, so that the user can see them. Except as described below, this is the only way these arguments are used.However, certain values for first argument to
debughave a special significance. (Normally, these values are used only by the internals of Emacs, and not by programmers callingdebug.) Here is a table of these special values:
lambda- A first argument of
lambdameansdebugwas called because of entry to a function whendebug-on-next-callwas non-nil. The debugger displays `Debugger entered--entering a function:' as a line of text at the top of the buffer.
debugdebugas first argument meansdebugwas called because of entry to a function that was set to debug on entry. The debugger displays the string `Debugger entered--entering a function:', just as in thelambdacase. It also marks the stack frame for that function so that it will invoke the debugger when exited.
t- When the first argument is
t, this indicates a call todebugdue to evaluation of a function call form whendebug-on-next-callis non-nil. The debugger displays `Debugger entered--beginning evaluation of function call form:' as the top line in the buffer.
exit- When the first argument is
exit, it indicates the exit of a stack frame previously marked to invoke the debugger on exit. The second argument given todebugin this case is the value being returned from the frame. The debugger displays `Debugger entered--returning value:' in the top line of the buffer, followed by the value being returned.
error- When the first argument is
error, the debugger indicates that it is being entered because an error orquitwas signaled and not handled, by displaying `Debugger entered--Lisp error:' followed by the error signaled and any arguments tosignal. For example,(let ((debug-on-error t)) (/ 1 0)) ------ Buffer: *Backtrace* ------ Debugger entered--Lisp error: (arith-error) /(1 0) ... ------ Buffer: *Backtrace* ------If an error was signaled, presumably the variable
debug-on-erroris non-nil. Ifquitwas signaled, then presumably the variabledebug-on-quitis non-nil.nil- Use
nilas the first of the debugger-args when you want to enter the debugger explicitly. The rest of the debugger-args are printed on the top line of the buffer. You can use this feature to display messages—for example, to remind yourself of the conditions under whichdebugis called.
This section describes functions and variables used internally by the debugger.
The value of this variable is the function to call to invoke the debugger. Its value must be a function of any number of arguments, or, more typically, the name of a function. This function should invoke some kind of debugger. The default value of the variable is
debug.The first argument that Lisp hands to the function indicates why it was called. The convention for arguments is detailed in the description of
debug(see Invoking the Debugger).
This function prints a trace of Lisp function calls currently active. This is the function used by
debugto fill up the *Backtrace* buffer. It is written in C, since it must have access to the stack to determine which function calls are active. The return value is alwaysnil.In the following example, a Lisp expression calls
backtraceexplicitly. This prints the backtrace to the streamstandard-output, which, in this case, is the buffer `backtrace-output'.Each line of the backtrace represents one function call. The line shows the values of the function's arguments if they are all known; if they are still being computed, the line says so. The arguments of special forms are elided.
(with-output-to-temp-buffer "backtrace-output" (let ((var 1)) (save-excursion (setq var (eval '(progn (1+ var) (list 'testing (backtrace)))))))) => (testing nil) ----------- Buffer: backtrace-output ------------ backtrace() (list ...computing arguments...) (progn ...) eval((progn (1+ var) (list (quote testing) (backtrace)))) (setq ...) (save-excursion ...) (let ...) (with-output-to-temp-buffer ...) eval((with-output-to-temp-buffer ...)) eval-last-sexp-1(nil) eval-last-sexp(nil) call-interactively(eval-last-sexp) ----------- Buffer: backtrace-output ------------
If this variable is non-
nil, it says to call the debugger before the nexteval,applyorfuncall. Entering the debugger setsdebug-on-next-calltonil.The d command in the debugger works by setting this variable.
This function sets the debug-on-exit flag of the stack frame level levels down the stack, giving it the value flag. If flag is non-
nil, this will cause the debugger to be entered when that frame later exits. Even a nonlocal exit through that frame will enter the debugger.This function is used only by the debugger.
This variable records the debugging status of the current interactive command. Each time a command is called interactively, this variable is bound to
nil. The debugger can set this variable to leave information for future debugger invocations during the same command invocation.The advantage of using this variable rather than an ordinary global variable is that the data will never carry over to a subsequent command invocation.
The function
backtrace-frameis intended for use in Lisp debuggers. It returns information about what computation is happening in the stack frame frame-number levels down.If that frame has not evaluated the arguments yet, or is a special form, the value is
(nilfunction arg-forms...).If that frame has evaluated its arguments and called its function already, the return value is
(tfunction arg-values...).In the return value, function is whatever was supplied as the car of the evaluated list, or a
lambdaexpression in the case of a macro call. If the function has a&restargument, that is represented as the tail of the list arg-values.If frame-number is out of range,
backtrace-framereturnsnil.
Edebug is a source-level debugger for Emacs Lisp programs, with which you can:
The first three sections below should tell you enough about Edebug to start using it.
To debug a Lisp program with Edebug, you must first instrument
the Lisp code that you want to debug. A simple way to do this is to
first move point into the definition of a function or macro and then do
C-u C-M-x (eval-defun with a prefix argument). See
Instrumenting, for alternative ways to instrument code.
Once a function is instrumented, any call to the function activates Edebug. Depending on which Edebug execution mode you have selected, activating Edebug may stop execution and let you step through the function, or it may update the display and continue execution while checking for debugging commands. The default execution mode is step, which stops execution. See Edebug Execution Modes.
Within Edebug, you normally view an Emacs buffer showing the source of the Lisp code you are debugging. This is referred to as the source code buffer, and it is temporarily read-only.
An arrow in the left fringe indicates the line where the function is executing. Point initially shows where within the line the function is executing, but this ceases to be true if you move point yourself.
If you instrument the definition of fac (shown below) and then
execute (fac 3), here is what you would normally see. Point is
at the open-parenthesis before if.
(defun fac (n)
=>-!-(if (< 0 n)
(* n (fac (1- n)))
1))
The places within a function where Edebug can stop execution are called
stop points. These occur both before and after each subexpression
that is a list, and also after each variable reference.
Here we use periods to show the stop points in the function
fac:
(defun fac (n)
.(if .(< 0 n.).
.(* n. .(fac .(1- n.).).).
1).)
The special commands of Edebug are available in the source code buffer
in addition to the commands of Emacs Lisp mode. For example, you can
type the Edebug command <SPC> to execute until the next stop point.
If you type <SPC> once after entry to fac, here is the
display you will see:
(defun fac (n)
=>(if -!-(< 0 n)
(* n (fac (1- n)))
1))
When Edebug stops execution after an expression, it displays the expression's value in the echo area.
Other frequently used commands are b to set a breakpoint at a stop point, g to execute until a breakpoint is reached, and q to exit Edebug and return to the top-level command loop. Type ? to display a list of all Edebug commands.
In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places.
When you invoke command C-M-x (eval-defun) with a
prefix argument on a function definition, it instruments the
definition before evaluating it. (This does not modify the source
code itself.) If the variable edebug-all-defs is
non-nil, that inverts the meaning of the prefix argument: in
this case, C-M-x instruments the definition unless it has
a prefix argument. The default value of edebug-all-defs is
nil. The command M-x edebug-all-defs toggles the value
of the variable edebug-all-defs.
If edebug-all-defs is non-nil, then the commands
eval-region, eval-current-buffer, and eval-buffer
also instrument any definitions they evaluate. Similarly,
edebug-all-forms controls whether eval-region should
instrument any form, even non-defining forms. This doesn't apply
to loading or evaluations in the minibuffer. The command M-x
edebug-all-forms toggles this option.
Another command, M-x edebug-eval-top-level-form, is available to
instrument any top-level form regardless of the values of
edebug-all-defs and edebug-all-forms.
edebug-defun is an alias for edebug-eval-top-level-form.
While Edebug is active, the command I
(edebug-instrument-callee) instruments the definition of the
function or macro called by the list form after point, if it is not already
instrumented. This is possible only if Edebug knows where to find the
source for that function; for this reason, after loading Edebug,
eval-region records the position of every definition it
evaluates, even if not instrumenting it. See also the i command
(see Jumping), which steps into the call after instrumenting the
function.
Edebug knows how to instrument all the standard special forms,
interactive forms with an expression argument, anonymous lambda
expressions, and other defining forms. However, Edebug cannot determine
on its own what a user-defined macro will do with the arguments of a
macro call, so you must provide that information using Edebug
specifications; for details, see Edebug and Macros.
When Edebug is about to instrument code for the first time in a
session, it runs the hook edebug-setup-hook, then sets it to
nil. You can use this to load Edebug specifications
associated with a package you are using, but only when you use Edebug.
To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument. There are two ways of
evaluating forms that never instrument them: from a file with
load, and from the minibuffer with eval-expression
(M-:).
If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an invalid-read-syntax error.
See Edebug Eval, for other evaluation functions available inside of Edebug.
Edebug supports several execution modes for running the program you are debugging. We call these alternatives Edebug execution modes; do not confuse them with major or minor modes. The current Edebug execution mode determines how far Edebug continues execution before stopping—whether it stops at each stop point, or continues to the next breakpoint, for example—and how much Edebug displays the progress of the evaluation before it stops.
Normally, you specify the Edebug execution mode by typing a command to continue the program in a certain mode. Here is a table of these commands; all except for S resume execution of the program, at least for a certain distance.
edebug-stop).
edebug-step-mode).
edebug-next-mode). Also see edebug-forward-sexp in
Jumping.
edebug-trace-mode).
edebug-Trace-fast-mode).
edebug-go-mode). See Breakpoints.
edebug-continue-mode).
edebug-Continue-fast-mode).
edebug-Go-nonstop-mode). You
can still stop the program by typing S, or any editing command.
In general, the execution modes earlier in the above list run the program more slowly or stop sooner than the modes later in the list.
When you enter a new Edebug level, Edebug will normally stop at the
first instrumented function it encounters. If you prefer to stop only
at a break point, or not at all (for example, when gathering coverage
data), change the value of edebug-initial-mode from its default
step to go, or Go-nonstop, or one of its other
values (see Edebug Options). You can do this readily with
C-x C-a C-m (edebug-set-initial-mode):
This command, bound to C-x C-a C-m, sets
edebug-initial-mode. It prompts you for a key to indicate the mode. You should enter one of the eight keys listed above, which sets the corresponding mode.
Note that you may reenter the same Edebug level several times if, for example, an instrumented function is called several times from one command.
While executing or tracing, you can interrupt the execution by typing any Edebug command. Edebug stops the program at the next stop point and then executes the command you typed. For example, typing t during execution switches to trace mode at the next stop point. You can use S to stop execution without doing anything else.
If your function happens to read input, a character you type intending to interrupt execution may be read by the function instead. You can avoid such unintended results by paying attention to when your program wants input.
Keyboard macros containing the commands in this section do not
completely work: exiting from Edebug, to resume the program, loses track
of the keyboard macro. This is not easy to fix. Also, defining or
executing a keyboard macro outside of Edebug does not affect commands
inside Edebug. This is usually an advantage. See also the
edebug-continue-kbd-macro option in Edebug Options.
This option specifies how many seconds to wait between execution steps in trace mode or continue mode. The default is 1 second.
The commands described in this section execute until they reach a specified location. All except i make a temporary breakpoint to establish the place to stop, then switch to go mode. Any other breakpoint reached before the intended stop point will also stop execution. See Breakpoints, for the details on breakpoints.
These commands may fail to work as expected in case of nonlocal exit, as that can bypass the temporary breakpoint where you expected the program to stop.
edebug-goto-here).
edebug-forward-sexp).
edebug-step-out).
edebug-step-in).
The h command proceeds to the stop point at or after the current location of point, using a temporary breakpoint.
The f command runs the program forward over one expression. More
precisely, it sets a temporary breakpoint at the position that
forward-sexp would reach, then executes in go mode so that
the program will stop at breakpoints.
With a prefix argument n, the temporary breakpoint is placed n sexps beyond point. If the containing list ends before n more elements, then the place to stop is after the containing expression.
You must check that the position forward-sexp finds is a place
that the program will really get to. In cond, for example,
this may not be true.
For flexibility, the f command does forward-sexp starting
at point, rather than at the stop point. If you want to execute one
expression from the current stop point, first type w
(edebug-where) to move point there, and then type f.
The o command continues out of an expression. It places a temporary breakpoint at the end of the sexp containing point. If the containing sexp is a function definition itself, o continues until just before the last sexp in the definition. If that is where you are now, it returns from the function and then stops. In other words, this command does not exit the currently executing function unless you are positioned after the last sexp.
The i command steps into the function or macro called by the list form after point, and stops at its first stop point. Note that the form need not be the one about to be evaluated. But if the form is a function call about to be evaluated, remember to use this command before any of the arguments are evaluated, since otherwise it will be too late.
The i command instruments the function or macro it's supposed to step into, if it isn't instrumented already. This is convenient, but keep in mind that the function or macro remains instrumented unless you explicitly arrange to deinstrument it.
Some miscellaneous Edebug commands are described here.
edebug-help).
abort-recursive-edit).
top-level). This
exits all recursive editing levels, including all levels of Edebug
activity. However, instrumented code protected with
unwind-protect or condition-case forms may resume
debugging.
edebug-top-level-nonstop).
edebug-previous-result).
edebug-backtrace).
You cannot use debugger commands in the backtrace buffer in Edebug as you would in the standard debugger.
The backtrace buffer is killed automatically when you continue execution.
You can invoke commands from Edebug that activate Edebug again recursively. Whenever Edebug is active, you can quit to the top level with q or abort one recursive edit level with C-]. You can display a backtrace of all the pending evaluations with d.
Edebug's step mode stops execution when the next stop point is reached. There are three other ways to stop Edebug execution once it has started: breakpoints, the global break condition, and source breakpoints.
While using Edebug, you can specify breakpoints in the program you are testing: these are places where execution should stop. You can set a breakpoint at any stop point, as defined in Using Edebug. For setting and unsetting breakpoints, the stop point that is affected is the first one at or after point in the source code buffer. Here are the Edebug commands for breakpoints:
edebug-set-breakpoint). If you use a prefix argument, the
breakpoint is temporary—it turns off the first time it stops the
program.
edebug-unset-breakpoint).
nil value
(edebug-set-conditional-breakpoint). With a prefix argument,
the breakpoint is temporary.
edebug-next-breakpoint).
While in Edebug, you can set a breakpoint with b and unset one with u. First move point to the Edebug stop point of your choice, then type b or u to set or unset a breakpoint there. Unsetting a breakpoint where none has been set has no effect.
Re-evaluating or reinstrumenting a definition removes all of its previous breakpoints.
A conditional breakpoint tests a condition each time the program
gets there. Any errors that occur as a result of evaluating the
condition are ignored, as if the result were nil. To set a
conditional breakpoint, use x, and specify the condition
expression in the minibuffer. Setting a conditional breakpoint at a
stop point that has a previously established conditional breakpoint puts
the previous condition expression in the minibuffer so you can edit it.
You can make a conditional or unconditional breakpoint temporary by using a prefix argument with the command to set the breakpoint. When a temporary breakpoint stops the program, it is automatically unset.
Edebug always stops or pauses at a breakpoint, except when the Edebug mode is Go-nonstop. In that mode, it ignores breakpoints entirely.
To find out where your breakpoints are, use the B command, which moves point to the next breakpoint following point, within the same function, or to the first breakpoint if there are no following breakpoints. This command does not continue execution—it just moves point in the buffer.
A global break condition stops execution when a specified
condition is satisfied, no matter where that may occur. Edebug
evaluates the global break condition at every stop point; if it
evaluates to a non-nil value, then execution stops or pauses
depending on the execution mode, as if a breakpoint had been hit. If
evaluating the condition gets an error, execution does not stop.
The condition expression is stored in
edebug-global-break-condition. You can specify a new expression
using the X command from the source code buffer while Edebug is
active, or using C-x X X from any buffer at any time, as long as
Edebug is loaded (edebug-set-global-break-condition).
The global break condition is the simplest way to find where in your
code some event occurs, but it makes code run much more slowly. So you
should reset the condition to nil when not using it.
All breakpoints in a definition are forgotten each time you
reinstrument it. If you wish to make a breakpoint that won't be
forgotten, you can write a source breakpoint, which is simply a
call to the function edebug in your source code. You can, of
course, make such a call conditional. For example, in the fac
function, you can insert the first line as shown below, to stop when the
argument reaches zero:
(defun fac (n)
(if (= n 0) (edebug))
(if (< 0 n)
(* n (fac (1- n)))
1))
When the fac definition is instrumented and the function is
called, the call to edebug acts as a breakpoint. Depending on
the execution mode, Edebug stops or pauses there.
If no instrumented code is being executed when edebug is called,
that function calls debug.
Emacs normally displays an error message when an error is signaled and
not handled with condition-case. While Edebug is active and
executing instrumented code, it normally responds to all unhandled
errors. You can customize this with the options edebug-on-error
and edebug-on-quit; see Edebug Options.
When Edebug responds to an error, it shows the last stop point encountered before the error. This may be the location of a call to a function which was not instrumented, and within which the error actually occurred. For an unbound variable error, the last known stop point might be quite distant from the offending variable reference. In that case, you might want to display a full backtrace (see Edebug Misc).
If you change debug-on-error or debug-on-quit while
Edebug is active, these changes will be forgotten when Edebug becomes
inactive. Furthermore, during Edebug's recursive edit, these variables
are bound to the values they had outside of Edebug.
These Edebug commands let you view aspects of the buffer and window status as they were before entry to Edebug. The outside window configuration is the collection of windows and contents that were in effect outside of Edebug.
edebug-view-outside). Type C-x X w to return to Edebug.
edebug-bounce-point), pausing for one second
before returning to Edebug. With a prefix argument n, pause for
n seconds instead.
edebug-where).
If you use this command in a different window displaying the same
buffer, that window will be used instead to display the current
definition in the future.
edebug-toggle-save-windows).
With a prefix argument, W only toggles saving and restoring of
the selected window. To specify a window that is not displaying the
source code buffer, you must use C-x X W from the global keymap.
You can view the outside window configuration with v or just bounce to the point in the current buffer with p, even if it is not normally displayed.
After moving point, you may wish to jump back to the stop point. You can do that with w from a source code buffer. You can jump back to the stop point in the source code buffer from any buffer using C-x X w.
Each time you use W to turn saving off, Edebug forgets the saved outside window configuration—so that even if you turn saving back on, the current window configuration remains unchanged when you next exit Edebug (by continuing the program). However, the automatic redisplay of *edebug* and *edebug-trace* may conflict with the buffers you wish to see unless you have enough windows open.
While within Edebug, you can evaluate expressions as if Edebug were not running. Edebug tries to be invisible to the expression's evaluation and printing. Evaluation of expressions that cause side effects will work as expected, except for changes to data that Edebug explicitly saves and restores. See The Outside Context, for details on this process.
edebug-eval-expression). That is, Edebug tries to minimize its
interference with the evaluation.
eval-expression).
edebug-eval-last-sexp).
Edebug supports evaluation of expressions containing references to
lexically bound symbols created by the following constructs in
cl.el: lexical-let, macrolet, and
symbol-macrolet.
You can use the evaluation list buffer, called *edebug*, to evaluate expressions interactively. You can also set up the evaluation list of expressions to be evaluated automatically each time Edebug updates the display.
edebug-visit-eval-list).
In the *edebug* buffer you can use the commands of Lisp Interaction mode (see Lisp Interaction) as well as these special commands:
edebug-eval-print-last-sexp).
edebug-eval-last-sexp).
edebug-update-eval-list).
edebug-delete-eval-item).
edebug-where).
You can evaluate expressions in the evaluation list window with C-j or C-x C-e, just as you would in *scratch*; but they are evaluated in the context outside of Edebug.
The expressions you enter interactively (and their results) are lost when you continue execution; but you can set up an evaluation list consisting of expressions to be evaluated each time execution stops.
To do this, write one or more evaluation list groups in the evaluation list buffer. An evaluation list group consists of one or more Lisp expressions. Groups are separated by comment lines.
The command C-c C-u (edebug-update-eval-list) rebuilds the
evaluation list, scanning the buffer and using the first expression of
each group. (The idea is that the second expression of the group is the
value previously computed and displayed.)
Each entry to Edebug redisplays the evaluation list by inserting each expression in the buffer, followed by its current value. It also inserts comment lines so that each expression becomes its own group. Thus, if you type C-c C-u again without changing the buffer text, the evaluation list is effectively unchanged.
If an error occurs during an evaluation from the evaluation list, the error message is displayed in a string as if it were the result. Therefore, expressions using variables that are not currently valid do not interrupt your debugging.
Here is an example of what the evaluation list window looks like after several expressions have been added to it:
(current-buffer)
#<buffer *scratch*>
;---------------------------------------------------------------
(selected-window)
#<window 16 on *scratch*>
;---------------------------------------------------------------
(point)
196
;---------------------------------------------------------------
bad-var
"Symbol's value as variable is void: bad-var"
;---------------------------------------------------------------
(recursion-depth)
0
;---------------------------------------------------------------
this-command
eval-last-sexp
;---------------------------------------------------------------
To delete a group, move point into it and type C-c C-d, or simply delete the text for the group and update the evaluation list with C-c C-u. To add a new expression to the evaluation list, insert the expression at a suitable place, insert a new comment line, then type C-c C-u. You need not insert dashes in the comment line—its contents don't matter.
After selecting *edebug*, you can return to the source code buffer with C-c C-w. The *edebug* buffer is killed when you continue execution, and recreated next time it is needed.
If an expression in your program produces a value containing circular list structure, you may get an error when Edebug attempts to print it.
One way to cope with circular structure is to set print-length
or print-level to truncate the printing. Edebug does this for
you; it binds print-length and print-level to the values
of the variables edebug-print-length and
edebug-print-level (so long as they have non-nil
values). See Output Variables.
If non-
nil, Edebug bindsprint-lengthto this value while printing results. The default value is50.
If non-
nil, Edebug bindsprint-levelto this value while printing results. The default value is50.
You can also print circular structures and structures that share
elements more informatively by binding print-circle
to a non-nil value.
Here is an example of code that creates a circular structure:
(setq a '(x y))
(setcar a a)
Custom printing prints this as `Result: #1=(#1# y)'. The `#1=' notation labels the structure that follows it with the label `1', and the `#1#' notation references the previously labeled structure. This notation is used for any shared elements of lists or vectors.
If non-
nil, Edebug bindsprint-circleto this value while printing results. The default value ist.
Other programs can also use custom printing; see cust-print.el for details.
Edebug can record an execution trace, storing it in a buffer named
*edebug-trace*. This is a log of function calls and returns,
showing the function names and their arguments and values. To enable
trace recording, set edebug-trace to a non-nil value.
Making a trace buffer is not the same thing as using trace execution mode (see Edebug Execution Modes).
When trace recording is enabled, each function entry and exit adds lines to the trace buffer. A function entry record consists of `::::{', followed by the function name and argument values. A function exit record consists of `::::}', followed by the function name and result of the function.
The number of `:'s in an entry shows its recursion depth. You can use the braces in the trace buffer to find the matching beginning or end of function calls.
You can customize trace recording for function entry and exit by
redefining the functions edebug-print-trace-before and
edebug-print-trace-after.
This macro requests additional trace information around the execution of the body forms. The argument string specifies text to put in the trace buffer, after the `{' or `}'. All the arguments are evaluated, and
edebug-tracingreturns the value of the last form in body.
This function inserts text in the trace buffer. It computes the text with
(apply 'formatformat-string format-args). It also appends a newline to separate entries.
edebug-tracing and edebug-trace insert lines in the
trace buffer whenever they are called, even if Edebug is not active.
Adding text to the trace buffer also scrolls its window to show the last
lines inserted.
Edebug provides rudimentary coverage testing and display of execution frequency.
Coverage testing works by comparing the result of each expression with the previous result; each form in the program is considered covered if it has returned two different values since you began testing coverage in the current Emacs session. Thus, to do coverage testing on your program, execute it under various conditions and note whether it behaves correctly; Edebug will tell you when you have tried enough different conditions that each form has returned two different values.
Coverage testing makes execution slower, so it is only done if
edebug-test-coverage is non-nil. Frequency counting is
performed for all executions of an instrumented function, even if the
execution mode is Go-nonstop, and regardless of whether coverage testing
is enabled.
Use C-x X = (edebug-display-freq-count) to display both
the coverage information and the frequency counts for a definition.
Just = (edebug-temp-display-freq-count) displays the same
information temporarily, only until you type another key.
This command displays the frequency count data for each line of the current definition.
It inserts frequency counts as comment lines after each line of code. You can undo all insertions with one
undocommand. The counts appear under the `(' before an expression or the `)' after an expression, or on the last character of a variable. To simplify the display, a count is not shown if it is equal to the count of an earlier expression on the same line.The character `=' following the count for an expression says that the expression has returned the same value each time it was evaluated. In other words, it is not yet covered for coverage testing purposes.
To clear the frequency count and coverage data for a definition, simply reinstrument it with
eval-defun.
For example, after evaluating (fac 5) with a source
breakpoint, and setting edebug-test-coverage to t, when
the breakpoint is reached, the frequency data looks like this:
(defun fac (n)
(if (= n 0) (edebug))
;#6 1 = =5
(if (< 0 n)
;#5 =
(* n (fac (1- n)))
;# 5 0
1))
;# 0
The comment lines show that fac was called 6 times. The
first if statement returned 5 times with the same result each
time; the same is true of the condition on the second if.
The recursive call of fac did not return at all.
Edebug tries to be transparent to the program you are debugging, but it does not succeed completely. Edebug also tries to be transparent when you evaluate expressions with e or with the evaluation list buffer, by temporarily restoring the outside context. This section explains precisely what context Edebug restores, and how Edebug fails to be completely transparent.
Whenever Edebug is entered, it needs to save and restore certain data before even deciding whether to make trace information or stop the program.
max-lisp-eval-depth and max-specpdl-size are both
increased to reduce Edebug's impact on the stack. You could, however,
still run out of stack space when using Edebug.
executing-kbd-macro is bound to nil
unless edebug-continue-kbd-macro is non-nil.
When Edebug needs to display something (e.g., in trace mode), it saves the current window configuration from outside Edebug (see Window Configurations). When you exit Edebug, it restores the previous window configuration.
Emacs redisplays only when it pauses. Usually, when you continue execution, the program re-enters Edebug at a breakpoint or after stepping, without pausing or reading input in between. In such cases, Emacs never gets a chance to redisplay the outside configuration. Consequently, what you see is the same window configuration as the last time Edebug was active, with no interruption.
Entry to Edebug for displaying something also saves and restores the following data (though some of them are deliberately not restored if an error or quit signal occurs).
edebug-save-windows is non-nil (see Edebug Options).
The window configuration is not restored on error or quit, but the
outside selected window is reselected even on error or quit in
case a save-excursion is active. If the value of
edebug-save-windows is a list, only the listed windows are saved
and restored.
The window start and horizontal scrolling of the source code buffer are not restored, however, so that the display remains coherent within Edebug.
edebug-save-displayed-buffer-points is non-nil.
overlay-arrow-position and
overlay-arrow-string are saved and restored, so you can safely
invoke Edebug from the recursive edit elsewhere in the same buffer.
cursor-in-echo-area is locally bound to nil so that
the cursor shows up in the window.
When Edebug is entered and actually reads commands from the user, it saves (and later restores) these additional data:
last-command, this-command,
last-command-event, last-input-event,
last-event-frame, last-nonmenu-event, and
track-mouse. Commands in Edebug do not affect these variables
outside of Edebug.
Executing commands within Edebug can change the key sequence that
would be returned by this-command-keys, and there is no way to
reset the key sequence from Lisp.
Edebug cannot save and restore the value of
unread-command-events. Entering Edebug while this variable has a
nontrivial value can interfere with execution of the program you are
debugging.
command-history. In rare cases this can alter execution.
standard-output and standard-input are bound to nil
by the recursive-edit, but Edebug temporarily restores them during
evaluations.
defining-kbd-macro is bound to
edebug-continue-kbd-macro.
To make Edebug properly instrument expressions that call macros, some extra care is needed. This subsection explains the details.
When Edebug instruments an expression that calls a Lisp macro, it needs additional information about the macro to do the job properly. This is because there is no a-priori way to tell which subexpressions of the macro call are forms to be evaluated. (Evaluation may occur explicitly in the macro body, or when the resulting expansion is evaluated, or any time later.)
Therefore, you must define an Edebug specification for each macro
that Edebug will encounter, to explain the format of calls to that
macro. To do this, add a debug declaration to the macro
definition. Here is a simple example that shows the specification for
the for example macro (see Argument Evaluation).
(defmacro for (var from init to final do &rest body)
"Execute a simple \"for\" loop.
For example, (for i from 1 to 10 do (print i))."
(declare (debug (symbolp "from" form "to" form "do" &rest form)))
...)
The Edebug specification says which parts of a call to the macro are
forms to be evaluated. For simple macros, the specification
often looks very similar to the formal argument list of the macro
definition, but specifications are much more general than macro
arguments. See Defining Macros, for more explanation of
the declare form.
Take care to ensure that the specifications are known to Edebug when
you instrument code. If you are instrumenting a function from a file
that uses eval-when-compile to require another file containing
macro definitions, you may need to explicitly load that file.
You can also define an edebug specification for a macro separately
from the macro definition with def-edebug-spec. Adding
debug declarations is preferred, and more convenient, for macro
definitions in Lisp, but def-edebug-spec makes it possible to
define Edebug specifications for special forms implemented in C.
Specify which expressions of a call to macro macro are forms to be evaluated. specification should be the edebug specification. Neither argument is evaluated.
The macro argument can actually be any symbol, not just a macro name.
Here is a table of the possibilities for specification and how each directs processing of arguments.
t0If a macro has no Edebug specification, neither through a debug
declaration nor through a def-edebug-spec call, the variable
edebug-eval-macro-args comes into play.
This controls the way Edebug treats macro arguments with no explicit Edebug specification. If it is
nil(the default), none of the arguments is instrumented for evaluation. Otherwise, all arguments are instrumented.
A specification list is required for an Edebug specification if
some arguments of a macro call are evaluated while others are not. Some
elements in a specification list match one or more arguments, but others
modify the processing of all following elements. The latter, called
specification keywords, are symbols beginning with `&' (such
as &optional).
A specification list may contain sublists, which match arguments that are themselves lists, or it may contain vectors used for grouping. Sublists and groups thus subdivide the specification list into a hierarchy of levels. Specification keywords apply only to the remainder of the sublist or group they are contained in.
When a specification list involves alternatives or repetition, matching it against an actual macro call may require backtracking. For more details, see Backtracking.
Edebug specifications provide the power of regular expression matching, plus some context-free grammar constructs: the matching of sublists with balanced parentheses, recursive processing of forms, and recursion via indirect specifications.
Here's a table of the possible elements of a specification list, with their meanings (see Specification Examples, for the referenced examples):
sexpformplacebody&rest form. See &rest below.
function-formquote rather than
function, since it instruments the body of the lambda expression
either way.
lambda-expr&optionalTo make just a few elements optional, followed by non-optional elements,
use [&optional specs...]. To specify that several
elements must all match or none, use &optional
[specs...]. See the defun example.
&restTo repeat only a few elements, use [&rest specs...].
To specify several elements that must all match on every repetition, use
&rest [specs...].
&or&or
specification fails.
Each list element following &or is a single alternative. To
group two or more list elements as a single alternative, enclose them in
[...].
¬&or, but if any of them match, the specification fails. If none
of them match, nothing is matched, but the ¬ specification
succeeds.
&define&define keyword should be the first element in
a list specification.
nilgatelet example.
If the symbol has an Edebug specification, this indirect
specification should be either a list specification that is used in
place of the symbol, or a function that is called to process the
arguments. The specification may be defined with def-edebug-spec
just as for macros. See the defun example.
Otherwise, the symbol should be a predicate. The predicate is called
with the argument, and if the predicate returns nil, the
specification fails and the argument is not instrumented.
Some suitable predicates include symbolp, integerp,
stringp, vectorp, and atom.
[elements...]
"string"
'symbol, where the name
of symbol is the string, but the string form is preferred.
(vector elements...)
(elements...)
A sublist specification may be a dotted list and the corresponding list
argument may then be a dotted list. Alternatively, the last cdr of a
dotted list specification may be another sublist specification (via a
grouping or an indirect specification, e.g., (spec . [(more
specs...)])) whose elements match the non-dotted list arguments.
This is useful in recursive specifications such as in the backquote
example. Also see the description of a nil specification
above for terminating such recursion.
Note that a sublist specification written as (specs . nil)
is equivalent to (specs), and (specs .
(sublist-elements...)) is equivalent to (specs
sublist-elements...).
Here is a list of additional specifications that may appear only after
&define. See the defun example.
nameA defining form is not required to have a name field; and it may have
multiple name fields.
:name:name should be a symbol; it is used as an additional
name component for the definition. You can use this to add a unique,
static component to the name of the definition. It may be used more
than once.
arglambda-listdef-bodybody, described above, but a definition body must be instrumented
with a different Edebug call that looks up information associated with
the definition. Use def-body for the highest level list of forms
within the definition.
def-formdef-body, except it is used to match a single form rather than
a list of forms. As a special case, def-form also means that
tracing information is not output when the form is executed. See the
interactive example.
If a specification fails to match at some point, this does not necessarily mean a syntax error will be signaled; instead, backtracking will take place until all alternatives have been exhausted. Eventually every element of the argument list must be matched by some element in the specification, and every required element in the specification must match some argument.
When a syntax error is detected, it might not be reported until much
later, after higher-level alternatives have been exhausted, and with the
point positioned further from the real error. But if backtracking is
disabled when an error occurs, it can be reported immediately. Note
that backtracking is also reenabled automatically in several situations;
when a new alternative is established by &optional,
&rest, or &or, or at the start of processing a sublist,
group, or indirect specification. The effect of enabling or disabling
backtracking is limited to the remainder of the level currently being
processed and lower levels.
Backtracking is disabled while matching any of the
form specifications (that is, form, body, def-form, and
def-body). These specifications will match any form so any error
must be in the form itself rather than at a higher level.
Backtracking is also disabled after successfully matching a quoted
symbol or string specification, since this usually indicates a
recognized construct. But if you have a set of alternative constructs that
all begin with the same symbol, you can usually work around this
constraint by factoring the symbol out of the alternatives, e.g.,
["foo" &or [first case] [second case] ...].
Most needs are satisfied by these two ways that backtracking is
automatically disabled, but occasionally it is useful to explicitly
disable backtracking by using the gate specification. This is
useful when you know that no higher alternatives could apply. See the
example of the let specification.
It may be easier to understand Edebug specifications by studying the examples provided here.
A let special form has a sequence of bindings and a body. Each
of the bindings is either a symbol or a sublist with a symbol and
optional expression. In the specification below, notice the gate
inside of the sublist to prevent backtracking once a sublist is found.
(def-edebug-spec let
((&rest
&or symbolp (gate symbolp &optional form))
body))
Edebug uses the following specifications for defun and the
associated argument list and interactive specifications. It is
necessary to handle interactive forms specially since an expression
argument is actually evaluated outside of the function body. (The
specification for defmacro is very similar to that for
defun, but allows for the declare statement.)
(def-edebug-spec defun
(&define name lambda-list
[&optional stringp] ; Match the doc string, if present.
[&optional ("interactive" interactive)]
def-body))
(def-edebug-spec lambda-list
(([&rest arg]
[&optional ["&optional" arg &rest arg]]
&optional ["&rest" arg]
)))
(def-edebug-spec interactive
(&optional &or stringp def-form)) ; Notice: def-form
The specification for backquote below illustrates how to match
dotted lists and use nil to terminate recursion. It also
illustrates how components of a vector may be matched. (The actual
specification defined by Edebug is a little different, and does not
support dotted lists because doing so causes very deep recursion that
could fail.)
(def-edebug-spec \` (backquote-form)) ; Alias just for clarity.
(def-edebug-spec backquote-form
(&or ([&or "," ",@"] &or ("quote" backquote-form) form)
(backquote-form . [&or nil backquote-form])
(vector &rest backquote-form)
sexp))
These options affect the behavior of Edebug:
Functions to call before Edebug is used. Each time it is set to a new value, Edebug will call those functions once and then reset
edebug-setup-hooktonil. You could use this to load up Edebug specifications associated with a package you are using, but only when you also use Edebug. See Instrumenting.
If this is non-
nil, normal evaluation of defining forms such asdefunanddefmacroinstruments them for Edebug. This applies toeval-defun,eval-region,eval-buffer, andeval-current-buffer.Use the command M-x edebug-all-defs to toggle the value of this option. See Instrumenting.
If this is non-
nil, the commandseval-defun,eval-region,eval-buffer, andeval-current-bufferinstrument all forms, even those that don't define anything. This doesn't apply to loading or evaluations in the minibuffer.Use the command M-x edebug-all-forms to toggle the value of this option. See Instrumenting.
If this is non-
nil, Edebug saves and restores the window configuration. That takes some time, so if your program does not care what happens to the window configurations, it is better to set this variable tonil.If the value is a list, only the listed windows are saved and restored.
You can use the W command in Edebug to change this variable interactively. See Edebug Display Update.
If this is non-
nil, Edebug saves and restores point in all displayed buffers.Saving and restoring point in other buffers is necessary if you are debugging code that changes the point of a buffer that is displayed in a non-selected window. If Edebug or the user then selects the window, point in that buffer will move to the window's value of point.
Saving and restoring point in all buffers is expensive, since it requires selecting each window twice, so enable this only if you need it. See Edebug Display Update.
If this variable is non-
nil, it specifies the initial execution mode for Edebug when it is first activated. Possible values arestep,next,go,Go-nonstop,trace,Trace-fast,continue, andContinue-fast.The default value is
step. This variable can be set interactively with C-x C-a C-m (edebug-set-initial-mode). See Edebug Execution Modes.
If this is non-
nil, trace each function entry and exit. Tracing output is displayed in a buffer named *edebug-trace*, one function entry or exit per line, indented by the recursion level.Also see
edebug-tracing, in Trace Buffer.
If non-
nil, Edebug tests coverage of all expressions debugged. See Coverage Testing.
If non-
nil, continue defining or executing any keyboard macro that is executing outside of Edebug. Use this with caution since it is not debugged. See Edebug Execution Modes.
If non-
nil, Edebug tries to remove any of its own instrumentation when showing the results of expressions. This is relevant when debugging macros where the results of expressions are themselves instrumented expressions. As a very artificial example, suppose that the example functionfachas been instrumented, and consider a macro of the form:(defmacro test () "Edebug example." (if (symbol-function 'fac) ...))If you instrument the
testmacro and step through it, then by default the result of thesymbol-functioncall has numerousedebug-afterandedebug-beforeforms, which can make it difficult to see the actual result. Ifedebug-unwrap-resultsis non-nil, Edebug tries to remove these forms from the result.
Edebug binds
debug-on-errorto this value, ifdebug-on-errorwas previouslynil. See Trapping Errors.
Edebug binds
debug-on-quitto this value, ifdebug-on-quitwas previouslynil. See Trapping Errors.
If you change the values of edebug-on-error or
edebug-on-quit while Edebug is active, their values won't be used
until the next time Edebug is invoked via a new command.
If non-
nil, an expression to test for at every stop point. If the result is non-nil, then break. Errors are ignored. See Global Break Condition.
The Lisp reader reports invalid syntax, but cannot say where the real problem is. For example, the error `End of file during parsing' in evaluating an expression indicates an excess of open parentheses (or square brackets). The reader detects this imbalance at the end of the file, but it cannot figure out where the close parenthesis should have been. Likewise, `Invalid read syntax: ")"' indicates an excess close parenthesis or missing open parenthesis, but does not say where the missing parenthesis belongs. How, then, to find what to change?
If the problem is not simply an imbalance of parentheses, a useful technique is to try C-M-e at the beginning of each defun, and see if it goes to the place where that defun appears to end. If it does not, there is a problem in that defun.
However, unmatched parentheses are the most common syntax errors in Lisp, and we can give further advice for those cases. (In addition, just moving point through the code with Show Paren mode enabled might find the mismatch.)
The first step is to find the defun that is unbalanced. If there is an excess open parenthesis, the way to do this is to go to the end of the file and type C-u C-M-u. This will move you to the beginning of the first defun that is unbalanced.
The next step is to determine precisely what is wrong. There is no way to be sure of this except by studying the program, but often the existing indentation is a clue to where the parentheses should have been. The easiest way to use this clue is to reindent with C-M-q and see what moves. But don't do this yet! Keep reading, first.
Before you do this, make sure the defun has enough close parentheses. Otherwise, C-M-q will get an error, or will reindent all the rest of the file until the end. So move to the end of the defun and insert a close parenthesis there. Don't use C-M-e to move there, since that too will fail to work until the defun is balanced.
Now you can go to the beginning of the defun and type C-M-q. Usually all the lines from a certain point to the end of the function will shift to the right. There is probably a missing close parenthesis, or a superfluous open parenthesis, near that point. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fit the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
To deal with an excess close parenthesis, first go to the beginning of the file, then type C-u -1 C-M-u to find the end of the first unbalanced defun.
Then find the actual matching close parenthesis by typing C-M-f at the beginning of that defun. This will leave you somewhere short of the place where the defun ought to end. It is possible that you will find a spurious close parenthesis in that vicinity.
If you don't see a problem at that point, the next thing to do is to type C-M-q at the beginning of the defun. A range of lines will probably shift left; if so, the missing open parenthesis or spurious close parenthesis is probably near the first of those lines. (However, don't assume this is true; study the code to make sure.) Once you have found the discrepancy, undo the C-M-q with C-_, since the old indentation is probably appropriate to the intended parentheses.
After you think you have fixed the problem, use C-M-q again. If the old indentation actually fits the intended nesting of parentheses, and you have put back those parentheses, C-M-q should not change anything.
You can do coverage testing for a file of Lisp code by loading the
testcover library and using the command M-x
testcover-start <RET> file <RET> to instrument the
code. Then test your code by calling it one or more times. Then use
the command M-x testcover-mark-all to display colored highlights
on the code to show where coverage is insufficient. The command
M-x testcover-next-mark will move point forward to the next
highlighted spot.
Normally, a red highlight indicates the form was never completely
evaluated; a brown highlight means it always evaluated to the same
value (meaning there has been little testing of what is done with the
result). However, the red highlight is skipped for forms that can't
possibly complete their evaluation, such as error. The brown
highlight is skipped for forms that are expected to always evaluate to
the same value, such as (setq x 14).
For difficult cases, you can add do-nothing macros to your code to give advice to the test coverage tool.
Evaluate form and return its value, but inform coverage testing that form's value should always be the same.
Evaluate form, informing coverage testing that form should never return. If it ever does return, you get a run-time error.
Edebug also has a coverage testing feature (see Coverage Testing). These features partly duplicate each other, and it would be cleaner to combine them.
If your program is working correctly, but you want to make it run more quickly or efficiently, the first thing to do is profile your code so that you know how it is using resources. If you find that one particular function is responsible for a significant portion of the runtime, you can start looking for ways to optimize that piece.
Emacs has built-in support for this. To begin profiling, type M-x profiler-start. You can choose to profile by processor usage, memory usage, or both. After doing some work, type M-x profiler-report to display a summary buffer for each resource that you chose to profile. The names of the report buffers include the times at which the reports were generated, so you can generate another report later on without erasing previous results. When you have finished profiling, type M-x profiler-stop (there is a small overhead associated with profiling).
The profiler report buffer shows, on each line, a function that was called, followed by how much resource (processor or memory) it used in absolute and percentage times since profiling started. If a given line has a `+' symbol at the left-hand side, you can expand that line by typing <RET>, in order to see the function(s) called by the higher-level function. Pressing <RET> again will collapse back to the original state.
Press j or mouse-2 to jump to the definition of a function. Press d to view a function's documentation. You can save a profile to a file using C-x C-w. You can compare two profiles using =.
The elp library offers an alternative approach. See the file elp.el for instructions.
You can check the speed of individual Emacs Lisp forms using the
benchmark library. See the functions benchmark-run and
benchmark-run-compiled in benchmark.el.
To profile Emacs at the level of its C code, you can build it using the --enable-profiling option of configure. When Emacs exits, it generates a file gmon.out that you can examine using the gprof utility. This feature is mainly useful for debugging Emacs. It actually stops the Lisp-level M-x profiler-... commands described above from working.
Printing and reading are the operations of converting Lisp objects to textual form and vice versa. They use the printed representations and read syntax described in Lisp Data Types.
This chapter describes the Lisp functions for reading and printing. It also describes streams, which specify where to get the text (if reading) or where to put it (if printing).
Reading a Lisp object means parsing a Lisp expression in textual
form and producing a corresponding Lisp object. This is how Lisp
programs get into Lisp from files of Lisp code. We call the text the
read syntax of the object. For example, the text `(a . 5)'
is the read syntax for a cons cell whose car is a and whose
cdr is the number 5.
Printing a Lisp object means producing text that represents that object—converting the object to its printed representation (see Printed Representation). Printing the cons cell described above produces the text `(a . 5)'.
Reading and printing are more or less inverse operations: printing the
object that results from reading a given piece of text often produces
the same text, and reading the text that results from printing an object
usually produces a similar-looking object. For example, printing the
symbol foo produces the text `foo', and reading that text
returns the symbol foo. Printing a list whose elements are
a and b produces the text `(a b)', and reading that
text produces a list (but not the same list) with elements a
and b.
However, these two operations are not precisely inverse to each other. There are three kinds of exceptions:
Most of the Lisp functions for reading text take an input stream as an argument. The input stream specifies where or how to get the characters of the text to be read. Here are the possible types of input stream:
tt used as a stream means that the input is read from the
minibuffer. In fact, the minibuffer is invoked once and the text
given by the user is made into a string that is then used as the
input stream. If Emacs is running in batch mode, standard input is used
instead of the minibuffer. For example,
(message "%s" (read t))
will read a Lisp expression from standard input and print the result
to standard output.
nilnil supplied as an input stream means to use the value of
standard-input instead; that value is the default input
stream, and must be a non-nil input stream.
Here is an example of reading from a stream that is a buffer, showing where point is located before and after:
---------- Buffer: foo ----------
This-!- is the contents of foo.
---------- Buffer: foo ----------
(read (get-buffer "foo"))
=> is
(read (get-buffer "foo"))
=> the
---------- Buffer: foo ----------
This is the-!- contents of foo.
---------- Buffer: foo ----------
Note that the first read skips a space. Reading skips any amount of whitespace preceding the significant text.
Here is an example of reading from a stream that is a marker,
initially positioned at the beginning of the buffer shown. The value
read is the symbol This.
---------- Buffer: foo ----------
This is the contents of foo.
---------- Buffer: foo ----------
(setq m (set-marker (make-marker) 1 (get-buffer "foo")))
=> #<marker at 1 in foo>
(read m)
=> This
m
=> #<marker at 5 in foo> ;; Before the first space.
Here we read from the contents of a string:
(read "(When in) the course")
=> (When in)
The following example reads from the minibuffer. The
prompt is: `Lisp expression: '. (That is always the prompt
used when you read from the stream t.) The user's input is shown
following the prompt.
(read t)
=> 23
---------- Buffer: Minibuffer ----------
Lisp expression: 23 <RET>
---------- Buffer: Minibuffer ----------
Finally, here is an example of a stream that is a function, named
useless-stream. Before we use the stream, we initialize the
variable useless-list to a list of characters. Then each call to
the function useless-stream obtains the next character in the list
or unreads a character by adding it to the front of the list.
(setq useless-list (append "XY()" nil))
=> (88 89 40 41)
(defun useless-stream (&optional unread)
(if unread
(setq useless-list (cons unread useless-list))
(prog1 (car useless-list)
(setq useless-list (cdr useless-list)))))
=> useless-stream
Now we read using the stream thus constructed:
(read 'useless-stream)
=> XY
useless-list
=> (40 41)
Note that the open and close parentheses remain in the list. The Lisp
reader encountered the open parenthesis, decided that it ended the
input, and unread it. Another attempt to read from the stream at this
point would read `()' and return nil.
This section describes the Lisp functions and variables that pertain to reading.
In the functions below, stream stands for an input stream (see
the previous section). If stream is nil or omitted, it
defaults to the value of standard-input.
An end-of-file error is signaled if reading encounters an
unterminated list, vector, or string.
This function reads one textual Lisp expression from stream, returning it as a Lisp object. This is the basic Lisp input function.
This function reads the first textual Lisp expression from the text in string. It returns a cons cell whose car is that expression, and whose cdr is an integer giving the position of the next remaining character in the string (i.e., the first one not read).
If start is supplied, then reading begins at index start in the string (where the first character is at index 0). If you specify end, then reading is forced to stop just before that index, as if the rest of the string were not there.
For example:
(read-from-string "(setq x 55) (setq y 5)") => ((setq x 55) . 11) (read-from-string "\"A short string\"") => ("A short string" . 16) ;; Read starting at the first character. (read-from-string "(list 112)" 0) => ((list 112) . 10) ;; Read starting at the second character. (read-from-string "(list 112)" 1) => (list . 5) ;; Read starting at the seventh character, ;; and stopping at the ninth. (read-from-string "(list 112)" 6 8) => (11 . 8)
This variable holds the default input stream—the stream that
readuses when the stream argument isnil. The default ist, meaning use the minibuffer.
If non-
nil, this variable enables the reading of circular and shared structures. See Circular Objects. Its default value ist.
When reading or writing from the standard input/output streams of the Emacs process in batch mode, it is sometimes required to make sure any arbitrary binary data will be read/written verbatim, and/or that no translation of newlines to or from CR-LF pairs is performed. This issue does not exist on Posix hosts, only on MS-Windows and MS-DOS. The following function allows you to control the I/O mode of any standard stream of the Emacs process.
Switch stream into binary or text I/O mode. If mode is non-
nil, switch to binary mode, otherwise switch to text mode. The value of stream can be one ofstdin,stdout, orstderr. This function flushes any pending output data of stream as a side effect, and returns the previous value of I/O mode for stream. On Posix hosts, it always returns a non-nilvalue and does nothing except flushing pending output.
An output stream specifies what to do with the characters produced by printing. Most print functions accept an output stream as an optional argument. Here are the possible types of output stream:
tnilnil specified as an output stream means to use the value of
standard-output instead; that value is the default output
stream, and must not be nil.
Many of the valid output streams are also valid as input streams. The difference between input and output streams is therefore more a matter of how you use a Lisp object, than of different types of object.
Here is an example of a buffer used as an output stream. Point is initially located as shown immediately before the `h' in `the'. At the end, point is located directly before that same `h'.
---------- Buffer: foo ----------
This is t-!-he contents of foo.
---------- Buffer: foo ----------
(print "This is the output" (get-buffer "foo"))
=> "This is the output"
---------- Buffer: foo ----------
This is t
"This is the output"
-!-he contents of foo.
---------- Buffer: foo ----------
Now we show a use of a marker as an output stream. Initially, the
marker is in buffer foo, between the `t' and the `h' in
the word `the'. At the end, the marker has advanced over the
inserted text so that it remains positioned before the same `h'.
Note that the location of point, shown in the usual fashion, has no
effect.
---------- Buffer: foo ----------
This is the -!-output
---------- Buffer: foo ----------
(setq m (copy-marker 10))
=> #<marker at 10 in foo>
(print "More output for foo." m)
=> "More output for foo."
---------- Buffer: foo ----------
This is t
"More output for foo."
he -!-output
---------- Buffer: foo ----------
m
=> #<marker at 34 in foo>
The following example shows output to the echo area:
(print "Echo Area output" t)
=> "Echo Area output"
---------- Echo Area ----------
"Echo Area output"
---------- Echo Area ----------
Finally, we show the use of a function as an output stream. The
function eat-output takes each character that it is given and
conses it onto the front of the list last-output (see Building Lists). At the end, the list contains all the characters output, but
in reverse order.
(setq last-output nil)
=> nil
(defun eat-output (c)
(setq last-output (cons c last-output)))
=> eat-output
(print "This is the output" 'eat-output)
=> "This is the output"
last-output
=> (10 34 116 117 112 116 117 111 32 101 104
116 32 115 105 32 115 105 104 84 34 10)
Now we can put the output in the proper order by reversing the list:
(concat (nreverse last-output))
=> "
\"This is the output\"
"
Calling concat converts the list to a string so you can see its
contents more clearly.
This section describes the Lisp functions for printing Lisp objects—converting objects into their printed representation.
Some of the Emacs printing functions add quoting characters to the output when necessary so that it can be read properly. The quoting characters used are `"' and `\'; they distinguish strings from symbols, and prevent punctuation characters in strings and symbols from being taken as delimiters when reading. See Printed Representation, for full details. You specify quoting or no quoting by the choice of printing function.
If the text is to be read back into Lisp, then you should print with quoting characters to avoid ambiguity. Likewise, if the purpose is to describe a Lisp object clearly for a Lisp programmer. However, if the purpose of the output is to look nice for humans, then it is usually better to print without quoting.
Lisp objects can refer to themselves. Printing a self-referential object in the normal way would require an infinite amount of text, and the attempt could cause infinite recursion. Emacs detects such recursion and prints `#level' instead of recursively printing an object already being printed. For example, here `#0' indicates a recursive reference to the object at level 0 of the current print operation:
(setq foo (list nil))
=> (nil)
(setcar foo foo)
=> (#0)
In the functions below, stream stands for an output stream.
(See the previous section for a description of output streams.) If
stream is nil or omitted, it defaults to the value of
standard-output.
The
(progn (print 'The\ cat\ in) (print "the hat") (print " came back")) -| -| The\ cat\ in -| -| "the hat" -| -| " came back" => " came back"
This function outputs the printed representation of object to stream. It does not print newlines to separate output as
(progn (prin1 'The\ cat\ in) (prin1 "the hat") (prin1 " came back")) -| The\ cat\ in"the hat"" came back" => " came back"
This function outputs the printed representation of object to stream. It returns object.
This function is intended to produce output that is readable by people, not by
read, so it doesn't insert quoting characters and doesn't put double-quotes around the contents of strings. It does not add any spacing between calls.(progn (princ 'The\ cat) (princ " in the \"hat\"")) -| The cat in the "hat" => " in the \"hat\""
This function outputs a newline to stream. The name stands for “terminate print”. If ensure is non-
nilno newline is printed if stream is already at the beginning of a line. Note in this case stream can not be a function and an error is signalled if it is. This function returnstif a newline is printed.
This function outputs character to stream. It returns character.
This function returns a string containing the text that
prin1would have printed for the same argument.(prin1-to-string 'foo) => "foo" (prin1-to-string (mark-marker)) => "#<marker at 2773 in strings.texi>"If noescape is non-
nil, that inhibits use of quoting characters in the output. (This argument is supported in Emacs versions 19 and later.)(prin1-to-string "foo") => "\"foo\"" (prin1-to-string "foo" t) => "foo"See
format, in Formatting Strings, for other ways to obtain the printed representation of a Lisp object as a string.
This macro executes the body forms with
standard-outputset up to feed output into a string. Then it returns that string.For example, if the current buffer name is `foo',
(with-output-to-string (princ "The buffer is ") (princ (buffer-name)))returns
"The buffer is foo".
This function outputs object to stream, just like
prin1, but does it in a prettier way. That is, it'll indent and fill the object to make it more readable for humans.
If you need to use binary I/O in batch mode, e.g., use the functions described in this section to write out arbitrary binary data or avoid conversion of newlines on non-Posix hosts, see set-binary-mode.
The value of this variable is the default output stream—the stream that print functions use when the stream argument is
nil. The default ist, meaning display in the echo area.
If this is non-
nil, that means to print quoted forms using abbreviated reader syntax, e.g.,(quote foo)prints as'foo, and(function foo)as#'foo.
If this variable is non-
nil, then newline characters in strings are printed as `\n' and formfeeds are printed as `\f'. Normally these characters are printed as actual newlines and formfeeds.This variable affects the print functions
prin1andprinc. Here is an example usingprin1:(prin1 "a\nb") -| "a -| b" => "a b" (let ((print-escape-newlines t)) (prin1 "a\nb")) -| "a\nb" => "a b"In the second expression, the local binding of
print-escape-newlinesis in effect during the call toprin1, but not during the printing of the result.
If this variable is non-
nil, then unibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functionsprin1andThose functions also use backslash sequences for unibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a multibyte buffer or a marker pointing into one.
If this variable is non-
nil, then multibyte non-ASCII characters in strings are unconditionally printed as backslash sequences by the print functionsprin1andThose functions also use backslash sequences for multibyte non-ASCII characters, regardless of the value of this variable, when the output stream is a unibyte buffer or a marker pointing into one.
The value of this variable is the maximum number of elements to print in any list, vector or bool-vector. If an object being printed has more than this many elements, it is abbreviated with an ellipsis.
If the value is
nil(the default), then there is no limit.(setq print-length 2) => 2 (print '(1 2 3 4 5)) -| (1 2 ...) => (1 2 ...)
The value of this variable is the maximum depth of nesting of parentheses and brackets when printed. Any list or vector at a depth exceeding this limit is abbreviated with an ellipsis. A value of
nil(which is the default) means no limit.
These are the values for
print-lengthandprint-levelused byeval-expression, and thus, indirectly, by many interactive evaluation commands (see Evaluating Emacs-Lisp Expressions).
These variables are used for detecting and reporting circular and shared structure:
If non-
nil, this variable enables detection of circular and shared structure in printing. See Circular Objects.
If non-
nil, this variable enables detection of uninterned symbols (see Creating Symbols) in printing. When this is enabled, uninterned symbols print with the prefix `#:', which tells the Lisp reader to produce an uninterned symbol.
If non-
nil, that means number continuously across print calls. This affects the numbers printed for `#n=' labels and `#m#' references. Don't set this variable withsetq; you should only bind it temporarily totwithlet. When you do that, you should also bindprint-number-tabletonil.
This variable holds a vector used internally by printing to implement the
print-circlefeature. You should not use it except to bind it tonilwhen you bindprint-continuous-numbering.
This variable specifies how to print floating-point numbers. The default is
nil, meaning use the shortest output that represents the number without losing information.To control output format more precisely, you can put a string in this variable. The string should hold a `%'-specification to be used in the C function
sprintf. For further restrictions on what you can use, see the variable's documentation string.
A minibuffer is a special buffer that Emacs commands use to read arguments more complicated than the single numeric prefix argument. These arguments include file names, buffer names, and command names (as in M-x). The minibuffer is displayed on the bottom line of the frame, in the same place as the echo area (see The Echo Area), but only while it is in use for reading an argument.
In most ways, a minibuffer is a normal Emacs buffer. Most operations within a buffer, such as editing commands, work normally in a minibuffer. However, many operations for managing buffers do not apply to minibuffers. The name of a minibuffer always has the form ` *Minibuf-number*', and it cannot be changed. Minibuffers are displayed only in special windows used only for minibuffers; these windows always appear at the bottom of a frame. (Sometimes frames have no minibuffer window, and sometimes a special kind of frame contains nothing but a minibuffer window; see Minibuffers and Frames.)
The text in the minibuffer always starts with the prompt string,
the text that was specified by the program that is using the minibuffer
to tell the user what sort of input to type. This text is marked
read-only so you won't accidentally delete or change it. It is also
marked as a field (see Fields), so that certain motion functions,
including beginning-of-line, forward-word,
forward-sentence, and forward-paragraph, stop at the
boundary between the prompt and the actual text.
The minibuffer's window is normally a single line; it grows
automatically if the contents require more space. Whilst it is
active, you can explicitly resize it temporarily with the window
sizing commands; it reverts to its normal size when the minibuffer is
exited. When the minibuffer is not active, you can resize it
permanently by using the window sizing commands in the frame's other
window, or dragging the mode line with the mouse. (Due to details of
the current implementation, for this to work resize-mini-windows
must be nil.) If the frame contains just a minibuffer, you can
change the minibuffer's size by changing the frame's size.
Use of the minibuffer reads input events, and that alters the values
of variables such as this-command and last-command
(see Command Loop Info). Your program should bind them around the
code that uses the minibuffer, if you do not want that to change them.
Under some circumstances, a command can use a minibuffer even if
there is an active minibuffer; such a minibuffer is called a
recursive minibuffer. The first minibuffer is named
` *Minibuf-1*'. Recursive minibuffers are named by
incrementing the number at the end of the name. (The names begin with
a space so that they won't show up in normal buffer lists.) Of
several recursive minibuffers, the innermost (or most recently
entered) is the active minibuffer. We usually call this the
minibuffer. You can permit or forbid recursive minibuffers by setting
the variable enable-recursive-minibuffers, or by putting
properties of that name on command symbols (See Recursive Mini.)
Like other buffers, a minibuffer uses a local keymap (see Keymaps) to specify special key bindings. The function that invokes the minibuffer also sets up its local map according to the job to be done. See Text from Minibuffer, for the non-completion minibuffer local maps. See Completion Commands, for the minibuffer local maps for completion.
When a minibuffer is inactive, its major mode is
minibuffer-inactive-mode, with keymap
minibuffer-inactive-mode-map. This is only really useful if
the minibuffer is in a separate frame. See Minibuffers and Frames.
When Emacs is running in batch mode, any request to read from the minibuffer actually reads a line from the standard input descriptor that was supplied when Emacs was started. This supports only basic input: none of the special minibuffer features (history, completion, etc.) are available in batch mode.
The most basic primitive for minibuffer input is
read-from-minibuffer, which can be used to read either a string
or a Lisp object in textual form. The function read-regexp is
used for reading regular expressions (see Regular Expressions),
which are a special kind of string. There are also specialized
functions for reading commands, variables, file names, etc.
(see Completion).
In most cases, you should not call minibuffer input functions in the
middle of a Lisp function. Instead, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See Defining Commands.
This function is the most general way to get input from the minibuffer. By default, it accepts arbitrary text and returns it as a string; however, if read is non-
nil, then it usesreadto convert the text into a Lisp object (see Input Functions).The first thing this function does is to activate a minibuffer and display it with prompt (which must be a string) as the prompt. Then the user can edit text in the minibuffer.
When the user types a command to exit the minibuffer,
read-from-minibufferconstructs the return value from the text in the minibuffer. Normally it returns a string containing that text. However, if read is non-nil,read-from-minibufferreads the text and returns the resulting Lisp object, unevaluated. (See Input Functions, for information about reading.)The argument default specifies default values to make available through the history commands. It should be a string, a list of strings, or
nil. The string or strings become the minibuffer's “future history”, available to the user with M-n.If read is non-
nil, then default is also used as the input toread, if the user enters empty input. If default is a list of strings, the first string is used as the input. If default isnil, empty input results in anend-of-fileerror. However, in the usual case (where read isnil),read-from-minibufferignores default when the user enters empty input and returns an empty string,"". In this respect, it differs from all the other minibuffer input functions in this chapter.If keymap is non-
nil, that keymap is the local keymap to use in the minibuffer. If keymap is omitted ornil, the value ofminibuffer-local-mapis used as the keymap. Specifying a keymap is the most important way to customize the minibuffer for various applications such as completion.The argument history specifies a history list variable to use for saving the input and for history commands used in the minibuffer. It defaults to
minibuffer-history. You can optionally specify a starting position in the history list as well. See Minibuffer History.If the variable
minibuffer-allow-text-propertiesis non-nil, then the string that is returned includes whatever text properties were present in the minibuffer. Otherwise all the text properties are stripped when the value is returned.If the argument inherit-input-method is non-
nil, then the minibuffer inherits the current input method (see Input Methods) and the setting ofenable-multibyte-characters(see Text Representations) from whichever buffer was current before entering the minibuffer.Use of initial is mostly deprecated; we recommend using a non-
nilvalue only in conjunction with specifying a cons cell for history. See Initial Input.
This function reads a string from the minibuffer and returns it. The arguments prompt, initial, history and inherit-input-method are used as in
read-from-minibuffer. The keymap used isminibuffer-local-map.The optional argument default is used as in
read-from-minibuffer, except that, if non-nil, it also specifies a default value to return if the user enters null input. As inread-from-minibufferit should be a string, a list of strings, ornil, which is equivalent to an empty string. When default is a string, that string is the default value. When it is a list of strings, the first string is the default value. (All these strings are available to the user in the “future minibuffer history”.)This function works by calling the
read-from-minibufferfunction:(read-string prompt initial history default inherit) == (let ((value (read-from-minibuffer prompt initial nil nil history default inherit))) (if (and (equal value "") default) (if (consp default) (car default) default) value))
This function reads a regular expression as a string from the minibuffer and returns it. If the minibuffer prompt string prompt does not end in `:' (followed by optional whitespace), the function adds `: ' to the end, preceded by the default return value (see below), if that is non-empty.
The optional argument defaults controls the default value to return if the user enters null input, and should be one of: a string;
nil, which is equivalent to an empty string; a list of strings; or a symbol.If defaults is a symbol,
read-regexpconsults the value of the variableread-regexp-defaults-function(see below), and if that is non-niluses it in preference to defaults. The value in this case should be either:
regexp-history-last, which means to use the first element of the appropriate minibuffer history list (see below).- A function of no arguments, whose return value (which should be
nil, a string, or a list of strings) becomes the value of defaults.
read-regexpnow ensures that the result of processing defaults is a list (i.e., if the value isnilor a string, it converts it to a list of one element). To this list,read-regexpthen appends a few potentially useful candidates for input. These are:
- The word or symbol at point.
- The last regexp used in an incremental search.
- The last string used in an incremental search.
- The last string or pattern used in query-replace commands.
The function now has a list of regular expressions that it passes to
read-from-minibufferto obtain the user's input. The first element of the list is the default result in case of empty input. All elements of the list are available to the user as the “future minibuffer history” list (see future list).The optional argument history, if non-
nil, is a symbol specifying a minibuffer history list to use (see Minibuffer History). If it is omitted ornil, the history list defaults toregexp-history.
The function
read-regexpmay use the value of this variable to determine its list of default regular expressions. If non-nil, the value of this variable should be either:
- The symbol
regexp-history-last.- A function of no arguments that returns either
nil, a string, or a list of strings.See
read-regexpabove for details of how these values are used.
If this variable is
nil, thenread-from-minibufferandread-stringstrip all text properties from the minibuffer input before returning it. However,read-no-blanks-input(see below), as well asread-minibufferand related functions (see Reading Lisp Objects With the Minibuffer), and all functions that do minibuffer input with completion, discard text properties unconditionally, regardless of the value of this variable.
This is the default local keymap for reading from the minibuffer. By default, it makes the following bindings:
- C-j
exit-minibuffer
- <RET>
exit-minibuffer
- C-g
abort-recursive-edit
- M-n
- <DOWN>
next-history-element
- M-p
- <UP>
previous-history-element
- M-s
next-matching-history-element
- M-r
previous-matching-history-element
This function reads a string from the minibuffer, but does not allow whitespace characters as part of the input: instead, those characters terminate the input. The arguments prompt, initial, and inherit-input-method are used as in
read-from-minibuffer.This is a simplified interface to the
read-from-minibufferfunction, and passes the value of theminibuffer-local-ns-mapkeymap as the keymap argument for that function. Since the keymapminibuffer-local-ns-mapdoes not rebind C-q, it is possible to put a space into the string, by quoting it.This function discards text properties, regardless of the value of
minibuffer-allow-text-properties.(read-no-blanks-input prompt initial) == (let (minibuffer-allow-text-properties) (read-from-minibuffer prompt initial minibuffer-local-ns-map))
This built-in variable is the keymap used as the minibuffer local keymap in the function
read-no-blanks-input. By default, it makes the following bindings, in addition to those ofminibuffer-local-map:
This section describes functions for reading Lisp objects with the minibuffer.
This function reads a Lisp object using the minibuffer, and returns it without evaluating it. The arguments prompt and initial are used as in
read-from-minibuffer.This is a simplified interface to the
read-from-minibufferfunction:(read-minibuffer prompt initial) == (let (minibuffer-allow-text-properties) (read-from-minibuffer prompt initial nil t))Here is an example in which we supply the string
"(testing)"as initial input:(read-minibuffer "Enter an expression: " (format "%s" '(testing))) ;; Here is how the minibuffer is displayed: ---------- Buffer: Minibuffer ---------- Enter an expression: (testing)-!- ---------- Buffer: Minibuffer ----------The user can type <RET> immediately to use the initial input as a default, or can edit the input.
This function reads a Lisp expression using the minibuffer, evaluates it, then returns the result. The arguments prompt and initial are used as in
read-from-minibuffer.This function simply evaluates the result of a call to
read-minibuffer:(eval-minibuffer prompt initial) == (eval (read-minibuffer prompt initial))
This function reads a Lisp expression in the minibuffer, evaluates it, then returns the result. The difference between this command and
eval-minibufferis that here the initial form is not optional and it is treated as a Lisp object to be converted to printed representation rather than as a string of text. It is printed withprin1, so if it is a string, double-quote characters (`"') appear in the initial text. See Output Functions.In the following example, we offer the user an expression with initial text that is already a valid form:
(edit-and-eval-command "Please edit: " '(forward-word 1)) ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Please edit: (forward-word 1)-!- ---------- Buffer: Minibuffer ----------Typing <RET> right away would exit the minibuffer and evaluate the expression, thus moving point forward one word.
A minibuffer history list records previous minibuffer inputs so the user can reuse them conveniently. It is a variable whose value is a list of strings (previous inputs), most recent first.
There are many separate minibuffer history lists, used for different kinds of inputs. It's the Lisp programmer's job to specify the right history list for each use of the minibuffer.
You specify a minibuffer history list with the optional history
argument to read-from-minibuffer or completing-read.
Here are the possible values for it:
Specifying 0 for startpos is equivalent to just specifying the
symbol variable. previous-history-element will display
the most recent element of the history list in the minibuffer. If you
specify a positive startpos, the minibuffer history functions
behave as if (elt variable (1- startpos)) were the
history element currently shown in the minibuffer.
For consistency, you should also specify that element of the history as the initial minibuffer contents, using the initial argument to the minibuffer input function (see Initial Input).
If you don't specify history, then the default history list
minibuffer-history is used. For other standard history lists,
see below. You can also create your own history list variable; just
initialize it to nil before the first use.
Both read-from-minibuffer and completing-read add new
elements to the history list automatically, and provide commands to
allow the user to reuse items on the list. The only thing your program
needs to do to use a history list is to initialize it and to pass its
name to the input functions when you wish. But it is safe to modify the
list by hand when the minibuffer input functions are not using it.
Emacs functions that add a new element to a history list can also
delete old elements if the list gets too long. The variable
history-length specifies the maximum length for most history
lists. To specify a different maximum length for a particular history
list, put the length in the history-length property of the
history list symbol. The variable history-delete-duplicates
specifies whether to delete duplicates in history.
This function adds a new element newelt, if it isn't the empty string, to the history list stored in the variable history-var, and returns the updated history list. It limits the list length to the value of maxelt (if non-
nil) orhistory-length(described below). The possible values of maxelt have the same meaning as the values ofhistory-length.Normally,
add-to-historyremoves duplicate members from the history list ifhistory-delete-duplicatesis non-nil. However, if keep-all is non-nil, that says not to remove duplicates, and to add newelt to the list even if it is empty.
If the value of this variable is
nil, standard functions that read from the minibuffer don't add new elements to the history list. This lets Lisp programs explicitly manage input history by usingadd-to-history. The default value ist.
The value of this variable specifies the maximum length for all history lists that don't specify their own maximum lengths. If the value is
t, that means there is no maximum (don't delete old elements). If a history list variable's symbol has a non-nilhistory-lengthproperty, it overrides this variable for that particular history list.
If the value of this variable is
t, that means when adding a new history element, all previous identical elements are deleted.
Here are some of the standard minibuffer history list variables:
A history list for arguments to
query-replace(and similar arguments to other commands).
A history list for arguments that are names of extended commands.
A history list for arguments that are Lisp expressions to evaluate.
Several of the functions for minibuffer input have an argument called initial. This is a mostly-deprecated feature for specifying that the minibuffer should start out with certain text, instead of empty as usual.
If initial is a string, the minibuffer starts out containing the text of the string, with point at the end, when the user starts to edit the text. If the user simply types <RET> to exit the minibuffer, it will use the initial input string to determine the value to return.
We discourage use of a non-nil value for
initial, because initial input is an intrusive interface.
History lists and default values provide a much more convenient method
to offer useful default inputs to the user.
There is just one situation where you should specify a string for an initial argument. This is when you specify a cons cell for the history argument. See Minibuffer History.
initial can also be a cons cell of the form (string
. position). This means to insert string in the
minibuffer but put point at position within the string's text.
As a historical accident, position was implemented
inconsistently in different functions. In completing-read,
position's value is interpreted as origin-zero; that is, a value
of 0 means the beginning of the string, 1 means after the first
character, etc. In read-minibuffer, and the other
non-completion minibuffer input functions that support this argument,
1 means the beginning of the string, 2 means after the first character,
etc.
Use of a cons cell as the value for initial arguments is deprecated.
Completion is a feature that fills in the rest of a name
starting from an abbreviation for it. Completion works by comparing the
user's input against a list of valid names and determining how much of
the name is determined uniquely by what the user has typed. For
example, when you type C-x b (switch-to-buffer) and then
type the first few letters of the name of the buffer to which you wish
to switch, and then type <TAB> (minibuffer-complete), Emacs
extends the name as far as it can.
Standard Emacs commands offer completion for names of symbols, files, buffers, and processes; with the functions in this section, you can implement completion for other kinds of names.
The try-completion function is the basic primitive for
completion: it returns the longest determined completion of a given
initial string, with a given set of strings to match against.
The function completing-read provides a higher-level interface
for completion. A call to completing-read specifies how to
determine the list of valid names. The function then activates the
minibuffer with a local keymap that binds a few keys to commands useful
for completion. Other functions provide convenient simple interfaces
for reading certain kinds of names with completion.
The following completion functions have nothing in themselves to do with minibuffers. We describe them here to keep them near the higher-level completion features that do use the minibuffer.
This function returns the longest common substring of all possible completions of string in collection.
collection is called the completion table. Its value must be a list of strings or cons cells, an obarray, a hash table, or a completion function.
try-completioncompares string against each of the permissible completions specified by the completion table. If no permissible completions match, it returnsnil. If there is just one matching completion, and the match is exact, it returnst. Otherwise, it returns the longest initial sequence common to all possible matching completions.If collection is a list, the permissible completions are specified by the elements of the list, each of which should be either a string, or a cons cell whose car is either a string or a symbol (a symbol is converted to a string using
symbol-name). If the list contains elements of any other type, those are ignored.If collection is an obarray (see Creating Symbols), the names of all symbols in the obarray form the set of permissible completions.
If collection is a hash table, then the keys that are strings are the possible completions. Other keys are ignored.
You can also use a function as collection. Then the function is solely responsible for performing completion;
try-completionreturns whatever this function returns. The function is called with three arguments: string, predicate andnil(the third argument is so that the same function can be used inall-completionsand do the appropriate thing in either case). See Programmed Completion.If the argument predicate is non-
nil, then it must be a function of one argument, unless collection is a hash table, in which case it should be a function of two arguments. It is used to test each possible match, and the match is accepted only if predicate returns non-nil. The argument given to predicate is either a string or a cons cell (the car of which is a string) from the alist, or a symbol (not a symbol name) from the obarray. If collection is a hash table, predicate is called with two arguments, the string key and the associated value.In addition, to be acceptable, a completion must also match all the regular expressions in
completion-regexp-list. (Unless collection is a function, in which case that function has to handlecompletion-regexp-listitself.)In the first of the following examples, the string `foo' is matched by three of the alist cars. All of the matches begin with the characters `fooba', so that is the result. In the second example, there is only one possible match, and it is exact, so the return value is
t.(try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4))) => "fooba" (try-completion "foo" '(("barfoo" 2) ("foo" 3))) => tIn the following example, numerous symbols begin with the characters `forw', and all of them begin with the word `forward'. In most of the symbols, this is followed with a `-', but not in all, so no more than `forward' can be completed.
(try-completion "forw" obarray) => "forward"Finally, in the following example, only two of the three possible matches pass the predicate
test(the string `foobaz' is too short). Both of those begin with the string `foobar'.(defun test (s) (> (length (car s)) 6)) => test (try-completion "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) => "foobar"
This function returns a list of all possible completions of string. The arguments to this function are the same as those of
try-completion, and it usescompletion-regexp-listin the same way thattry-completiondoes.If collection is a function, it is called with three arguments: string, predicate and
t; thenall-completionsreturns whatever the function returns. See Programmed Completion.Here is an example, using the function
testshown in the example fortry-completion:(defun test (s) (> (length (car s)) 6)) => test (all-completions "foo" '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) 'test) => ("foobar1" "foobar2")
This function returns non-
nilif string is a valid completion alternative specified by collection and predicate. The arguments are the same as intry-completion. For instance, if collection is a list of strings, this is true if string appears in the list and predicate is satisfied.This function uses
completion-regexp-listin the same way thattry-completiondoes.If predicate is non-
niland if collection contains several strings that are equal to each other, as determined bycompare-stringsaccording tocompletion-ignore-case, then predicate should accept either all or none of them. Otherwise, the return value oftest-completionis essentially unpredictable.If collection is a function, it is called with three arguments, the values string, predicate and
lambda; whatever it returns,test-completionreturns in turn.
This function returns the boundaries of the field on which collection will operate, assuming that string holds the text before point and suffix holds the text after point.
Normally completion operates on the whole string, so for all normal collections, this will always return
(0 . (lengthsuffix)). But more complex completion such as completion on files is done one field at a time. For example, completion of"/usr/sh"will include"/usr/share/"but not"/usr/share/doc"even if"/usr/share/doc"exists. Alsoall-completionson"/usr/sh"will not include"/usr/share/"but only"share/". So if string is"/usr/sh"and suffix is"e/doc",completion-boundarieswill return(5 . 1)which tells us that the collection will only return completion information that pertains to the area after"/usr/"and before"/doc".
If you store a completion alist in a variable, you should mark the
variable as risky by giving it a non-nil
risky-local-variable property. See File Local Variables.
If the value of this variable is non-
nil, case is not considered significant in completion. Withinread-file-name, this variable is overridden byread-file-name-completion-ignore-case(see Reading File Names); withinread-buffer, it is overridden byread-buffer-completion-ignore-case(see High-Level Completion).
This is a list of regular expressions. The completion functions only consider a completion acceptable if it matches all regular expressions in this list, with
case-fold-search(see Searching and Case) bound to the value ofcompletion-ignore-case.
This macro provides a way to initialize the variable var as a collection for completion in a lazy way, not computing its actual contents until they are first needed. You use this macro to produce a value that you store in var. The actual computation of the proper value is done the first time you do completion using var. It is done by calling fun with no arguments. The value fun returns becomes the permanent value of var.
Here is an example:
(defvar foo (lazy-completion-table foo make-my-alist))
There are several functions that take an existing completion table and
return a modified version. completion-table-case-fold returns
a case-insensitive table. completion-table-in-turn and
completion-table-merge combine multiple input tables in
different ways. completion-table-subvert alters a table to use
a different initial prefix. completion-table-with-quoting
returns a table suitable for operating on quoted text.
completion-table-with-predicate filters a table with a
predicate function. completion-table-with-terminator adds a
terminating string.
This section describes the basic interface for reading from the minibuffer with completion.
This function reads a string in the minibuffer, assisting the user by providing completion. It activates the minibuffer with prompt prompt, which must be a string.
The actual completion is done by passing the completion table collection and the completion predicate predicate to the function
try-completion(see Basic Completion). This happens in certain commands bound in the local keymaps used for completion. Some of these commands also calltest-completion. Thus, if predicate is non-nil, it should be compatible with collection andcompletion-ignore-case. See Definition of test-completion.See Programmed Completion, for detailed requirements when collection is a function.
The value of the optional argument require-match determines how the user may exit the minibuffer:
- If
nil, the usual minibuffer exit commands work regardless of the input in the minibuffer.- If
t, the usual minibuffer exit commands won't exit unless the input completes to an element of collection.- If
confirm, the user can exit with any input, but is asked for confirmation if the input is not an element of collection.- If
confirm-after-completion, the user can exit with any input, but is asked for confirmation if the preceding command was a completion command (i.e., one of the commands inminibuffer-confirm-exit-commands) and the resulting input is not an element of collection. See Completion Commands.- Any other value of require-match behaves like
t, except that the exit commands won't exit if it performs completion.However, empty input is always permitted, regardless of the value of require-match; in that case,
completing-readreturns the first element of default, if it is a list;"", if default isnil; or default. The string or strings in default are also available to the user through the history commands.The function
completing-readusesminibuffer-local-completion-mapas the keymap if require-match isnil, and usesminibuffer-local-must-match-mapif require-match is non-nil. See Completion Commands.The argument history specifies which history list variable to use for saving the input and for minibuffer history commands. It defaults to
minibuffer-history. See Minibuffer History.The argument initial is mostly deprecated; we recommend using a non-
nilvalue only in conjunction with specifying a cons cell for history. See Initial Input. For default input, use default instead.If the argument inherit-input-method is non-
nil, then the minibuffer inherits the current input method (see Input Methods) and the setting ofenable-multibyte-characters(see Text Representations) from whichever buffer was current before entering the minibuffer.If the variable
completion-ignore-caseis non-nil, completion ignores case when comparing the input against the possible matches. See Basic Completion. In this mode of operation, predicate must also ignore case, or you will get surprising results.Here's an example of using
completing-read:(completing-read "Complete a foo: " '(("foobar1" 1) ("barfoo" 2) ("foobaz" 3) ("foobar2" 4)) nil t "fo") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- Complete a foo: fo-!- ---------- Buffer: Minibuffer ----------If the user then types <DEL> <DEL> b <RET>,
completing-readreturnsbarfoo.The
completing-readfunction binds variables to pass information to the commands that actually do completion. They are described in the following section.
The value of this variable must be a function, which is called by
completing-readto actually do its work. It should accept the same arguments ascompleting-read. This can be bound to a different function to completely override the normal behavior ofcompleting-read.
This section describes the keymaps, commands and user options used in the minibuffer to do completion.
The value of this variable is the completion table used for completion in the minibuffer. This is the global variable that contains what
completing-readpasses totry-completion. It is used by minibuffer completion commands such asminibuffer-complete-word.
This variable's value is the predicate that
completing-readpasses totry-completion. The variable is also used by the other minibuffer completion functions.
This variable determines whether Emacs asks for confirmation before exiting the minibuffer;
completing-readbinds this variable, and the functionminibuffer-complete-and-exitchecks the value before exiting. If the value isnil, confirmation is not required. If the value isconfirm, the user may exit with an input that is not a valid completion alternative, but Emacs asks for confirmation. If the value isconfirm-after-completion, the user may exit with an input that is not a valid completion alternative, but Emacs asks for confirmation if the user submitted the input right after any of the completion commands inminibuffer-confirm-exit-commands.
This variable holds a list of commands that cause Emacs to ask for confirmation before exiting the minibuffer, if the require-match argument to
completing-readisconfirm-after-completion. The confirmation is requested if the user attempts to exit the minibuffer immediately after calling any command in this list.
This function completes the minibuffer contents by at most a single word. Even if the minibuffer contents have only one completion,
minibuffer-complete-worddoes not add any characters beyond the first character that is not a word constituent. See Syntax Tables.
This function completes the minibuffer contents, and exits if confirmation is not required, i.e., if
minibuffer-completion-confirmisnil. If confirmation is required, it is given by repeating this command immediately—the command is programmed to work without confirmation when run twice in succession.
This function creates a list of the possible completions of the current minibuffer contents. It works by calling
all-completionsusing the value of the variableminibuffer-completion-tableas the collection argument, and the value ofminibuffer-completion-predicateas the predicate argument. The list of completions is displayed as text in a buffer named *Completions*.
This function displays completions to the stream in
standard-output, usually a buffer. (See Read and Print, for more information about streams.) The argument completions is normally a list of completions just returned byall-completions, but it does not have to be. Each element may be a symbol or a string, either of which is simply printed. It can also be a list of two strings, which is printed as if the strings were concatenated. The first of the two strings is the actual completion, the second string serves as annotation.This function is called by
minibuffer-completion-help. A common way to use it is together withwith-output-to-temp-buffer, like this:(with-output-to-temp-buffer "*Completions*" (display-completion-list (all-completions (buffer-string) my-alist)))
If this variable is non-
nil, the completion commands automatically display a list of possible completions whenever nothing can be completed because the next character is not uniquely determined.
completing-readuses this value as the local keymap when an exact match of one of the completions is not required. By default, this keymap makes the following bindings:
- ?
minibuffer-completion-help
- <SPC>
minibuffer-complete-word
- <TAB>
minibuffer-completeand uses
minibuffer-local-mapas its parent keymap (see Definition of minibuffer-local-map).
completing-readuses this value as the local keymap when an exact match of one of the completions is required. Therefore, no keys are bound toexit-minibuffer, the command that exits the minibuffer unconditionally. By default, this keymap makes the following bindings:
- C-j
minibuffer-complete-and-exit
- <RET>
minibuffer-complete-and-exitand uses
minibuffer-local-completion-mapas its parent keymap.
This is a sparse keymap that simply unbinds <SPC>; because filenames can contain spaces. The function
read-file-namecombines this keymap with eitherminibuffer-local-completion-maporminibuffer-local-must-match-map.
This section describes the higher-level convenience functions for reading certain sorts of names with completion.
In most cases, you should not call these functions in the middle of a
Lisp function. When possible, do all minibuffer input as part of
reading the arguments for a command, in the interactive
specification. See Defining Commands.
This function reads the name of a buffer and returns it as a string. It prompts with prompt. The argument default is the default name to use, the value to return if the user exits with an empty minibuffer. If non-
nil, it should be a string, a list of strings, or a buffer. If it is a list, the default value is the first element of this list. It is mentioned in the prompt, but is not inserted in the minibuffer as initial input.The argument prompt should be a string ending with a colon and a space. If default is non-
nil, the function inserts it in prompt before the colon to follow the convention for reading from the minibuffer with a default value (see Programming Tips).The optional argument require-match has the same meaning as in
completing-read. See Minibuffer Completion.The optional argument predicate, if non-
nil, specifies a function to filter the buffers that should be considered: the function will be called with every potential candidate as its argument, and should returnnilto reject the candidate, non-nilto accept it.In the following example, the user enters `minibuffer.t', and then types <RET>. The argument require-match is
t, and the only buffer name starting with the given input is `minibuffer.texi', so that name is the value.(read-buffer "Buffer name: " "foo" t) ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Buffer name (default foo): -!- ---------- Buffer: Minibuffer ---------- ;; The user types minibuffer.t <RET>. => "minibuffer.texi"
This variable, if non-
nil, specifies a function for reading buffer names.read-buffercalls this function instead of doing its usual work, with the same arguments passed toread-buffer.
If this variable is non-
nil,read-bufferignores case when performing completion while reading the buffer name.
This function reads the name of a command and returns it as a Lisp symbol. The argument prompt is used as in
read-from-minibuffer. Recall that a command is anything for whichcommandpreturnst, and a command name is a symbol for whichcommandpreturnst. See Interactive Call.The argument default specifies what to return if the user enters null input. It can be a symbol, a string or a list of strings. If it is a string,
read-commandinterns it before returning it. If it is a list,read-commandinterns the first element of this list. If default isnil, that means no default has been specified; then if the user enters null input, the return value is(intern ""), that is, a symbol whose name is an empty string.(read-command "Command name? ") ;; After evaluation of the preceding expression, ;; the following prompt appears with an empty minibuffer: ---------- Buffer: Minibuffer ---------- Command name? ---------- Buffer: Minibuffer ----------If the user types forward-c <RET>, then this function returns
forward-char.The
read-commandfunction is a simplified interface tocompleting-read. It uses the variableobarrayso as to complete in the set of extant Lisp symbols, and it uses thecommandppredicate so as to accept only command names:(read-command prompt) == (intern (completing-read prompt obarray 'commandp t nil))
This function reads the name of a customizable variable and returns it as a symbol. Its arguments have the same form as those of
read-command. It behaves just likeread-command, except that it uses the predicatecustom-variable-pinstead ofcommandp.
This function reads a string that is a color specification, either the color's name or an RGB hex value such as
#RRRGGGBBB. It prompts with prompt (default:"Color (name or #RGB triplet):") and provides completion for color names, but not for hex RGB values. In addition to names of standard colors, completion candidates include the foreground and background colors at point.Valid RGB values are described in Color Names.
The function's return value is the string typed by the user in the minibuffer. However, when called interactively or if the optional argument convert is non-
nil, it converts any input color name into the corresponding RGB value string and instead returns that. This function requires a valid color specification to be input. Empty color names are allowed when allow-empty is non-niland the user enters null input.Interactively, or when display is non-
nil, the return value is also displayed in the echo area.
See also the functions read-coding-system and
read-non-nil-coding-system, in User-Chosen Coding Systems,
and read-input-method-name, in Input Methods.
The high-level completion functions read-file-name,
read-directory-name, and read-shell-command are designed
to read file names, directory names, and shell commands, respectively.
They provide special features, including automatic insertion of the
default directory.
This function reads a file name, prompting with prompt and providing completion.
As an exception, this function reads a file name using a graphical file dialog instead of the minibuffer, if all of the following are true:
- It is invoked via a mouse command.
- The selected frame is on a graphical display supporting such dialogs.
- The variable
use-dialog-boxis non-nil. See Dialog Boxes.- The directory argument, described below, does not specify a remote file. See Remote Files.
The exact behavior when using a graphical file dialog is platform-dependent. Here, we simply document the behavior when using the minibuffer.
read-file-namedoes not automatically expand the returned file name. You must callexpand-file-nameyourself if an absolute file name is required.The optional argument require-match has the same meaning as in
completing-read. See Minibuffer Completion.The argument directory specifies the directory to use for completing relative file names. It should be an absolute directory name. If the variable
insert-default-directoryis non-nil, directory is also inserted in the minibuffer as initial input. It defaults to the current buffer's value ofdefault-directory.If you specify initial, that is an initial file name to insert in the buffer (after directory, if that is inserted). In this case, point goes at the beginning of initial. The default for initial is
nil—don't insert any file name. To see what initial does, try the command C-x C-v in a buffer visiting a file. Please note: we recommend using default rather than initial in most cases.If default is non-
nil, then the function returns default if the user exits the minibuffer with the same non-empty contents thatread-file-nameinserted initially. The initial minibuffer contents are always non-empty ifinsert-default-directoryis non-nil, as it is by default. default is not checked for validity, regardless of the value of require-match. However, if require-match is non-nil, the initial minibuffer contents should be a valid file (or directory) name. Otherwiseread-file-nameattempts completion if the user exits without any editing, and does not return default. default is also available through the history commands.If default is
nil,read-file-nametries to find a substitute default to use in its place, which it treats in exactly the same way as if it had been specified explicitly. If default isnil, but initial is non-nil, then the default is the absolute file name obtained from directory and initial. If both default and initial areniland the buffer is visiting a file,read-file-nameuses the absolute file name of that file as default. If the buffer is not visiting a file, then there is no default. In that case, if the user types <RET> without any editing,read-file-namesimply returns the pre-inserted contents of the minibuffer.If the user types <RET> in an empty minibuffer, this function returns an empty string, regardless of the value of require-match. This is, for instance, how the user can make the current buffer visit no file using M-x set-visited-file-name.
If predicate is non-
nil, it specifies a function of one argument that decides which file names are acceptable completion alternatives. A file name is an acceptable value if predicate returns non-nilfor it.Here is an example of using
read-file-name:(read-file-name "The file is ") ;; After evaluation of the preceding expression, ;; the following appears in the minibuffer: ---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/-!- ---------- Buffer: Minibuffer ----------Typing manual <TAB> results in the following:
---------- Buffer: Minibuffer ---------- The file is /gp/gnu/elisp/manual.texi-!- ---------- Buffer: Minibuffer ----------If the user types <RET>,
read-file-namereturns the file name as the string"/gp/gnu/elisp/manual.texi".
If non-
nil, this should be a function that accepts the same arguments asread-file-name. Whenread-file-nameis called, it calls this function with the supplied arguments instead of doing its usual work.
If this variable is non-
nil,read-file-nameignores case when performing completion.
This function is like
read-file-namebut allows only directory names as completion alternatives.If default is
niland initial is non-nil,read-directory-nameconstructs a substitute default by combining directory (or the current buffer's default directory if directory isnil) and initial. If both default and initial arenil, this function uses directory as substitute default, or the current buffer's default directory if directory isnil.
This variable is used by
read-file-name, and thus, indirectly, by most commands reading file names. (This includes all commands that use the code letters `f' or `F' in their interactive form. See Code Characters for interactive.) Its value controls whetherread-file-namestarts by placing the name of the default directory in the minibuffer, plus the initial file name, if any. If the value of this variable isnil, thenread-file-namedoes not place any initial input in the minibuffer (unless you specify initial input with the initial argument). In that case, the default directory is still used for completion of relative file names, but is not displayed.If this variable is
niland the initial minibuffer contents are empty, the user may have to explicitly fetch the next history element to access a default value. If the variable is non-nil, the initial minibuffer contents are always non-empty and the user can always request a default value by immediately typing <RET> in an unedited minibuffer. (See above.)For example:
;; Here the minibuffer starts out with the default directory. (let ((insert-default-directory t)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is ~lewis/manual/-!- ---------- Buffer: Minibuffer ---------- ;; Here the minibuffer is empty and only the prompt ;; appears on its line. (let ((insert-default-directory nil)) (read-file-name "The file is ")) ---------- Buffer: Minibuffer ---------- The file is -!- ---------- Buffer: Minibuffer ----------
This function reads a shell command from the minibuffer, prompting with prompt and providing intelligent completion. It completes the first word of the command using candidates that are appropriate for command names, and the rest of the command words as file names.
This function uses
minibuffer-local-shell-command-mapas the keymap for minibuffer input. The history argument specifies the history list to use; if is omitted ornil, it defaults toshell-command-history(see shell-command-history). The optional argument initial specifies the initial content of the minibuffer (see Initial Input). The rest of args, if present, are used as the default and inherit-input-method arguments inread-from-minibuffer(see Text from Minibuffer).
This keymap is used by
read-shell-commandfor completing command and file names that are part of a shell command. It usesminibuffer-local-mapas its parent keymap, and binds <TAB> tocompletion-at-point.
Here are some variables that can be used to alter the default completion behavior.
The value of this variable is a list of completion style (symbols) to use for performing completion. A completion style is a set of rules for generating completions. Each symbol occurring this list must have a corresponding entry in
completion-styles-alist.
This variable stores a list of available completion styles. Each element in the list has the form
(style try-completion all-completions doc)Here, style is the name of the completion style (a symbol), which may be used in the
completion-stylesvariable to refer to this style; try-completion is the function that does the completion; all-completions is the function that lists the completions; and doc is a string describing the completion style.The try-completion and all-completions functions should each accept four arguments: string, collection, predicate, and point. The string, collection, and predicate arguments have the same meanings as in
try-completion(see Basic Completion), and the point argument is the position of point within string. Each function should return a non-nilvalue if it performed its job, andnilif it did not (e.g., if there is no way to complete string according to the completion style).When the user calls a completion command like
minibuffer-complete(see Completion Commands), Emacs looks for the first style listed incompletion-stylesand calls its try-completion function. If this function returnsnil, Emacs moves to the next listed completion style and calls its try-completion function, and so on until one of the try-completion functions successfully performs completion and returns a non-nilvalue. A similar procedure is used for listing completions, via the all-completions functions.See Completion Styles, for a description of the available completion styles.
This variable specifies special completion styles and other completion behaviors to use when completing certain types of text. Its value should be an alist with elements of the form
(category.alist). category is a symbol describing what is being completed; currently, thebuffer,file, andunicode-namecategories are defined, but others can be defined via specialized completion functions (see Programmed Completion). alist is an association list describing how completion should behave for the corresponding category. The following alist keys are supported:
styles- The value should be a list of completion styles (symbols).
cycle- The value should be a value for
completion-cycle-threshold(see Completion Options) for this category.Additional alist entries may be defined in the future.
This variable is used to specify extra properties of the current completion command. It is intended to be let-bound by specialized completion commands. Its value should be a list of property and value pairs. The following properties are supported:
:annotation-function- The value should be a function to add annotations in the completions buffer. This function must accept one argument, a completion, and should either return
nilor a string to be displayed next to the completion.
:exit-function- The value should be a function to run after performing completion. The function should accept two arguments, string and status, where string is the text to which the field was completed, and status indicates what kind of operation happened:
finishedif text is now complete,soleif the text cannot be further completed but completion is not finished, orexactif the text is a valid completion but may be further completed.
Sometimes it is not possible or convenient to create an alist or an obarray containing all the intended possible completions ahead of time. In such a case, you can supply your own function to compute the completion of a given string. This is called programmed completion. Emacs uses programmed completion when completing file names (see File Name Completion), among many other cases.
To use this feature, pass a function as the collection
argument to completing-read. The function
completing-read arranges to pass your completion function along
to try-completion, all-completions, and other basic
completion functions, which will then let your function do all
the work.
The completion function should accept three arguments:
nil if none. The function should call the predicate for each
possible match, and ignore the match if the predicate returns
nil.
niltry-completion operation. The function should
return t if the specified string is a unique and exact match;
if there is more than one match, it should return the common substring
of all matches (if the string is an exact match for one completion
alternative but also matches other longer alternatives, the return
value is the string); if there are no matches, it should return
nil.
tall-completions operation. The function
should return a list of all possible completions of the specified
string.
lambdatest-completion operation. The function
should return t if the specified string is an exact match for
some completion alternative; nil otherwise.
(boundaries . suffix)
completion-boundaries operation. The function
should return (boundaries start . end), where
start is the position of the beginning boundary in the specified
string, and end is the position of the end boundary in
suffix.
metadata(metadata . alist), where alist is an alist whose
elements are described below.
If the flag has any other value, the completion function should return
nil.
The following is a list of metadata entries that a completion function
may return in response to a metadata flag argument:
categorycompletion-category-overrides, the usual
completion behavior is overridden. See Completion Variables.
annotation-functiondisplay-sort-functioncycle-sort-functioncompletion-cycle-threshold is non-nil and the user is
cycling through completion alternatives. See Completion Options. Its argument list and return value are
the same as for display-sort-function.
This function is a convenient way to write a function that can act as a programmed completion function. The argument function should be a function that takes one argument, a string, and returns an alist of possible completions of it. It is allowed to ignore the argument and return a full list of all possible completions. You can think of
completion-table-dynamicas a transducer between that interface and the interface for programmed completion functions.If the optional argument switch-buffer is non-
nil, and completion is performed in the minibuffer, function will be called with current buffer set to the buffer from which the minibuffer was entered.
This is a wrapper for
completion-table-dynamicthat saves the last argument-result pair. This means that multiple lookups with the same argument only need to call function once. This can be useful when a slow operation is involved, such as calling an external process.
Although completion is usually done in the minibuffer, the
completion facility can also be used on the text in ordinary Emacs
buffers. In many major modes, in-buffer completion is performed by
the C-M-i or M-<TAB> command, bound to
completion-at-point. See Symbol Completion. This command uses the abnormal hook variable
completion-at-point-functions:
The value of this abnormal hook should be a list of functions, which are used to compute a completion table for completing the text at point. It can be used by major modes to provide mode-specific completion tables (see Major Mode Conventions).
When the command
completion-at-pointruns, it calls the functions in the list one by one, without any argument. Each function should returnnilif it is unable to produce a completion table for the text at point. Otherwise it should return a list of the form(start end collection . props)start and end delimit the text to complete (which should enclose point). collection is a completion table for completing that text, in a form suitable for passing as the second argument to
try-completion(see Basic Completion); completion alternatives will be generated from this completion table in the usual way, via the completion styles defined incompletion-styles(see Completion Variables). props is a property list for additional information; any of the properties incompletion-extra-propertiesare recognized (see Completion Variables), as well as the following additional ones:
:predicate- The value should be a predicate that completion candidates need to satisfy.
:exclusive- If the value is
no, then if the completion table fails to match the text at point,completion-at-pointmoves on to the next function incompletion-at-point-functionsinstead of reporting a completion failure.Supplying a function for collection is strongly recommended if generating the list of completions is an expensive operation. Emacs may internally call functions in
completion-at-point-functionsmany times, but care about the value of collection for only some of these calls. By supplying a function for collection, Emacs can defer generating completions until necessary. You can use completion-table-dynamic to create a wrapper function:;; Avoid this pattern. (let ((beg ...) (end ...) (my-completions (my-make-completions))) (list beg end my-completions)) ;; Use this instead. (let ((beg ...) (end ...)) (list beg end (completion-table-dynamic (lambda (_) (my-make-completions)))))A function in
completion-at-point-functionsmay also return a function instead of a list as described above. In that case, that returned function is called, with no argument, and it is entirely responsible for performing the completion. We discourage this usage; it is intended to help convert old code to usingcompletion-at-point.The first function in
completion-at-point-functionsto return a non-nilvalue is used bycompletion-at-point. The remaining functions are not called. The exception to this is when there is an:exclusivespecification, as described above.
The following function provides a convenient way to perform completion on an arbitrary stretch of text in an Emacs buffer:
This function completes the text in the current buffer between the positions start and end, using collection. The argument collection has the same meaning as in
try-completion(see Basic Completion).This function inserts the completion text directly into the current buffer. Unlike
completing-read(see Minibuffer Completion), it does not activate the minibuffer.For this function to work, point must be somewhere between start and end.
This section describes functions used to ask the user a yes-or-no
question. The function y-or-n-p can be answered with a single
character; it is useful for questions where an inadvertent wrong answer
will not have serious consequences. yes-or-no-p is suitable for
more momentous questions, since it requires three or four characters to
answer.
If either of these functions is called in a command that was invoked
using the mouse—more precisely, if last-nonmenu-event
(see Command Loop Info) is either nil or a list—then it
uses a dialog box or pop-up menu to ask the question. Otherwise, it
uses keyboard input. You can force use either of the mouse or of keyboard
input by binding last-nonmenu-event to a suitable value around
the call.
Strictly speaking, yes-or-no-p uses the minibuffer and
y-or-n-p does not; but it seems best to describe them together.
This function asks the user a question, expecting input in the echo area. It returns
tif the user types y,nilif the user types n. This function also accepts <SPC> to mean yes and <DEL> to mean no. It accepts C-] to quit, like C-g, because the question might look like a minibuffer and for that reason the user might try to use C-] to get out. The answer is a single character, with no <RET> needed to terminate it. Upper and lower case are equivalent.“Asking the question” means printing prompt in the echo area, followed by the string `(y or n) '. If the input is not one of the expected answers (y, n, <SPC>, <DEL>, or something that quits), the function responds `Please answer y or n.', and repeats the request.
This function does not actually use the minibuffer, since it does not allow editing of the answer. It actually uses the echo area (see The Echo Area), which uses the same screen space as the minibuffer. The cursor moves to the echo area while the question is being asked.
The answers and their meanings, even `y' and `n', are not hardwired, and are specified by the keymap
query-replace-map(see Search and Replace). In particular, if the user enters the special responsesrecenter,scroll-up,scroll-down,scroll-other-window, orscroll-other-window-down(respectively bound to C-l, C-v, M-v, C-M-v and C-M-S-v inquery-replace-map), this function performs the specified window recentering or scrolling operation, and poses the question again.We show successive lines of echo area messages, but only one actually appears on the screen at a time.
Like
y-or-n-p, except that if the user fails to answer within seconds seconds, this function stops waiting and returns default. It works by setting up a timer; see Timers. The argument seconds should be a number.
This function asks the user a question, expecting input in the minibuffer. It returns
tif the user enters `yes',nilif the user types `no'. The user must type <RET> to finalize the response. Upper and lower case are equivalent.
yes-or-no-pstarts by displaying prompt in the echo area, followed by `(yes or no) '. The user must type one of the expected responses; otherwise, the function responds `Please answer yes or no.', waits about two seconds and repeats the request.
yes-or-no-prequires more work from the user thany-or-n-pand is appropriate for more crucial decisions.Here is an example:
(yes-or-no-p "Do you really want to remove everything? ") ;; After evaluation of the preceding expression, ;; the following prompt appears, ;; with an empty minibuffer: ---------- Buffer: minibuffer ---------- Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------If the user first types y <RET>, which is invalid because this function demands the entire word `yes', it responds by displaying these prompts, with a brief pause between them:
---------- Buffer: minibuffer ---------- Please answer yes or no. Do you really want to remove everything? (yes or no) ---------- Buffer: minibuffer ----------
When you have a series of similar questions to ask, such as “Do you
want to save this buffer?” for each buffer in turn, you should use
map-y-or-n-p to ask the collection of questions, rather than
asking each question individually. This gives the user certain
convenient facilities such as the ability to answer the whole series at
once.
This function asks the user a series of questions, reading a single-character answer in the echo area for each one.
The value of list specifies the objects to ask questions about. It should be either a list of objects or a generator function. If it is a function, it should expect no arguments, and should return either the next object to ask about, or
nil, meaning to stop asking questions.The argument prompter specifies how to ask each question. If prompter is a string, the question text is computed like this:
(format prompter object)where object is the next object to ask about (as obtained from list).
If not a string, prompter should be a function of one argument (the next object to ask about) and should return the question text. If the value is a string, that is the question to ask the user. The function can also return
t, meaning do act on this object (and don't ask the user), ornil, meaning ignore this object (and don't ask the user).The argument actor says how to act on the answers that the user gives. It should be a function of one argument, and it is called with each object that the user says yes for. Its argument is always an object obtained from list.
If the argument help is given, it should be a list of this form:
(singular plural action)where singular is a string containing a singular noun that describes the objects conceptually being acted on, plural is the corresponding plural noun, and action is a transitive verb describing what actor does.
If you don't specify help, the default is
("object" "objects" "act on").Each time a question is asked, the user may enter y, Y, or <SPC> to act on that object; n, N, or <DEL> to skip that object; ! to act on all following objects; <ESC> or q to exit (skip all following objects); . (period) to act on the current object and then exit; or C-h to get help. These are the same answers that
query-replaceaccepts. The keymapquery-replace-mapdefines their meaning formap-y-or-n-pas well as forquery-replace; see Search and Replace.You can use action-alist to specify additional possible answers and what they mean. It is an alist of elements of the form
(char function help), each of which defines one additional answer. In this element, char is a character (the answer); function is a function of one argument (an object from list); help is a string.When the user responds with char,
map-y-or-n-pcalls function. If it returns non-nil, the object is considered acted upon, andmap-y-or-n-padvances to the next object in list. If it returnsnil, the prompt is repeated for the same object.Normally,
map-y-or-n-pbindscursor-in-echo-areawhile prompting. But if no-cursor-in-echo-area is non-nil, it does not do that.If
map-y-or-n-pis called in a command that was invoked using the mouse—more precisely, iflast-nonmenu-event(see Command Loop Info) is eithernilor a list—then it uses a dialog box or pop-up menu to ask the question. In this case, it does not use keyboard input or the echo area. You can force use either of the mouse or of keyboard input by bindinglast-nonmenu-eventto a suitable value around the call.The return value of
map-y-or-n-pis the number of objects acted on.
To read a password to pass to another program, you can use the
function read-passwd.
This function reads a password, prompting with prompt. It does not echo the password as the user types it; instead, it echoes `.' for each character in the password. If you want to apply another character to hide the password, let-bind the variable
read-hide-charwith that character.The optional argument confirm, if non-
nil, says to read the password twice and insist it must be the same both times. If it isn't the same, the user has to type it over and over until the last two times match.The optional argument default specifies the default password to return if the user enters empty input. If default is
nil, thenread-passwdreturns the null string in that case.
This section describes some commands meant for use in the minibuffer.
This command exits the active minibuffer. It is normally bound to keys in minibuffer local keymaps.
This command exits the active minibuffer after inserting the last character typed on the keyboard (found in
last-command-event; see Command Loop Info).
This command replaces the minibuffer contents with the value of the nth previous (older) history element.
This command replaces the minibuffer contents with the value of the nth more recent history element.
This command replaces the minibuffer contents with the value of the nth previous (older) history element that matches pattern (a regular expression).
This command replaces the minibuffer contents with the value of the nth next (newer) history element that matches pattern (a regular expression).
This command replaces the minibuffer contents with the value of the nth previous (older) history element that completes the current contents of the minibuffer before the point.
This command replaces the minibuffer contents with the value of the nth next (newer) history element that completes the current contents of the minibuffer before the point.
These functions access and select minibuffer windows, test whether they are active and control how they get resized.
This function returns the currently active minibuffer window, or
nilif there is none.
This function returns the minibuffer window used for frame frame. If frame is
nil, that stands for the current frame. Note that the minibuffer window used by a frame need not be part of that frame—a frame that has no minibuffer of its own necessarily uses some other frame's minibuffer window.
This function specifies window as the minibuffer window to use. This affects where the minibuffer is displayed if you put text in it without invoking the usual minibuffer commands. It has no effect on the usual minibuffer input functions because they all start by choosing the minibuffer window according to the current frame.
This function returns non-
nilif window is a minibuffer window. window defaults to the selected window.
It is not correct to determine whether a given window is a minibuffer by
comparing it with the result of (minibuffer-window), because
there can be more than one minibuffer window if there is more than one
frame.
This function returns non-
nilif window is the currently active minibuffer window.
The following two options control whether minibuffer windows are resized automatically and how large they can get in the process.
This option specifies whether minibuffer windows are resized automatically. The default value is
grow-only, which means that a minibuffer window by default expands automatically to accommodate the text it displays and shrinks back to one line as soon as the minibuffer gets empty. If the value ist, Emacs will always try to fit the height of a minibuffer window to the text it displays (with a minimum of one line). If the value isnil, a minibuffer window never changes size automatically. In that case the window resizing commands (see Resizing Windows) can be used to adjust its height.
This option provides a maximum height for resizing minibuffer windows automatically. A floating-point number specifies a fraction of the frame's height; an integer specifies the maximum number of lines. The default value is 0.25.
These functions access the minibuffer prompt and contents.
This function returns the prompt string of the currently active minibuffer. If no minibuffer is active, it returns
nil.
This function returns the current position of the end of the minibuffer prompt, if a minibuffer is current. Otherwise, it returns the minimum valid buffer position.
This function returns the current display-width of the minibuffer prompt, if a minibuffer is current. Otherwise, it returns zero.
This function returns the editable contents of the minibuffer (that is, everything except the prompt) as a string, if a minibuffer is current. Otherwise, it returns the entire contents of the current buffer.
This is like
minibuffer-contents, except that it does not copy text properties, just the characters themselves. See Text Properties.
This command erases the editable contents of the minibuffer (that is, everything except the prompt), if a minibuffer is current. Otherwise, it erases the entire current buffer.
These functions and variables deal with recursive minibuffers (see Recursive Editing):
This function returns the current depth of activations of the minibuffer, a nonnegative integer. If no minibuffers are active, it returns zero.
If this variable is non-
nil, you can invoke commands (such asfind-file) that use minibuffers even while the minibuffer window is active. Such invocation produces a recursive editing level for a new minibuffer. The outer-level minibuffer is invisible while you are editing the inner one.If this variable is
nil, you cannot invoke minibuffer commands when the minibuffer window is active, not even if you switch to another window to do it.
If a command name has a property enable-recursive-minibuffers
that is non-nil, then the command can use the minibuffer to read
arguments even if it is invoked from the minibuffer. A command can
also achieve this by binding enable-recursive-minibuffers
to t in the interactive declaration (see Using Interactive).
The minibuffer command next-matching-history-element (normally
M-s in the minibuffer) does the latter.
This function returns non-
nilif buffer-or-name is a minibuffer. If buffer-or-name is omitted, it tests the current buffer.
This is a normal hook that is run whenever the minibuffer is entered. See Hooks.
This is a normal hook that is run whenever the minibuffer is exited. See Hooks.
The current value of this variable is used to rebind
help-formlocally inside the minibuffer (see Help Functions).
If the value of this variable is non-
nil, it should be a window object. When the functionscroll-other-windowis called in the minibuffer, it scrolls this window.
This function returns the window that was selected when the minibuffer was entered. If selected window is not a minibuffer window, it returns
nil.
This variable specifies the maximum height for resizing minibuffer windows. If a float, it specifies a fraction of the height of the frame. If an integer, it specifies a number of lines.
This function displays string temporarily at the end of the minibuffer text, for a few seconds, or until the next input event arrives, whichever comes first. The variable
minibuffer-message-timeoutspecifies the number of seconds to wait in the absence of input. It defaults to 2. If args is non-nil, the actual message is obtained by passing string and args throughformat-message. See Formatting Strings.
This is the major mode used in inactive minibuffers. It uses keymap
minibuffer-inactive-mode-map. This can be useful if the minibuffer is in a separate frame. See Minibuffers and Frames.
When you run Emacs, it enters the editor command loop almost immediately. This loop reads key sequences, executes their definitions, and displays the results. In this chapter, we describe how these things are done, and the subroutines that allow Lisp programs to do them.
The first thing the command loop must do is read a key sequence,
which is a sequence of input events that translates into a command.
It does this by calling the function read-key-sequence. Lisp
programs can also call this function (see Key Sequence Input).
They can also read input at a lower level with read-key or
read-event (see Reading One Event), or discard pending
input with discard-input (see Event Input Misc).
The key sequence is translated into a command through the currently
active keymaps. See Key Lookup, for information on how this is done.
The result should be a keyboard macro or an interactively callable
function. If the key is M-x, then it reads the name of another
command, which it then calls. This is done by the command
execute-extended-command (see Interactive Call).
Prior to executing the command, Emacs runs undo-boundary to
create an undo boundary. See Maintaining Undo.
To execute a command, Emacs first reads its arguments by calling
command-execute (see Interactive Call). For commands
written in Lisp, the interactive specification says how to read
the arguments. This may use the prefix argument (see Prefix Command Arguments) or may read with prompting in the minibuffer
(see Minibuffers). For example, the command find-file has
an interactive specification which says to read a file name
using the minibuffer. The function body of find-file does not
use the minibuffer, so if you call find-file as a function from
Lisp code, you must supply the file name string as an ordinary Lisp
function argument.
If the command is a keyboard macro (i.e., a string or vector),
Emacs executes it using execute-kbd-macro (see Keyboard Macros).
This normal hook is run by the editor command loop before it executes each command. At that time,
this-commandcontains the command that is about to run, andlast-commanddescribes the previous command. See Command Loop Info.
This normal hook is run by the editor command loop after it executes each command (including commands terminated prematurely by quitting or by errors). At that time,
this-commandrefers to the command that just ran, andlast-commandrefers to the command before that.This hook is also run when Emacs first enters the command loop (at which point
this-commandandlast-commandare bothnil).
Quitting is suppressed while running pre-command-hook and
post-command-hook. If an error happens while executing one of
these hooks, it does not terminate execution of the hook; instead
the error is silenced and the function in which the error occurred
is removed from the hook.
A request coming into the Emacs server (see Emacs Server) runs these two hooks just as a keyboard command does.
The special form interactive turns a Lisp function into a
command. The interactive form must be located at top-level in
the function body, usually as the first form in the body; this applies
to both lambda expressions (see Lambda Expressions) and
defun forms (see Defining Functions). This form does
nothing during the actual execution of the function; its presence
serves as a flag, telling the Emacs command loop that the function can
be called interactively. The argument of the interactive form
specifies how the arguments for an interactive call should be read.
Alternatively, an interactive form may be specified in a
function symbol's interactive-form property. A non-nil
value for this property takes precedence over any interactive
form in the function body itself. This feature is seldom used.
Sometimes, a function is only intended to be called interactively,
never directly from Lisp. In that case, give the function a
non-nil interactive-only property, either directly
or via declare (see Declare Form). This causes the
byte compiler to warn if the command is called from Lisp. The output
of describe-function will include similar information.
The value of the property can be: a string, which the byte-compiler
will use directly in its warning (it should end with a period, and not
start with a capital, e.g., "use (system-name) instead."); t; any
other symbol, which should be an alternative function to use in Lisp
code.
interactive
This section describes how to write the interactive form that
makes a Lisp function an interactively-callable command, and how to
examine a command's interactive form.
This special form declares that a function is a command, and that it may therefore be called interactively (via M-x or by entering a key sequence bound to it). The argument arg-descriptor declares how to compute the arguments to the command when the command is called interactively.
A command may be called from Lisp programs like any other function, but then the caller supplies the arguments and arg-descriptor has no effect.
The
interactiveform must be located at top-level in the function body, or in the function symbol'sinteractive-formproperty (see Symbol Properties). It has its effect because the command loop looks for it before calling the function (see Interactive Call). Once the function is called, all its body forms are executed; at this time, if theinteractiveform occurs within the body, the form simply returnsnilwithout even evaluating its argument.By convention, you should put the
interactiveform in the function body, as the first top-level form. If there is aninteractiveform in both theinteractive-formsymbol property and the function body, the former takes precedence. Theinteractive-formsymbol property can be used to add an interactive form to an existing function, or change how its arguments are processed interactively, without redefining the function.
There are three possibilities for the argument arg-descriptor:
nil; then the command is called with no
arguments. This leads quickly to an error if the command requires one
or more arguments.
(interactive "P\nbFrobnicate buffer: ")
The code letter `P' sets the command's first argument to the raw command prefix (see Prefix Command Arguments). `bFrobnicate buffer: ' prompts the user with `Frobnicate buffer: ' to enter the name of an existing buffer, which becomes the second and final argument.
The prompt string can use `%' to include previous argument values
(starting with the first argument) in the prompt. This is done using
format-message (see Formatting Strings). For example, here is how
you could read the name of an existing buffer followed by a new name to
give to that buffer:
(interactive "bBuffer to rename: \nsRename buffer %s to: ")
If `*' appears at the beginning of the string, then an error is signaled if the buffer is read-only.
If `@' appears at the beginning of the string, and if the key sequence used to invoke the command includes any mouse events, then the window associated with the first of those events is selected before the command is run.
If `^' appears at the beginning of the string, and if the command
was invoked through shift-translation, set the mark and activate
the region temporarily, or extend an already active region, before the
command is run. If the command was invoked without shift-translation,
and the region is temporarily active, deactivate the region before the
command is run. Shift-translation is controlled on the user level by
shift-select-mode; see Shift Selection.
You can use `*', `@', and ^ together; the order does
not matter. Actual reading of arguments is controlled by the rest of
the prompt string (starting with the first character that is not
`*', `@', or `^').
Providing point or the mark as an argument value is also common, but if you do this and read input (whether using the minibuffer or not), be sure to get the integer values of point or the mark after reading. The current buffer may be receiving subprocess output; if subprocess output arrives while the command is waiting for input, it could relocate point and the mark.
Here's an example of what not to do:
(interactive
(list (region-beginning) (region-end)
(read-string "Foo: " nil 'my-history)))
Here's how to avoid the problem, by examining point and the mark after reading the keyboard input:
(interactive
(let ((string (read-string "Foo: " nil 'my-history)))
(list (region-beginning) (region-end) string)))
Warning: the argument values should not include any data
types that can't be printed and then read. Some facilities save
command-history in a file to be read in the subsequent
sessions; if a command's arguments contain a data type that prints
using `#<...>' syntax, those facilities won't work.
There are, however, a few exceptions: it is ok to use a limited set of
expressions such as (point), (mark),
(region-beginning), and (region-end), because Emacs
recognizes them specially and puts the expression (rather than its
value) into the command history. To see whether the expression you
wrote is one of these exceptions, run the command, then examine
(car command-history).
This function returns the
interactiveform of function. If function is an interactively callable function (see Interactive Call), the value is the command'sinteractiveform(interactivespec), which specifies how to compute its arguments. Otherwise, the value isnil. If function is a symbol, its function definition is used.
interactive
The code character descriptions below contain a number of key words, defined here as follows:
completing-read
(see Completion). ? displays a list of possible completions.
Even though the code letter doesn't use a prompt string, you must follow
it with a newline if it is not the last code character in the string.
Here are the code character descriptions for use with interactive:
fboundp). Existing,
Completion, Prompt.
commandp). Existing,
Completion, Prompt.
default-directory (see File Name Expansion).
Existing, Completion, Default, Prompt.
You use `e' for mouse events and for special system events (see Misc Events). The event list that the command receives depends on the event. See Input Events, which describes the forms of the list for each event in the corresponding subsections.
You can use `e' more than once in a single command's interactive
specification. If the key sequence that invoked the command has
n events that are lists, the nth `e' provides the
nth such event. Events that are not lists, such as function keys
and ASCII characters, do not count where `e' is concerned.
default-directory. Existing, Completion, Default,
Prompt.
nil as
the argument's value. No I/O.
If `k' reads a key sequence that ends with a down-event, it also reads and discards the following up-event. You can get access to that up-event with the `U' code character.
This kind of input is used by commands such as describe-key and
global-set-key.
nil. Can be used after a `k' or
`K' argument to get the up-event that was discarded (if any)
after `k' or `K' read a down-event. If no up-event has been
discarded, `U' provides nil as the argument. No I/O.
custom-variable-p). This reads the variable using
read-variable. See Definition of read-variable. Existing,
Completion, Prompt.
nil. See Coding Systems. Completion,
Existing, Prompt.
nil as the
argument value. Completion, Existing, Prompt.
interactive
Here are some examples of interactive:
(defun foo1 () ;foo1takes no arguments, (interactive) ; just moves forward two words. (forward-word 2)) => foo1 (defun foo2 (n) ;foo2takes one argument, (interactive "^p") ; which is the numeric prefix. ; undershift-select-mode, ; will activate or extend region. (forward-word (* 2 n))) => foo2 (defun foo3 (n) ;foo3takes one argument, (interactive "nCount:") ; which is read with the Minibuffer. (forward-word (* 2 n))) => foo3 (defun three-b (b1 b2 b3) "Select three existing buffers. Put them into three windows, selecting the last one." (interactive "bBuffer1:\nbBuffer2:\nbBuffer3:") (delete-other-windows) (split-window (selected-window) 8) (switch-to-buffer b1) (other-window 1) (split-window (selected-window) 8) (switch-to-buffer b2) (other-window 1) (switch-to-buffer b3)) => three-b (three-b "*scratch*" "declarations.texi" "*mail*") => nil
The macro define-alternatives can be used to define
generic commands. These are interactive functions whose
implementation can be selected from several alternatives, as a matter
of user preference.
Define the new command command, a symbol.
When a user runs M-x command <RET> for the first time, Emacs prompts for which real form of the command to use, and records the selection by way of a custom variable. Using a prefix argument repeats this process of choosing an alternative.
The variable command
-alternativesshould contain an alist with alternative implementations of command. Until this variable is set,define-alternativeshas no effect.If customizations is non-
nil, it should consist of alternatingdefcustomkeywords (typically:groupand:version) and values to add to the declaration of command-alternatives.
After the command loop has translated a key sequence into a command,
it invokes that command using the function command-execute. If
the command is a function, command-execute calls
call-interactively, which reads the arguments and calls the
command. You can also call these functions yourself.
Note that the term “command”, in this context, refers to an interactively callable function (or function-like object), or a keyboard macro. It does not refer to the key sequence used to invoke a command (see Keymaps).
This function returns
tif object is a command. Otherwise, it returnsnil.Commands include strings and vectors (which are treated as keyboard macros), lambda expressions that contain a top-level
interactiveform (see Using Interactive), byte-code function objects made from such lambda expressions, autoload objects that are declared as interactive (non-nilfourth argument toautoload), and some primitive functions. Also, a symbol is considered a command if it has a non-nilinteractive-formproperty, or if its function definition satisfiescommandp.If for-call-interactively is non-
nil, thencommandpreturnstonly for objects thatcall-interactivelycould call—thus, not for keyboard macros.See
documentationin Accessing Documentation, for a realistic example of usingcommandp.
This function calls the interactively callable function command, providing arguments according to its interactive calling specifications. It returns whatever command returns.
If, for instance, you have a function with the following signature:
(defun foo (begin end) (interactive "r") ...)then saying
(call-interactively 'foo)will call
foowith the region (pointandmark) as the arguments.An error is signaled if command is not a function or if it cannot be called interactively (i.e., is not a command). Note that keyboard macros (strings and vectors) are not accepted, even though they are considered commands, because they are not functions. If command is a symbol, then
call-interactivelyuses its function definition.If record-flag is non-
nil, then this command and its arguments are unconditionally added to the listcommand-history. Otherwise, the command is added only if it uses the minibuffer to read an argument. See Command History.The argument keys, if given, should be a vector which specifies the sequence of events to supply if the command inquires which events were used to invoke it. If keys is omitted or
nil, the default is the return value ofthis-command-keys-vector. See Definition of this-command-keys-vector.
This function works like
funcall(see Calling Functions), but it makes the call look like an interactive invocation: a call tocalled-interactively-pinside function will returnt. If function is not a command, it is called without signaling an error.
This function executes command. The argument command must satisfy the
commandppredicate; i.e., it must be an interactively callable function or a keyboard macro.A string or vector as command is executed with
execute-kbd-macro. A function is passed tocall-interactively(see above), along with the record-flag and keys arguments.If command is a symbol, its function definition is used in its place. A symbol with an
autoloaddefinition counts as a command if it was declared to stand for an interactively callable function. Such a definition is handled by loading the specified library and then rechecking the definition of the symbol.The argument special, if given, means to ignore the prefix argument and not clear it. This is used for executing special events (see Special Events).
This function reads a command name from the minibuffer using
completing-read(see Completion). Then it usescommand-executeto call the specified command. Whatever that command returns becomes the value ofexecute-extended-command.If the command asks for a prefix argument, it receives the value prefix-argument. If
execute-extended-commandis called interactively, the current raw prefix argument is used for prefix-argument, and thus passed on to whatever command is run.
execute-extended-commandis the normal definition of M-x, so it uses the string `M-x ' as a prompt. (It would be better to take the prompt from the events used to invokeexecute-extended-command, but that is painful to implement.) A description of the value of the prefix argument, if any, also becomes part of the prompt.(execute-extended-command 3) ---------- Buffer: Minibuffer ---------- 3 M-x forward-word RET ---------- Buffer: Minibuffer ---------- => t
Sometimes a command should display additional visual feedback (such
as an informative message in the echo area) for interactive calls
only. There are three ways to do this. The recommended way to test
whether the function was called using call-interactively is to
give it an optional argument print-message and use the
interactive spec to make it non-nil in interactive
calls. Here's an example:
(defun foo (&optional print-message)
(interactive "p")
(when print-message
(message "foo")))
We use "p" because the numeric prefix argument is never
nil. Defined in this way, the function does display the
message when called from a keyboard macro.
The above method with the additional argument is usually best,
because it allows callers to say “treat this call as interactive”.
But you can also do the job by testing called-interactively-p.
This function returns
twhen the calling function was called usingcall-interactively.The argument kind should be either the symbol
interactiveor the symbolany. If it isinteractive, thencalled-interactively-preturnstonly if the call was made directly by the user—e.g., if the user typed a key sequence bound to the calling function, but not if the user ran a keyboard macro that called the function (see Keyboard Macros). If kind isany,called-interactively-preturnstfor any kind of interactive call, including keyboard macros.If in doubt, use
any; the only known proper use ofinteractiveis if you need to decide whether to display a helpful message while a function is running.A function is never considered to be called interactively if it was called via Lisp evaluation (or with
applyorfuncall).
Here is an example of using called-interactively-p:
(defun foo ()
(interactive)
(when (called-interactively-p 'any)
(message "Interactive!")
'foo-called-interactively))
;; Type M-x foo.
-| Interactive!
(foo)
=> nil
Here is another example that contrasts direct and indirect calls to
called-interactively-p.
(defun bar ()
(interactive)
(message "%s" (list (foo) (called-interactively-p 'any))))
;; Type M-x bar.
-| (nil t)
The editor command loop sets several Lisp variables to keep status
records for itself and for commands that are run. With the exception of
this-command and last-command it's generally a bad idea to
change any of these variables in a Lisp program.
This variable records the name of the previous command executed by the command loop (the one before the current command). Normally the value is a symbol with a function definition, but this is not guaranteed.
The value is copied from
this-commandwhen a command returns to the command loop, except when the command has specified a prefix argument for the following command.This variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
This variable is set up by Emacs just like
last-command, but never altered by Lisp programs.
This variable stores the most recently executed command that was not part of an input event. This is the command
repeatwill try to repeat, See Repeating.
This variable records the name of the command now being executed by the editor command loop. Like
last-command, it is normally a symbol with a function definition.The command loop sets this variable just before running a command, and copies its value into
last-commandwhen the command finishes (unless the command specified a prefix argument for the following command).Some commands set this variable during their execution, as a flag for whatever command runs next. In particular, the functions for killing text set
this-commandtokill-regionso that any kill commands immediately following will know to append the killed text to the previous kill.
If you do not want a particular command to be recognized as the previous
command in the case where it got an error, you must code that command to
prevent this. One way is to set this-command to t at the
beginning of the command, and set this-command back to its proper
value at the end, like this:
(defun foo (args...)
(interactive ...)
(let ((old-this-command this-command))
(setq this-command t)
...do the work...
(setq this-command old-this-command)))
We do not bind this-command with let because that would
restore the old value in case of error—a feature of let which
in this case does precisely what we want to avoid.
This has the same value as
this-commandexcept when command remapping occurs (see Remapping Commands). In that case,this-commandgives the command actually run (the result of remapping), andthis-original-commandgives the command that was specified to run but remapped into another command.
This function returns a string or vector containing the key sequence that invoked the present command, plus any previous commands that generated the prefix argument for this command. Any events read by the command using
read-eventwithout a timeout get tacked on to the end.However, if the command has called
read-key-sequence, it returns the last read key sequence. See Key Sequence Input. The value is a string if all events in the sequence were characters that fit in a string. See Input Events.(this-command-keys) ;; Now use C-u C-x C-e to evaluate that. => "^U^X^E"
Like
this-command-keys, except that it always returns the events in a vector, so you don't need to deal with the complexities of storing input events in a string (see Strings of Events).
This function empties out the table of events for
this-command-keysto return. Unless keep-record is non-nil, it also empties the records that the functionrecent-keys(see Recording Input) will subsequently return. This is useful after reading a password, to prevent the password from echoing inadvertently as part of the next command in certain cases.
This variable holds the last input event read as part of a key sequence, not counting events resulting from mouse menus.
One use of this variable is for telling
x-popup-menuwhere to pop up a menu. It is also used internally byy-or-n-p(see Yes-or-No Queries).
This variable is set to the last input event that was read by the command loop as part of a command. The principal use of this variable is in
self-insert-command, which uses it to decide which character to insert.last-command-event ;; Now use C-u C-x C-e to evaluate that. => 5The value is 5 because that is the ASCII code for C-e.
This variable records which frame the last input event was directed to. Usually this is the frame that was selected when the event was generated, but if that frame has redirected input focus to another frame, the value is the frame to which the event was redirected. See Input Focus.
If the last event came from a keyboard macro, the value is
macro.
It is not easy to display a value of point in the middle of a
sequence of text that has the display, composition or
is invisible. Therefore, after a command finishes and returns to the
command loop, if point is within such a sequence, the command loop
normally moves point to the edge of the sequence.
A command can inhibit this feature by setting the variable
disable-point-adjustment:
If this variable is non-
nilwhen a command returns to the command loop, then the command loop does not check for those text properties, and does not move point out of sequences that have them.The command loop sets this variable to
nilbefore each command, so if a command sets it, the effect applies only to that command.
If you set this variable to a non-
nilvalue, the feature of moving point out of these sequences is completely turned off.
The Emacs command loop reads a sequence of input events that represent keyboard or mouse activity, or system events sent to Emacs. The events for keyboard activity are characters or symbols; other events are always lists. This section describes the representation and meaning of input events in detail.
This function returns non-
nilif object is an input event or event type.Note that any symbol might be used as an event or an event type.
eventpcannot distinguish whether a symbol is intended by Lisp code to be used as an event. Instead, it distinguishes whether the symbol has actually been used in an event that has been read as input in the current Emacs session. If a symbol has not yet been so used,eventpreturnsnil.
There are two kinds of input you can get from the keyboard: ordinary keys, and function keys. Ordinary keys correspond to characters; the events they generate are represented in Lisp as characters. The event type of a character event is the character itself (an integer); see Classifying Events.
An input character event consists of a basic code between 0 and 524287, plus any or all of these modifier bits:
ascii control characters such as C-a have special basic codes of their own, so Emacs needs no special bit to indicate them. Thus, the code for C-a is just 1.
But if you type a control combination not in ASCII, such as
% with the control key, the numeric value you get is the code
for % plus
2**26
(assuming the terminal supports non-ASCII
control characters).
For letters, the basic code itself indicates upper versus lower case; for digits and punctuation, the shift key selects an entirely different character with a different basic code. In order to keep within the ASCII character set whenever possible, Emacs avoids using the 2**25 bit for those characters.
However, ASCII provides no way to distinguish C-A from
C-a, so Emacs uses the
2**25
bit in C-A and not in
C-a.
It is best to avoid mentioning specific bit numbers in your program.
To test the modifier bits of a character, use the function
event-modifiers (see Classifying Events). When making key
bindings, you can use the read syntax for characters with modifier bits
(`\C-', `\M-', and so on). For making key bindings with
define-key, you can use lists such as (control hyper ?x) to
specify the characters (see Changing Key Bindings). The function
event-convert-list converts such a list into an event type
(see Classifying Events).
Most keyboards also have function keys—keys that have names or
symbols that are not characters. Function keys are represented in
Emacs Lisp as symbols; the symbol's name is the function key's label,
in lower case. For example, pressing a key labeled <F1> generates
an input event represented by the symbol f1.
The event type of a function key event is the event symbol itself. See Classifying Events.
Here are a few special cases in the symbol-naming convention for function keys:
backspace, tab, newline, return, delete
In ASCII, C-i and <TAB> are the same character. If the
terminal can distinguish between them, Emacs conveys the distinction to
Lisp programs by representing the former as the integer 9, and the
latter as the symbol tab.
Most of the time, it's not useful to distinguish the two. So normally
local-function-key-map (see Translation Keymaps) is set up
to map tab into 9. Thus, a key binding for character code 9
(the character C-i) also applies to tab. Likewise for
the other symbols in this group. The function read-char
likewise converts these events into characters.
In ASCII, <BS> is really C-h. But backspace
converts into the character code 127 (<DEL>), not into code 8
(<BS>). This is what most users prefer.
left, up, right, down
kp-add, kp-decimal, kp-divide, ...
kp-0, kp-1, ...
kp-f1, kp-f2, kp-f3, kp-f4
kp-home, kp-left, kp-up, kp-right, kp-down
home, left, ...
kp-prior, kp-next, kp-end, kp-begin, kp-insert, kp-delete
You can use the modifier keys <ALT>, <CTRL>, <HYPER>, <META>, <SHIFT>, and <SUPER> with function keys. The way to represent them is with prefixes in the symbol name:
Thus, the symbol for the key <F3> with <META> held down is
M-f3. When you use more than one prefix, we recommend you
write them in alphabetical order; but the order does not matter in
arguments to the key-binding lookup and modification functions.
Emacs supports four kinds of mouse events: click events, drag events, button-down events, and motion events. All mouse events are represented as lists. The car of the list is the event type; this says which mouse button was involved, and which modifier keys were used with it. The event type can also distinguish double or triple button presses (see Repeat Events). The rest of the list elements give position and time information.
For key lookup, only the event type matters: two events of the same type necessarily run the same command. The command can access the full values of these events using the `e' interactive code. See Interactive Codes.
A key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer. This does not imply that clicking in a window selects that window or its buffer—that is entirely under the control of the command binding of the key sequence.
When the user presses a mouse button and releases it at the same location, that generates a click event. All mouse click event share the same format:
(event-type position click-count)
mouse-1, mouse-2, ..., where the
buttons are numbered left to right.
You can also use prefixes `A-', `C-', `H-', `M-', `S-' and `s-' for modifiers alt, control, hyper, meta, shift and super, just as you would with function keys.
This symbol also serves as the event type of the event. Key bindings
describe events by their types; thus, if there is a key binding for
mouse-1, that binding would apply to all events whose
event-type is mouse-1.
To access the contents of a mouse position list in the position slot of a click event, you should typically use the functions documented in Accessing Mouse. The explicit format of the list depends on where the click occurred. For clicks in the text area, mode line, header line, or in the fringe or marginal areas, the mouse position list has the form
(window pos-or-area (x . y) timestamp
object text-pos (col . row)
image (dx . dy) (width . height))
The meanings of these list elements are as follows:
mode-line,
header-line, vertical-line, left-margin,
right-margin, left-fringe, or right-fringe.
In one special case, pos-or-area is a list containing a symbol
(one of the symbols listed above) instead of just the symbol. This
happens after the imaginary prefix keys for the event are registered
by Emacs. See Key Sequence Input.
(0 . 0) is taken to be
the top left corner of the text area. See Window Sizes. For
clicks in a mode line or header line, the coordinate origin is the top
left corner of the window itself. For fringes, margins, and the
vertical border, x does not have meaningful data. For fringes
and margins, y is relative to the bottom edge of the header
line. In all cases, the x and y coordinates increase
rightward and downward respectively.
nil if there is no string-type text property at the
click position, or a cons cell of the form (string
. string-pos) if there is one:
nil. For other events, it is the buffer position closest to
the click.
nil if there is no image at the position clicked on, or it is
an image object as returned by find-image if click was in an image.
(0 . 0). If
object is nil, the coordinates are relative to the top
left corner of the character glyph clicked on.
nil, those of the character glyph clicked on.
For clicks on a scroll bar, position has this form:
(window area (portion . whole) timestamp part)
vertical-scroll-bar.
0.
0.
0.
handle (the scroll bar handle), above-handle
(the area above the handle), below-handle (the area below the
handle), up (the up arrow at one end of the scroll bar), or
down (the down arrow at one end of the scroll bar).
With Emacs, you can have a drag event without even changing your clothes. A drag event happens every time the user presses a mouse button and then moves the mouse to a different character position before releasing the button. Like all mouse events, drag events are represented in Lisp as lists. The lists record both the starting mouse position and the final position, like this:
(event-type
(window1 START-POSITION)
(window2 END-POSITION))
For a drag event, the name of the symbol event-type contains the
prefix `drag-'. For example, dragging the mouse with button 2
held down generates a drag-mouse-2 event. The second and third
elements of the event give the starting and ending position of the
drag, as mouse position lists (see Click Events). You can access
the second element of any mouse event in the same way. However, the
drag event may end outside the boundaries of the frame that was
initially selected. In that case, the third element's position list
contains that frame in place of a window.
The `drag-' prefix follows the modifier key prefixes such as `C-' and `M-'.
If read-key-sequence receives a drag event that has no key
binding, and the corresponding click event does have a binding, it
changes the drag event into a click event at the drag's starting
position. This means that you don't have to distinguish between click
and drag events unless you want to.
Click and drag events happen when the user releases a mouse button. They cannot happen earlier, because there is no way to distinguish a click from a drag until the button is released.
If you want to take action as soon as a button is pressed, you need to handle button-down events.11 These occur as soon as a button is pressed. They are represented by lists that look exactly like click events (see Click Events), except that the event-type symbol name contains the prefix `down-'. The `down-' prefix follows modifier key prefixes such as `C-' and `M-'.
The function read-key-sequence ignores any button-down events
that don't have command bindings; therefore, the Emacs command loop
ignores them too. This means that you need not worry about defining
button-down events unless you want them to do something. The usual
reason to define a button-down event is so that you can track mouse
motion (by reading motion events) until the button is released.
See Motion Events.
If you press the same mouse button more than once in quick succession without moving the mouse, Emacs generates special repeat mouse events for the second and subsequent presses.
The most common repeat events are double-click events. Emacs generates a double-click event when you click a button twice; the event happens when you release the button (as is normal for all click events).
The event type of a double-click event contains the prefix
`double-'. Thus, a double click on the second mouse button with
<meta> held down comes to the Lisp program as
M-double-mouse-2. If a double-click event has no binding, the
binding of the corresponding ordinary click event is used to execute
it. Thus, you need not pay attention to the double click feature
unless you really want to.
When the user performs a double click, Emacs generates first an ordinary click event, and then a double-click event. Therefore, you must design the command binding of the double click event to assume that the single-click command has already run. It must produce the desired results of a double click, starting from the results of a single click.
This is convenient, if the meaning of a double click somehow builds on the meaning of a single click—which is recommended user interface design practice for double clicks.
If you click a button, then press it down again and start moving the mouse with the button held down, then you get a double-drag event when you ultimately release the button. Its event type contains `double-drag' instead of just `drag'. If a double-drag event has no binding, Emacs looks for an alternate binding as if the event were an ordinary drag.
Before the double-click or double-drag event, Emacs generates a double-down event when the user presses the button down for the second time. Its event type contains `double-down' instead of just `down'. If a double-down event has no binding, Emacs looks for an alternate binding as if the event were an ordinary button-down event. If it finds no binding that way either, the double-down event is ignored.
To summarize, when you click a button and then press it again right away, Emacs generates a down event and a click event for the first click, a double-down event when you press the button again, and finally either a double-click or a double-drag event.
If you click a button twice and then press it again, all in quick succession, Emacs generates a triple-down event, followed by either a triple-click or a triple-drag. The event types of these events contain `triple' instead of `double'. If any triple event has no binding, Emacs uses the binding that it would use for the corresponding double event.
If you click a button three or more times and then press it again, the events for the presses beyond the third are all triple events. Emacs does not have separate event types for quadruple, quintuple, etc. events. However, you can look at the event list to find out precisely how many times the button was pressed.
This function returns the number of consecutive button presses that led up to event. If event is a double-down, double-click or double-drag event, the value is 2. If event is a triple event, the value is 3 or greater. If event is an ordinary mouse event (not a repeat event), the value is 1.
To generate repeat events, successive mouse button presses must be at approximately the same screen position. The value of
double-click-fuzzspecifies the maximum number of pixels the mouse may be moved (horizontally or vertically) between two successive clicks to make a double-click.This variable is also the threshold for motion of the mouse to count as a drag.
To generate repeat events, the number of milliseconds between successive button presses must be less than the value of
double-click-time. Settingdouble-click-timetonildisables multi-click detection entirely. Setting it totremoves the time limit; Emacs then detects multi-clicks by position only.
Emacs sometimes generates mouse motion events to describe motion of the mouse without any button activity. Mouse motion events are represented by lists that look like this:
(mouse-movement POSITION)
position is a mouse position list (see Click Events), specifying the current position of the mouse cursor. As with the end-position of a drag event, this position list may represent a location outside the boundaries of the initially selected frame, in which case the list contains that frame in place of a window.
The special form track-mouse enables generation of motion
events within its body. Outside of track-mouse forms, Emacs
does not generate events for mere motion of the mouse, and these
events do not appear. See Mouse Tracking.
Window systems provide general ways for the user to control which window gets keyboard input. This choice of window is called the focus. When the user does something to switch between Emacs frames, that generates a focus event. The normal definition of a focus event, in the global keymap, is to select a new frame within Emacs, as the user would expect. See Input Focus, which also describes hooks related to focus events.
Focus events are represented in Lisp as lists that look like this:
(switch-frame new-frame)
where new-frame is the frame switched to.
Some X window managers are set up so that just moving the mouse into a window is enough to set the focus there. Usually, there is no need for a Lisp program to know about the focus change until some other kind of input arrives. Emacs generates a focus event only when the user actually types a keyboard key or presses a mouse button in the new frame; just moving the mouse between frames does not generate a focus event.
A focus event in the middle of a key sequence would garble the sequence. So Emacs never generates a focus event in the middle of a key sequence. If the user changes focus in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that the focus event comes either before or after the multi-event key sequence, and not within it.
A few other event types represent occurrences within the system.
(delete-frame (frame))
The standard definition of the delete-frame event is to delete frame.
(iconify-frame (frame))
ignore; since the
frame has already been iconified, Emacs has no work to do. The purpose
of this event type is so that you can keep track of such events if you
want to.
(make-frame-visible (frame))
ignore; since the
frame has already been made visible, Emacs has no work to do.
(wheel-up position)(wheel-down position)
This kind of event is generated only on some kinds of systems. On some
systems, mouse-4 and mouse-5 are used instead. For
portable code, use the variables mouse-wheel-up-event and
mouse-wheel-down-event defined in mwheel.el to determine
what event types to expect for the mouse wheel.
(drag-n-drop position files)
The element position is a list describing the position of the event, in the same format as used in a mouse-click event (see Click Events), and files is the list of file names that were dragged and dropped. The usual way to handle this event is by visiting these files.
This kind of event is generated, at present, only on some kinds of systems.
help-echohelp-echo text property.
The generated event has this form:
(help-echo frame help window object pos)
The precise meaning of the event parameters and the way these parameters are used to display the help-echo text are described in Text help-echo.
sigusr1sigusr2SIGUSR1 and SIGUSR2. They contain no
additional data because signals do not carry additional information.
They can be useful for debugging (see Error Debugging).
To catch a user signal, bind the corresponding event to an interactive
command in the special-event-map (see Active Keymaps).
The command is called with no arguments, and the specific signal event is
available in last-input-event. For example:
(defun sigusr-handler ()
(interactive)
(message "Caught signal %S" last-input-event))
(define-key special-event-map [sigusr1] 'sigusr-handler)
To test the signal handler, you can make Emacs send a signal to itself:
(signal-process (emacs-pid) 'sigusr1)
language-change (language-change frame codepage language-id)
Here frame is the frame which was current when the input
language changed; codepage is the new codepage number; and
language-id is the numerical ID of the new input language. The
coding-system (see Coding Systems) that corresponds to
codepage is cpcodepage or
windows-codepage. To convert language-id to a
string (e.g., to use it for various language-dependent features, such
as set-language-environment), use the
w32-get-locale-info function, like this:
;; Get the abbreviated language name, such as "ENU" for English
(w32-get-locale-info language-id)
;; Get the full English name of the language,
;; such as "English (United States)"
(w32-get-locale-info language-id 4097)
;; Get the full localized name of the language
(w32-get-locale-info language-id t)
If one of these events arrives in the middle of a key sequence—that is, after a prefix key—then Emacs reorders the events so that this event comes either before or after the multi-event key sequence, not within it.
If the user presses and releases the left mouse button over the same location, that generates a sequence of events like this:
(down-mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864320))
(mouse-1 (#<window 18 on NEWS> 2613 (0 . 38) -864180))
While holding the control key down, the user might hold down the second mouse button, and drag the mouse from one line to the next. That produces two events, as shown here:
(C-down-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219))
(C-drag-mouse-2 (#<window 18 on NEWS> 3440 (0 . 27) -731219)
(#<window 18 on NEWS> 3510 (0 . 28) -729648))
While holding down the meta and shift keys, the user might press the second mouse button on the window's mode line, and then drag the mouse into another window. That produces a pair of events like these:
(M-S-down-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844))
(M-S-drag-mouse-2 (#<window 18 on NEWS> mode-line (33 . 31) -457844)
(#<window 20 on carlton-sanskrit.tex> 161 (33 . 3)
-453816))
The frame with input focus might not take up the entire screen, and
the user might move the mouse outside the scope of the frame. Inside
the track-mouse special form, that produces an event like this:
(mouse-movement (#<frame *ielm* 0x102849a30> nil (563 . 205) 532301936))
To handle a SIGUSR1 signal, define an interactive function, and
bind it to the signal usr1 event sequence:
(defun usr1-handler ()
(interactive)
(message "Got USR1 signal"))
(global-set-key [signal usr1] 'usr1-handler)
Every event has an event type, which classifies the event for key binding purposes. For a keyboard event, the event type equals the event value; thus, the event type for a character is the character, and the event type for a function key symbol is the symbol itself. For events that are lists, the event type is the symbol in the car of the list. Thus, the event type is always a symbol or a character.
Two events of the same type are equivalent where key bindings are concerned; thus, they always run the same command. That does not necessarily mean they do the same things, however, as some commands look at the whole event to decide what to do. For example, some commands use the location of a mouse event to decide where in the buffer to act.
Sometimes broader classifications of events are useful. For example, you might want to ask whether an event involved the <META> key, regardless of which other key or mouse button was used.
The functions event-modifiers and event-basic-type are
provided to get such information conveniently.
This function returns a list of the modifiers that event has. The modifiers are symbols; they include
shift,control,meta,alt,hyperandsuper. In addition, the modifiers list of a mouse event symbol always contains one ofclick,drag, anddown. For double or triple events, it also containsdoubleortriple.The argument event may be an entire event object, or just an event type. If event is a symbol that has never been used in an event that has been read as input in the current Emacs session, then
event-modifierscan returnnil, even when event actually has modifiers.Here are some examples:
(event-modifiers ?a) => nil (event-modifiers ?A) => (shift) (event-modifiers ?\C-a) => (control) (event-modifiers ?\C-%) => (control) (event-modifiers ?\C-\S-a) => (control shift) (event-modifiers 'f5) => nil (event-modifiers 's-f5) => (super) (event-modifiers 'M-S-f5) => (meta shift) (event-modifiers 'mouse-1) => (click) (event-modifiers 'down-mouse-1) => (down)The modifiers list for a click event explicitly contains
click, but the event symbol name itself does not contain `click'.
This function returns the key or mouse button that event describes, with all modifiers removed. The event argument is as in
event-modifiers. For example:(event-basic-type ?a) => 97 (event-basic-type ?A) => 97 (event-basic-type ?\C-a) => 97 (event-basic-type ?\C-\S-a) => 97 (event-basic-type 'f5) => f5 (event-basic-type 's-f5) => f5 (event-basic-type 'M-S-f5) => f5 (event-basic-type 'down-mouse-1) => mouse-1
This function returns non-
nilif object is a mouse movement event.
This function converts a list of modifier names and a basic event type to an event type which specifies all of them. The basic event type must be the last element of the list. For example,
(event-convert-list '(control ?a)) => 1 (event-convert-list '(control meta ?a)) => -134217727 (event-convert-list '(control super f1)) => C-s-f1
This section describes convenient functions for accessing the data in
a mouse button or motion event. Keyboard event data can be accessed
using the same functions, but data elements that aren't applicable to
keyboard events are zero or nil.
The following two functions return a mouse position list (see Click Events), specifying the position of a mouse event.
This returns the starting position of event.
If event is a click or button-down event, this returns the location of the event. If event is a drag event, this returns the drag's starting position.
This returns the ending position of event.
If event is a drag event, this returns the position where the user released the mouse button. If event is a click or button-down event, the value is actually the starting position, which is the only position such events have.
This function returns non-
nilif object is a mouse position list, in either of the formats documented in Click Events); andnilotherwise.
These functions take a mouse position list as argument, and return various parts of it:
Return the window that position is in. If position represents a location outside the frame where the event was initiated, return that frame instead.
Return the window area recorded in position. It returns
nilwhen the event occurred in the text area of the window; otherwise, it is a symbol identifying the area in which the event occurred.
Return the buffer position in position. When the event occurred in the text area of the window, in a marginal area, or on a fringe, this is an integer specifying a buffer position. Otherwise, the value is undefined.
Return the pixel-based x and y coordinates in position, as a cons cell
(x.y). These coordinates are relative to the window given byposn-window.This example shows how to convert the window-relative coordinates in the text area of a window into frame-relative coordinates:
(defun frame-relative-coordinates (position) "Return frame-relative coordinates from POSITION. POSITION is assumed to lie in a window text area." (let* ((x-y (posn-x-y position)) (window (posn-window position)) (edges (window-inside-pixel-edges window))) (cons (+ (car x-y) (car edges)) (+ (cdr x-y) (cadr edges)))))
This function returns a cons cell
(col.row), containing the estimated column and row corresponding to buffer position in position. The return value is given in units of the frame's default character width and default line height (including spacing), as computed from the x and y values corresponding to position. (So, if the actual characters have non-default sizes, the actual row and column may differ from these computed values.)Note that row is counted from the top of the text area. If the window given by position possesses a header line (see Header Lines), it is not included in the row count.
Return the actual row and column in position, as a cons cell
(col.row). The values are the actual row and column numbers in the window given by position. See Click Events, for details. The function returnsnilif position does not include actual position values; in that caseposn-col-rowcan be used to get approximate values.Note that this function doesn't account for the visual width of characters on display, like the number of visual columns taken by a tab character or an image. If you need the coordinates in canonical character units, use
posn-col-rowinstead.
Return the string object in position, either
nil, or a cons cell(string.string-pos).
Return the image object in position, either
nil, or an image(image ...).
Return the image or string object in position, either
nil, an image(image ...), or a cons cell(string.string-pos).
Return the pixel-based x and y coordinates relative to the upper left corner of the object in position as a cons cell
(dx.dy). If the position is on buffer text, return the relative position of the buffer-text character closest to that position.
Return the pixel width and height of the object in position as a cons cell
(width.height). If the position is a buffer position, return the size of the character at that position.
Return the timestamp in position. This is the time at which the event occurred, in milliseconds.
These functions compute a position list given particular buffer position or screen position. You can access the data in this position list with the functions described above.
This function returns a position list for position pos in window. pos defaults to point in window; window defaults to the selected window.
posn-at-pointreturnsnilif pos is not visible in window.
This function returns position information corresponding to pixel coordinates x and y in a specified frame or window, frame-or-window, which defaults to the selected window. The coordinates x and y are relative to the frame or window used. If whole is
nil, the coordinates are relative to the window text area, otherwise they are relative to the entire window area including scroll bars, margins and fringes.
These functions are useful for decoding scroll bar events.
This function returns the fractional vertical position of a scroll bar event within the scroll bar. The value is a cons cell
(portion.whole)containing two integers whose ratio is the fractional position.
This function multiplies (in effect) ratio by total, rounding the result to an integer. The argument ratio is not a number, but rather a pair
(num.denom)—typically a value returned byscroll-bar-event-ratio.This function is handy for scaling a position on a scroll bar into a buffer position. Here's how to do that:
(+ (point-min) (scroll-bar-scale (posn-x-y (event-start event)) (- (point-max) (point-min))))Recall that scroll bar events have two integers forming a ratio, in place of a pair of x and y coordinates.
In most of the places where strings are used, we conceptualize the string as containing text characters—the same kind of characters found in buffers or files. Occasionally Lisp programs use strings that conceptually contain keyboard characters; for example, they may be key sequences or keyboard macro definitions. However, storing keyboard characters in a string is a complex matter, for reasons of historical compatibility, and it is not always possible.
We recommend that new programs avoid dealing with these complexities by not storing keyboard events in strings. Here is how to do that:
lookup-key and
define-key. For example, you can use
read-key-sequence-vector instead of read-key-sequence, and
this-command-keys-vector instead of this-command-keys.
define-key.
listify-key-sequence (see Event Input Misc)
first, to convert it to a list.
The complexities stem from the modifier bits that keyboard input characters can include. Aside from the Meta modifier, none of these modifier bits can be included in a string, and the Meta modifier is allowed only in special cases.
The earliest GNU Emacs versions represented meta characters as codes
in the range of 128 to 255. At that time, the basic character codes
ranged from 0 to 127, so all keyboard character codes did fit in a
string. Many Lisp programs used `\M-' in string constants to stand
for meta characters, especially in arguments to define-key and
similar functions, and key sequences and sequences of events were always
represented as strings.
When we added support for larger basic character codes beyond 127, and additional modifier bits, we had to change the representation of meta characters. Now the flag that represents the Meta modifier in a character is 2**27 and such numbers cannot be included in a string.
To support programs with `\M-' in string constants, there are special rules for including certain meta characters in a string. Here are the rules for interpreting a string as a sequence of input characters:
Functions such as read-key-sequence that construct strings of
keyboard input characters follow these rules: they construct vectors
instead of strings, when the events won't fit in a string.
When you use the read syntax `\M-' in a string, it produces a code in the range of 128 to 255—the same code that you get if you modify the corresponding keyboard event to put it in the string. Thus, meta events in strings work consistently regardless of how they get into the strings.
However, most programs would do well to avoid these issues by following the recommendations at the beginning of this section.
The editor command loop reads key sequences using the function
read-key-sequence, which uses read-event. These and other
functions for event input are also available for use in Lisp programs.
See also momentary-string-display in Temporary Displays,
and sit-for in Waiting. See Terminal Input, for
functions and variables for controlling terminal input modes and
debugging terminal input.
For higher-level input facilities, see Minibuffers.
The command loop reads input a key sequence at a time, by calling
read-key-sequence. Lisp programs can also call this function;
for example, describe-key uses it to read the key to describe.
This function reads a key sequence and returns it as a string or vector. It keeps reading events until it has accumulated a complete key sequence; that is, enough to specify a non-prefix command using the currently active keymaps. (Remember that a key sequence that starts with a mouse event is read using the keymaps of the buffer in the window that the mouse was in, not the current buffer.)
If the events are all characters and all can fit in a string, then
read-key-sequencereturns a string (see Strings of Events). Otherwise, it returns a vector, since a vector can hold all kinds of events—characters, symbols, and lists. The elements of the string or vector are the events in the key sequence.Reading a key sequence includes translating the events in various ways. See Translation Keymaps.
The argument prompt is either a string to be displayed in the echo area as a prompt, or
nil, meaning not to display a prompt. The argument continue-echo, if non-nil, means to echo this key as a continuation of the previous key.Normally any upper case event is converted to lower case if the original event is undefined and the lower case equivalent is defined. The argument dont-downcase-last, if non-
nil, means do not convert the last event to lower case. This is appropriate for reading a key sequence to be defined.The argument switch-frame-ok, if non-
nil, means that this function should process aswitch-frameevent if the user switches frames before typing anything. If the user switches frames in the middle of a key sequence, or at the start of the sequence but switch-frame-ok isnil, then the event will be put off until after the current key sequence.The argument command-loop, if non-
nil, means that this key sequence is being read by something that will read commands one after another. It should benilif the caller will read just one key sequence.In the following example, Emacs displays the prompt `?' in the echo area, and then the user types C-x C-f.
(read-key-sequence "?") ---------- Echo Area ---------- ?C-x C-f ---------- Echo Area ---------- => "^X^F"The function
read-key-sequencesuppresses quitting: C-g typed while reading with this function works like any other character, and does not setquit-flag. See Quitting.
This is like
read-key-sequenceexcept that it always returns the key sequence as a vector, never as a string. See Strings of Events.
If an input character is upper-case (or has the shift modifier) and
has no key binding, but its lower-case equivalent has one, then
read-key-sequence converts the character to lower case. Note
that lookup-key does not perform case conversion in this way.
When reading input results in such a shift-translation, Emacs
sets the variable this-command-keys-shift-translated to a
non-nil value. Lisp programs can examine this variable if they
need to modify their behavior when invoked by shift-translated keys.
For example, the function handle-shift-selection examines the
value of this variable to determine how to activate or deactivate the
region (see handle-shift-selection).
The function read-key-sequence also transforms some mouse events.
It converts unbound drag events into click events, and discards unbound
button-down events entirely. It also reshuffles focus events and
miscellaneous window events so that they never appear in a key sequence
with any other events.
When mouse events occur in special parts of a window, such as a mode
line or a scroll bar, the event type shows nothing special—it is the
same symbol that would normally represent that combination of mouse
button and modifier keys. The information about the window part is kept
elsewhere in the event—in the coordinates. But
read-key-sequence translates this information into imaginary
prefix keys, all of which are symbols: header-line,
horizontal-scroll-bar, menu-bar, mode-line,
vertical-line, and vertical-scroll-bar. You can define
meanings for mouse clicks in special window parts by defining key
sequences using these imaginary prefix keys.
For example, if you call read-key-sequence and then click the
mouse on the window's mode line, you get two events, like this:
(read-key-sequence "Click on the mode line: ")
=> [mode-line
(mouse-1
(#<window 6 on NEWS> mode-line
(40 . 63) 5959987))]
This variable's value is the number of key sequences processed so far in this Emacs session. This includes key sequences read from the terminal and key sequences read from keyboard macros being executed.
The lowest level functions for command input are read-event,
read-char, and read-char-exclusive.
This function reads and returns the next event of command input, waiting if necessary until an event is available.
The returned event may come directly from the user, or from a keyboard macro. It is not decoded by the keyboard's input coding system (see Terminal I/O Encoding).
If the optional argument prompt is non-
nil, it should be a string to display in the echo area as a prompt. Otherwise,read-eventdoes not display any message to indicate it is waiting for input; instead, it prompts by echoing: it displays descriptions of the events that led to or were read by the current command. See The Echo Area.If inherit-input-method is non-
nil, then the current input method (if any) is employed to make it possible to enter a non-ASCII character. Otherwise, input method handling is disabled for reading this event.If
cursor-in-echo-areais non-nil, thenread-eventmoves the cursor temporarily to the echo area, to the end of any message displayed there. Otherwiseread-eventdoes not move the cursor.If seconds is non-
nil, it should be a number specifying the maximum time to wait for input, in seconds. If no input arrives within that time,read-eventstops waiting and returnsnil. A floating point seconds means to wait for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down. If seconds isnil,read-eventwaits as long as necessary for input to arrive.If seconds is
nil, Emacs is considered idle while waiting for user input to arrive. Idle timers—those created withrun-with-idle-timer(see Idle Timers)—can run during this period. However, if seconds is non-nil, the state of idleness remains unchanged. If Emacs is non-idle whenread-eventis called, it remains non-idle throughout the operation ofread-event; if Emacs is idle (which can happen if the call happens inside an idle timer), it remains idle.If
read-eventgets an event that is defined as a help character, then in some casesread-eventprocesses the event directly without returning. See Help Functions. Certain other events, called special events, are also processed directly withinread-event(see Special Events).Here is what happens if you call
read-eventand then press the right-arrow function key:(read-event) => right
This function reads and returns a character of command input. If the user generates an event which is not a character (i.e., a mouse click or function key event),
read-charsignals an error. The arguments work as inread-event.In the first example, the user types the character 1 (ASCII code 49). The second example shows a keyboard macro definition that calls
read-charfrom the minibuffer usingeval-expression.read-charreads the keyboard macro's very next character, which is 1. Theneval-expressiondisplays its return value in the echo area.(read-char) => 49 ;; We assume here you use M-: to evaluate this. (symbol-function 'foo) => "^[:(read-char)^M1" (execute-kbd-macro 'foo) -| 49 => nil
This function reads and returns a character of command input. If the user generates an event which is not a character,
read-char-exclusiveignores it and reads another event, until it gets a character. The arguments work as inread-event.
None of the above functions suppress quitting.
This variable holds the total number of input events received so far from the terminal—not counting those generated by keyboard macros.
We emphasize that, unlike read-key-sequence, the functions
read-event, read-char, and read-char-exclusive do
not perform the translations described in Translation Keymaps.
If you wish to read a single key taking these translations into
account, use the function read-key:
This function reads a single key. It is intermediate between
read-key-sequenceandread-event. Unlike the former, it reads a single key, not a key sequence. Unlike the latter, it does not return a raw event, but decodes and translates the user input according toinput-decode-map,local-function-key-map, andkey-translation-map(see Translation Keymaps).The argument prompt is either a string to be displayed in the echo area as a prompt, or
nil, meaning not to display a prompt.
This function uses
read-keyto read and return a single character. It ignores any input that is not a member of chars, a list of accepted characters. Optionally, it will also ignore keyboard-quit events while it is waiting for valid input. If you bindhelp-form(see Help Functions) to a non-nilvalue while callingread-char-choice, then pressinghelp-charcauses it to evaluatehelp-formand display the result. It then continues to wait for a valid input character, or keyboard-quit.
Emacs modifies every event it reads according to
extra-keyboard-modifiers, then translates it through
keyboard-translate-table (if applicable), before returning it
from read-event.
This variable lets Lisp programs “press” the modifier keys on the keyboard. The value is a character. Only the modifiers of the character matter. Each time the user types a keyboard key, it is altered as if those modifier keys were held down. For instance, if you bind
extra-keyboard-modifiersto?\C-\M-a, then all keyboard input characters typed during the scope of the binding will have the control and meta modifiers applied to them. The character?\C-@, equivalent to the integer 0, does not count as a control character for this purpose, but as a character with no modifiers. Thus, settingextra-keyboard-modifiersto zero cancels any modification.When using a window system, the program can press any of the modifier keys in this way. Otherwise, only the <CTL> and <META> keys can be virtually pressed.
Note that this variable applies only to events that really come from the keyboard, and has no effect on mouse events or any other events.
This terminal-local variable is the translate table for keyboard characters. It lets you reshuffle the keys on the keyboard without changing any command bindings. Its value is normally a char-table, or else
nil. (It can also be a string or vector, but this is considered obsolete.)If
keyboard-translate-tableis a char-table (see Char-Tables), then each character read from the keyboard is looked up in this char-table. If the value found there is non-nil, then it is used instead of the actual input character.Note that this translation is the first thing that happens to a character after it is read from the terminal. Record-keeping features such as
recent-keysand dribble files record the characters after translation.Note also that this translation is done before the characters are supplied to input methods (see Input Methods). Use
translation-table-for-input(see Translation of Characters), if you want to translate characters after input methods operate.
This function modifies
keyboard-translate-tableto translate character code from into character code to. It creates the keyboard translate table if necessary.
Here's an example of using the keyboard-translate-table to
make C-x, C-c and C-v perform the cut, copy and paste
operations:
(keyboard-translate ?\C-x 'control-x)
(keyboard-translate ?\C-c 'control-c)
(keyboard-translate ?\C-v 'control-v)
(global-set-key [control-x] 'kill-region)
(global-set-key [control-c] 'kill-ring-save)
(global-set-key [control-v] 'yank)
On a graphical terminal that supports extended ASCII input, you can still get the standard Emacs meanings of one of those characters by typing it with the shift key. That makes it a different character as far as keyboard translation is concerned, but it has the same usual meaning.
See Translation Keymaps, for mechanisms that translate event sequences
at the level of read-key-sequence.
The event-reading functions invoke the current input method, if any
(see Input Methods). If the value of input-method-function
is non-nil, it should be a function; when read-event reads
a printing character (including <SPC>) with no modifier bits, it
calls that function, passing the character as an argument.
If this is non-
nil, its value specifies the current input method function.Warning: don't bind this variable with
let. It is often buffer-local, and if you bind it around reading input (which is exactly when you would bind it), switching buffers asynchronously while Emacs is waiting will cause the value to be restored in the wrong buffer.
The input method function should return a list of events which should
be used as input. (If the list is nil, that means there is no
input, so read-event waits for another event.) These events are
processed before the events in unread-command-events
(see Event Input Misc). Events
returned by the input method function are not passed to the input method
function again, even if they are printing characters with no modifier
bits.
If the input method function calls read-event or
read-key-sequence, it should bind input-method-function to
nil first, to prevent recursion.
The input method function is not called when reading the second and
subsequent events of a key sequence. Thus, these characters are not
subject to input method processing. The input method function should
test the values of overriding-local-map and
overriding-terminal-local-map; if either of these variables is
non-nil, the input method should put its argument into a list and
return that list with no further processing.
You can use the function read-quoted-char to ask the user to
specify a character, and allow the user to specify a control or meta
character conveniently, either literally or as an octal character code.
The command quoted-insert uses this function.
This function is like
read-char, except that if the first character read is an octal digit (0–7), it reads any number of octal digits (but stopping if a non-octal digit is found), and returns the character represented by that numeric character code. If the character that terminates the sequence of octal digits is <RET>, it is discarded. Any other terminating character is used as input after this function returns.Quitting is suppressed when the first character is read, so that the user can enter a C-g. See Quitting.
If prompt is supplied, it specifies a string for prompting the user. The prompt string is always displayed in the echo area, followed by a single `-'.
In the following example, the user types in the octal number 177 (which is 127 in decimal).
(read-quoted-char "What character") ---------- Echo Area ---------- What character 1 7 7- ---------- Echo Area ---------- => 127
This section describes how to peek ahead at events without using
them up, how to check for pending input, and how to discard pending
input. See also the function read-passwd (see Reading a Password).
This variable holds a list of events waiting to be read as command input. The events are used in the order they appear in the list, and removed one by one as they are used.
The variable is needed because in some cases a function reads an event and then decides not to use it. Storing the event in this variable causes it to be processed normally, by the command loop or by the functions to read command input.
For example, the function that implements numeric prefix arguments reads any number of digits. When it finds a non-digit event, it must unread the event so that it can be read normally by the command loop. Likewise, incremental search uses this feature to unread events with no special meaning in a search, because these events should exit the search and then execute normally.
The reliable and easy way to extract events from a key sequence so as to put them in
unread-command-eventsis to uselistify-key-sequence(see below).Normally you add events to the front of this list, so that the events most recently unread will be reread first.
Events read from this list are not normally added to the current command's key sequence (as returned by, e.g.,
this-command-keys), as the events will already have been added once as they were read for the first time. An element of the form(t .event)forces event to be added to the current command's key sequence.
This function converts the string or vector key to a list of individual events, which you can put in
unread-command-events.
This function determines whether any command input is currently available to be read. It returns immediately, with value
tif there is available input,nilotherwise. On rare occasions it may returntwhen no input is available.If the optional argument check-timers is non-
nil, then if no input is available, Emacs runs any timers which are ready. See Timers.
This variable records the last terminal input event read, whether as part of a command or explicitly by a Lisp program.
In the example below, the Lisp program reads the character 1, ASCII code 49. It becomes the value of
last-input-event, while C-e (we assume C-x C-e command is used to evaluate this expression) remains the value oflast-command-event.(progn (print (read-char)) (print last-command-event) last-input-event) -| 49 -| 5 => 49
This construct runs the body forms and returns the value of the last one—but only if no input arrives. If any input arrives during the execution of the body forms, it aborts them (working much like a quit). The
while-no-inputform returnsnilif aborted by a real quit, and returnstif aborted by arrival of other input.If a part of body binds
inhibit-quitto non-nil, arrival of input during those parts won't cause an abort until the end of that part.If you want to be able to distinguish all possible values computed by body from both kinds of abort conditions, write the code like this:
(while-no-input (list (progn . body)))
This function discards the contents of the terminal input buffer and cancels any keyboard macro that might be in the process of definition. It returns
nil.In the following example, the user may type a number of characters right after starting the evaluation of the form. After the
sleep-forfinishes sleeping,discard-inputdiscards any characters typed during the sleep.(progn (sleep-for 2) (discard-input)) => nil
Certain special events are handled at a very low level—as soon
as they are read. The read-event function processes these
events itself, and never returns them. Instead, it keeps waiting for
the first event that is not special and returns that one.
Special events do not echo, they are never grouped into key
sequences, and they never appear in the value of
last-command-event or (this-command-keys). They do not
discard a numeric argument, they cannot be unread with
unread-command-events, they may not appear in a keyboard macro,
and they are not recorded in a keyboard macro while you are defining
one.
Special events do, however, appear in last-input-event
immediately after they are read, and this is the way for the event's
definition to find the actual event.
The events types iconify-frame, make-frame-visible,
delete-frame, drag-n-drop, language-change, and
user signals like sigusr1 are normally handled in this way.
The keymap which defines how to handle special events—and which
events are special—is in the variable special-event-map
(see Active Keymaps).
The wait functions are designed to wait for a certain amount of time
to pass or until there is input. For example, you may wish to pause in
the middle of a computation to allow the user time to view the display.
sit-for pauses and updates the screen, and returns immediately if
input comes in, while sleep-for pauses without updating the
screen.
This function performs redisplay (provided there is no pending input from the user), then waits seconds seconds, or until input is available. The usual purpose of
sit-foris to give the user time to read text that you display. The value istifsit-forwaited the full time with no input arriving (see Event Input Misc). Otherwise, the value isnil.The argument seconds need not be an integer. If it is floating point,
sit-forwaits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The expression
(sit-for 0)is equivalent to(redisplay), i.e., it requests a redisplay, without any delay, if there is no pending input. See Forcing Redisplay.If nodisp is non-
nil, thensit-fordoes not redisplay, but it still returns as soon as input is available (or when the timeout elapses).In batch mode (see Batch Mode),
sit-forcannot be interrupted, even by input from the standard input descriptor. It is thus equivalent tosleep-for, which is described below.It is also possible to call
sit-forwith three arguments, as(sit-forseconds millisec nodisp), but that is considered obsolete.
This function simply pauses for seconds seconds without updating the display. It pays no attention to available input. It returns
nil.The argument seconds need not be an integer. If it is floating point,
sleep-forwaits for a fractional number of seconds. Some systems support only a whole number of seconds; on these systems, seconds is rounded down.The optional argument millisec specifies an additional waiting period measured in milliseconds. This adds to the period specified by seconds. If the system doesn't support waiting fractions of a second, you get an error if you specify nonzero millisec.
Use
sleep-forwhen you wish to guarantee a delay.
See Time of Day, for functions to get the current time.
Typing C-g while a Lisp function is running causes Emacs to quit whatever it is doing. This means that control returns to the innermost active command loop.
Typing C-g while the command loop is waiting for keyboard input
does not cause a quit; it acts as an ordinary input character. In the
simplest case, you cannot tell the difference, because C-g
normally runs the command keyboard-quit, whose effect is to quit.
However, when C-g follows a prefix key, they combine to form an
undefined key. The effect is to cancel the prefix key as well as any
prefix argument.
In the minibuffer, C-g has a different definition: it aborts out of the minibuffer. This means, in effect, that it exits the minibuffer and then quits. (Simply quitting would return to the command loop within the minibuffer.) The reason why C-g does not quit directly when the command reader is reading input is so that its meaning can be redefined in the minibuffer in this way. C-g following a prefix key is not redefined in the minibuffer, and it has its normal effect of canceling the prefix key and prefix argument. This too would not be possible if C-g always quit directly.
When C-g does directly quit, it does so by setting the variable
quit-flag to t. Emacs checks this variable at appropriate
times and quits if it is not nil. Setting quit-flag
non-nil in any way thus causes a quit.
At the level of C code, quitting cannot happen just anywhere; only at the
special places that check quit-flag. The reason for this is
that quitting at other places might leave an inconsistency in Emacs's
internal state. Because quitting is delayed until a safe place, quitting
cannot make Emacs crash.
Certain functions such as read-key-sequence or
read-quoted-char prevent quitting entirely even though they wait
for input. Instead of quitting, C-g serves as the requested
input. In the case of read-key-sequence, this serves to bring
about the special behavior of C-g in the command loop. In the
case of read-quoted-char, this is so that C-q can be used
to quote a C-g.
You can prevent quitting for a portion of a Lisp function by binding
the variable inhibit-quit to a non-nil value. Then,
although C-g still sets quit-flag to t as usual, the
usual result of this—a quit—is prevented. Eventually,
inhibit-quit will become nil again, such as when its
binding is unwound at the end of a let form. At that time, if
quit-flag is still non-nil, the requested quit happens
immediately. This behavior is ideal when you wish to make sure that
quitting does not happen within a critical section of the program.
In some functions (such as read-quoted-char), C-g is
handled in a special way that does not involve quitting. This is done
by reading the input with inhibit-quit bound to t, and
setting quit-flag to nil before inhibit-quit
becomes nil again. This excerpt from the definition of
read-quoted-char shows how this is done; it also shows that
normal quitting is permitted after the first character of input.
(defun read-quoted-char (&optional prompt)
"...documentation..."
(let ((message-log-max nil) done (first t) (code 0) char)
(while (not done)
(let ((inhibit-quit first)
...)
(and prompt (message "%s-" prompt))
(setq char (read-event))
(if inhibit-quit (setq quit-flag nil)))
...set the variable code...)
code))
If this variable is non-
nil, then Emacs quits immediately, unlessinhibit-quitis non-nil. Typing C-g ordinarily setsquit-flagnon-nil, regardless ofinhibit-quit.
This variable determines whether Emacs should quit when
quit-flagis set to a value other thannil. Ifinhibit-quitis non-nil, thenquit-flaghas no special effect.
This macro executes body forms in sequence, but allows quitting, at least locally, within body even if
inhibit-quitwas non-niloutside this construct. It returns the value of the last form in body, unless exited by quitting, in which case it returnsnil.If
inhibit-quitisnilon entry towith-local-quit, it only executes the body, and settingquit-flagcauses a normal quit. However, ifinhibit-quitis non-nilso that ordinary quitting is delayed, a non-nilquit-flagtriggers a special kind of local quit. This ends the execution of body and exits thewith-local-quitbody withquit-flagstill non-nil, so that another (ordinary) quit will happen as soon as that is allowed. Ifquit-flagis already non-nilat the beginning of body, the local quit happens immediately and the body doesn't execute at all.This macro is mainly useful in functions that can be called from timers, process filters, process sentinels,
pre-command-hook,post-command-hook, and other places whereinhibit-quitis normally bound tot.
This function signals the
quitcondition with(signal 'quit nil). This is the same thing that quitting does. (Seesignalin Errors.)
You can specify a character other than C-g to use for quitting.
See the function set-input-mode in Input Modes.
Most Emacs commands can use a prefix argument, a number
specified before the command itself. (Don't confuse prefix arguments
with prefix keys.) The prefix argument is at all times represented by a
value, which may be nil, meaning there is currently no prefix
argument. Each command may use the prefix argument or ignore it.
There are two representations of the prefix argument: raw and numeric. The editor command loop uses the raw representation internally, and so do the Lisp variables that store the information, but commands can request either representation.
Here are the possible values of a raw prefix argument:
nil, meaning there is no prefix argument. Its numeric value is
1, but numerous commands make a distinction between nil and the
integer 1.
-. This indicates that M-- or C-u - was
typed, without following digits. The equivalent numeric value is
−1, but some commands make a distinction between the integer
−1 and the symbol -.
We illustrate these possibilities by calling the following function with various prefixes:
(defun display-prefix (arg)
"Display the value of the raw prefix arg."
(interactive "P")
(message "%s" arg))
Here are the results of calling display-prefix with various
raw prefix arguments:
M-x display-prefix -| nil
C-u M-x display-prefix -| (4)
C-u C-u M-x display-prefix -| (16)
C-u 3 M-x display-prefix -| 3
M-3 M-x display-prefix -| 3 ; (Same as C-u 3.)
C-u - M-x display-prefix -| -
M-- M-x display-prefix -| - ; (Same as C-u -.)
C-u - 7 M-x display-prefix -| -7
M-- 7 M-x display-prefix -| -7 ; (Same as C-u -7.)
Emacs uses two variables to store the prefix argument:
prefix-arg and current-prefix-arg. Commands such as
universal-argument that set up prefix arguments for other
commands store them in prefix-arg. In contrast,
current-prefix-arg conveys the prefix argument to the current
command, so setting it has no effect on the prefix arguments for future
commands.
Normally, commands specify which representation to use for the prefix
argument, either numeric or raw, in the interactive specification.
(See Using Interactive.) Alternatively, functions may look at the
value of the prefix argument directly in the variable
current-prefix-arg, but this is less clean.
This function returns the numeric meaning of a valid raw prefix argument value, arg. The argument may be a symbol, a number, or a list. If it is
nil, the value 1 is returned; if it is-, the value −1 is returned; if it is a number, that number is returned; if it is a list, the car of that list (which should be a number) is returned.
This variable holds the raw prefix argument for the current command. Commands may examine it directly, but the usual method for accessing it is with
(interactive "P").
The value of this variable is the raw prefix argument for the next editing command. Commands such as
universal-argumentthat specify prefix arguments for the following command work by setting this variable.
The following commands exist to set up prefix arguments for the following command. Do not call them for any other reason.
This command reads input and specifies a prefix argument for the following command. Don't call this command yourself unless you know what you are doing.
This command adds to the prefix argument for the following command. The argument arg is the raw prefix argument as it was before this command; it is used to compute the updated prefix argument. Don't call this command yourself unless you know what you are doing.
This command adds to the numeric argument for the next command. The argument arg is the raw prefix argument as it was before this command; its value is negated to form the new prefix argument. Don't call this command yourself unless you know what you are doing.
The Emacs command loop is entered automatically when Emacs starts up. This top-level invocation of the command loop never exits; it keeps running as long as Emacs does. Lisp programs can also invoke the command loop. Since this makes more than one activation of the command loop, we call it recursive editing. A recursive editing level has the effect of suspending whatever command invoked it and permitting the user to do arbitrary editing before resuming that command.
The commands available during recursive editing are the same ones available in the top-level editing loop and defined in the keymaps. Only a few special commands exit the recursive editing level; the others return to the recursive editing level when they finish. (The special commands for exiting are always available, but they do nothing when recursive editing is not in progress.)
All command loops, including recursive ones, set up all-purpose error handlers so that an error in a command run from the command loop will not exit the loop.
Minibuffer input is a special kind of recursive editing. It has a few special wrinkles, such as enabling display of the minibuffer and the minibuffer window, but fewer than you might suppose. Certain keys behave differently in the minibuffer, but that is only because of the minibuffer's local map; if you switch windows, you get the usual Emacs commands.
To invoke a recursive editing level, call the function
recursive-edit. This function contains the command loop; it also
contains a call to catch with tag exit, which makes it
possible to exit the recursive editing level by throwing to exit
(see Catch and Throw). If you throw a value other than t,
then recursive-edit returns normally to the function that called
it. The command C-M-c (exit-recursive-edit) does this.
Throwing a t value causes recursive-edit to quit, so that
control returns to the command loop one level up. This is called
aborting, and is done by C-] (abort-recursive-edit).
Most applications should not use recursive editing, except as part of using the minibuffer. Usually it is more convenient for the user if you change the major mode of the current buffer temporarily to a special major mode, which should have a command to go back to the previous mode. (The e command in Rmail uses this technique.) Or, if you wish to give the user different text to edit recursively, create and select a new buffer in a special mode. In this mode, define a command to complete the processing and go back to the previous buffer. (The m command in Rmail does this.)
Recursive edits are useful in debugging. You can insert a call to
debug into a function definition as a sort of breakpoint, so that
you can look around when the function gets there. debug invokes
a recursive edit but also provides the other features of the debugger.
Recursive editing levels are also used when you type C-r in
query-replace or use C-x q (kbd-macro-query).
This function invokes the editor command loop. It is called automatically by the initialization of Emacs, to let the user begin editing. When called from a Lisp program, it enters a recursive editing level.
If the current buffer is not the same as the selected window's buffer,
recursive-editsaves and restores the current buffer. Otherwise, if you switch buffers, the buffer you switched to is current afterrecursive-editreturns.In the following example, the function
simple-recfirst advances point one word, then enters a recursive edit, printing out a message in the echo area. The user can then do any editing desired, and then type C-M-c to exit and continue executingsimple-rec.(defun simple-rec () (forward-word 1) (message "Recursive edit in progress") (recursive-edit) (forward-word 1)) => simple-rec (simple-rec) => nil
This function exits from the innermost recursive edit (including minibuffer input). Its definition is effectively
(throw 'exit nil).
This function aborts the command that requested the innermost recursive edit (including minibuffer input), by signaling
quitafter exiting the recursive edit. Its definition is effectively(throw 'exit t). See Quitting.
This function exits all recursive editing levels; it does not return a value, as it jumps completely out of any computation directly back to the main command loop.
This function returns the current depth of recursive edits. When no recursive edit is active, it returns 0.
Disabling a command marks the command as requiring user confirmation before it can be executed. Disabling is used for commands which might be confusing to beginning users, to prevent them from using the commands by accident.
The low-level mechanism for disabling a command is to put a
non-nil disabled property on the Lisp symbol for the
command. These properties are normally set up by the user's
init file (see Init File) with Lisp expressions such as this:
(put 'upcase-region 'disabled t)
For a few commands, these properties are present by default (you can remove them in your init file if you wish).
If the value of the disabled property is a string, the message
saying the command is disabled includes that string. For example:
(put 'delete-region 'disabled
"Text deleted this way cannot be yanked back!\n")
See Disabling, for the details on what happens when a disabled command is invoked interactively. Disabling a command has no effect on calling it as a function from Lisp programs.
Allow command (a symbol) to be executed without special confirmation from now on, and alter the user's init file (see Init File) so that this will apply to future sessions.
Require special confirmation to execute command from now on, and alter the user's init file so that this will apply to future sessions.
The value of this variable should be a function. When the user invokes a disabled command interactively, this function is called instead of the disabled command. It can use
this-command-keysto determine what the user typed to run the command, and thus find the command itself.The value may also be
nil. Then all commands work normally, even disabled ones.By default, the value is a function that asks the user whether to proceed.
The command loop keeps a history of the complex commands that have
been executed, to make it convenient to repeat these commands. A
complex command is one for which the interactive argument reading
uses the minibuffer. This includes any M-x command, any
M-: command, and any command whose interactive
specification reads an argument from the minibuffer. Explicit use of
the minibuffer during the execution of the command itself does not cause
the command to be considered complex.
This variable's value is a list of recent complex commands, each represented as a form to evaluate. It continues to accumulate all complex commands for the duration of the editing session, but when it reaches the maximum size (see Minibuffer History), the oldest elements are deleted as new ones are added.
command-history => ((switch-to-buffer "chistory.texi") (describe-key "^X^[") (visit-tags-table "~/emacs/src/") (find-tag "repeat-complex-command"))
This history list is actually a special case of minibuffer history (see Minibuffer History), with one special twist: the elements are expressions rather than strings.
There are a number of commands devoted to the editing and recall of
previous commands. The commands repeat-complex-command, and
list-command-history are described in the user manual
(see Repetition). Within the
minibuffer, the usual minibuffer history commands are available.
A keyboard macro is a canned sequence of input events that can be considered a command and made the definition of a key. The Lisp representation of a keyboard macro is a string or vector containing the events. Don't confuse keyboard macros with Lisp macros (see Macros).
This function executes kbdmacro as a sequence of events. If kbdmacro is a string or vector, then the events in it are executed exactly as if they had been input by the user. The sequence is not expected to be a single key sequence; normally a keyboard macro definition consists of several key sequences concatenated.
If kbdmacro is a symbol, then its function definition is used in place of kbdmacro. If that is another symbol, this process repeats. Eventually the result should be a string or vector. If the result is not a symbol, string, or vector, an error is signaled.
The argument count is a repeat count; kbdmacro is executed that many times. If count is omitted or
nil, kbdmacro is executed once. If it is 0, kbdmacro is executed over and over until it encounters an error or a failing search.If loopfunc is non-
nil, it is a function that is called, without arguments, prior to each iteration of the macro. If loopfunc returnsnil, then this stops execution of the macro.See Reading One Event, for an example of using
execute-kbd-macro.
This variable contains the string or vector that defines the keyboard macro that is currently executing. It is
nilif no macro is currently executing. A command can test this variable so as to behave differently when run from an executing macro. Do not set this variable yourself.
This variable is non-
nilif and only if a keyboard macro is being defined. A command can test this variable so as to behave differently while a macro is being defined. The value isappendwhile appending to the definition of an existing macro. The commandsstart-kbd-macro,kmacro-start-macroandend-kbd-macroset this variable—do not set it yourself.The variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
This variable is the definition of the most recently defined keyboard macro. Its value is a string or vector, or
nil.The variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
This normal hook is run when a keyboard macro terminates, regardless of what caused it to terminate (reaching the macro end or an error which ended the macro prematurely).
The command bindings of input events are recorded in data structures called keymaps. Each entry in a keymap associates (or binds) an individual event type, either to another keymap or to a command. When an event type is bound to a keymap, that keymap is used to look up the next input event; this continues until a command is found. The whole process is called key lookup.
A key sequence, or key for short, is a sequence of one
or more input events that form a unit. Input events include
characters, function keys, mouse actions, or system events external to
Emacs, such as iconify-frame (see Input Events).
The Emacs Lisp representation for a key sequence is a string or
vector. Unless otherwise stated, any Emacs Lisp function that accepts
a key sequence as an argument can handle both representations.
In the string representation, alphanumeric characters ordinarily
stand for themselves; for example, "a" represents a
and "2" represents 2. Control character events are
prefixed by the substring "\C-", and meta characters by
"\M-"; for example, "\C-x" represents the key C-x.
In addition, the <TAB>, <RET>, <ESC>, and <DEL> events
are represented by "\t", "\r", "\e", and
"\d" respectively. The string representation of a complete key
sequence is the concatenation of the string representations of the
constituent events; thus, "\C-xl" represents the key sequence
C-x l.
Key sequences containing function keys, mouse button events, system events, or non-ASCII characters such as C-= or H-a cannot be represented as strings; they have to be represented as vectors.
In the vector representation, each element of the vector represents
an input event, in its Lisp form. See Input Events. For example,
the vector [?\C-x ?l] represents the key sequence C-x l.
For examples of key sequences written in string and vector representations, Init Rebinding.
This function converts the text keyseq-text (a string constant) into a key sequence (a string or vector constant). The contents of keyseq-text should use the same syntax as in the buffer invoked by the C-x C-k <RET> (
kmacro-edit-macro) command; in particular, you must surround function key names with `<...>'. See Edit Keyboard Macro.(kbd "C-x") => "\C-x" (kbd "C-x C-f") => "\C-x\C-f" (kbd "C-x 4 C-f") => "\C-x4\C-f" (kbd "X") => "X" (kbd "RET") => "\^M" (kbd "C-c SPC") => "\C-c " (kbd "<f1> SPC") => [f1 32] (kbd "C-M-<down>") => [C-M-down]
A keymap is a Lisp data structure that specifies key bindings for various key sequences.
A single keymap directly specifies definitions for individual events. When a key sequence consists of a single event, its binding in a keymap is the keymap's definition for that event. The binding of a longer key sequence is found by an iterative process: first find the definition of the first event (which must itself be a keymap); then find the second event's definition in that keymap, and so on until all the events in the key sequence have been processed.
If the binding of a key sequence is a keymap, we call the key sequence
a prefix key. Otherwise, we call it a complete key (because
no more events can be added to it). If the binding is nil,
we call the key undefined. Examples of prefix keys are C-c,
C-x, and C-x 4. Examples of defined complete keys are
X, <RET>, and C-x 4 C-f. Examples of undefined complete
keys are C-x C-g, and C-c 3. See Prefix Keys, for more
details.
The rule for finding the binding of a key sequence assumes that the intermediate bindings (found for the events before the last) are all keymaps; if this is not so, the sequence of events does not form a unit—it is not really one key sequence. In other words, removing one or more events from the end of any valid key sequence must always yield a prefix key. For example, C-f C-n is not a key sequence; C-f is not a prefix key, so a longer sequence starting with C-f cannot be a key sequence.
The set of possible multi-event key sequences depends on the bindings for prefix keys; therefore, it can be different for different keymaps, and can change when bindings are changed. However, a one-event sequence is always a key sequence, because it does not depend on any prefix keys for its well-formedness.
At any time, several primary keymaps are active—that is, in use for finding key bindings. These are the global map, which is shared by all buffers; the local keymap, which is usually associated with a specific major mode; and zero or more minor mode keymaps, which belong to currently enabled minor modes. (Not all minor modes have keymaps.) The local keymap bindings shadow (i.e., take precedence over) the corresponding global bindings. The minor mode keymaps shadow both local and global keymaps. See Active Keymaps, for details.
Each keymap is a list whose car is the symbol keymap. The
remaining elements of the list define the key bindings of the keymap.
A symbol whose function definition is a keymap is also a keymap. Use
the function keymapp (see below) to test whether an object is a
keymap.
Several kinds of elements may appear in a keymap, after the symbol
keymap that begins it:
(type . binding)
(type item-name . binding)
(type item-name help-string . binding)
(type menu-item . details)
(t . binding)
nil (see below).
(keymap ...)make-composed-keymap.
When the binding is nil, it doesn't constitute a definition
but it does take precedence over a default binding or a binding in the
parent keymap. On the other hand, a binding of nil does
not override lower-precedence keymaps; thus, if the local map
gives a binding of nil, Emacs uses the binding from the
global map.
Keymaps do not directly record bindings for the meta characters.
Instead, meta characters are regarded for purposes of key lookup as
sequences of two characters, the first of which is <ESC> (or
whatever is currently the value of meta-prefix-char). Thus, the
key M-a is internally represented as <ESC> a, and its
global binding is found at the slot for a in esc-map
(see Prefix Keys).
This conversion applies only to characters, not to function keys or other input events; thus, M-<end> has nothing to do with <ESC> <end>.
Here as an example is the local keymap for Lisp mode, a sparse keymap. It defines bindings for <DEL>, C-c C-z, C-M-q, and C-M-x (the actual value also contains a menu binding, which is omitted here for the sake of brevity).
lisp-mode-map
=>
(keymap
(3 keymap
;; C-c C-z
(26 . run-lisp))
(27 keymap
;; C-M-x, treated as <ESC> C-x
(24 . lisp-send-defun))
;; This part is inherited from lisp-mode-shared-map.
keymap
;; <DEL>
(127 . backward-delete-char-untabify)
(27 keymap
;; C-M-q, treated as <ESC> C-q
(17 . indent-sexp)))
This function returns
tif object is a keymap,nilotherwise. More precisely, this function tests for a list whose car iskeymap, or for a symbol whose function definition satisfieskeymapp.(keymapp '(keymap)) => t (fset 'foo '(keymap)) (keymapp 'foo) => t (keymapp (current-global-map)) => t
Here we describe the functions for creating keymaps.
This function creates and returns a new sparse keymap with no entries. (A sparse keymap is the kind of keymap you usually want.) The new keymap does not contain a char-table, unlike
make-keymap, and does not bind any events.(make-sparse-keymap) => (keymap)If you specify prompt, that becomes the overall prompt string for the keymap. You should specify this only for menu keymaps (see Defining Menus). A keymap with an overall prompt string will always present a mouse menu or a keyboard menu if it is active for looking up the next input event. Don't specify an overall prompt string for the main map of a major or minor mode, because that would cause the command loop to present a keyboard menu every time.
This function creates and returns a new full keymap. That keymap contains a char-table (see Char-Tables) with slots for all characters without modifiers. The new keymap initially binds all these characters to
nil, and does not bind any other kind of event. The argument prompt specifies a prompt string, as inmake-sparse-keymap.(make-keymap) => (keymap #^[nil nil keymap nil nil nil ...])A full keymap is more efficient than a sparse keymap when it holds lots of bindings; for just a few, the sparse keymap is better.
This function returns a copy of keymap. Any keymaps that appear directly as bindings in keymap are also copied recursively, and so on to any number of levels. However, recursive copying does not take place when the definition of a character is a symbol whose function definition is a keymap; the same symbol appears in the new copy.
(setq map (copy-keymap (current-local-map))) => (keymap ;; (This implements meta characters.) (27 keymap (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) (eq map (current-local-map)) => nil (equal map (current-local-map)) => t
A keymap can inherit the bindings of another keymap, which we call the parent keymap. Such a keymap looks like this:
(keymap elements... . parent-keymap)
The effect is that this keymap inherits all the bindings of parent-keymap, whatever they may be at the time a key is looked up, but can add to them or override them with elements.
If you change the bindings in parent-keymap using
define-key or other key-binding functions, these changed
bindings are visible in the inheriting keymap, unless shadowed by the
bindings made by elements. The converse is not true: if you use
define-key to change bindings in the inheriting keymap, these
changes are recorded in elements, but have no effect on
parent-keymap.
The proper way to construct a keymap with a parent is to use
set-keymap-parent; if you have code that directly constructs a
keymap with a parent, please convert the program to use
set-keymap-parent instead.
This returns the parent keymap of keymap. If keymap has no parent,
keymap-parentreturnsnil.
This sets the parent keymap of keymap to parent, and returns parent. If parent is
nil, this function gives keymap no parent at all.If keymap has submaps (bindings for prefix keys), they too receive new parent keymaps that reflect what parent specifies for those prefix keys.
Here is an example showing how to make a keymap that inherits
from text-mode-map:
(let ((map (make-sparse-keymap)))
(set-keymap-parent map text-mode-map)
map)
A non-sparse keymap can have a parent too, but this is not very
useful. A non-sparse keymap always specifies something as the binding
for every numeric character code without modifier bits, even if it is
nil, so these character's bindings are never inherited from
the parent keymap.
Sometimes you want to make a keymap that inherits from more than one
map. You can use the function make-composed-keymap for this.
This function returns a new keymap composed of the existing keymap(s) maps, and optionally inheriting from a parent keymap parent. maps can be a single keymap or a list of more than one. When looking up a key in the resulting new map, Emacs searches in each of the maps in turn, and then in parent, stopping at the first match. A
nilbinding in any one of maps overrides any binding in parent, but it does not override any non-nilbinding in any other of the maps.
For example, here is how Emacs sets the parent of
help-mode-map, such that it inherits from both
button-buffer-map and special-mode-map:
(defvar help-mode-map
(let ((map (make-sparse-keymap)))
(set-keymap-parent map
(make-composed-keymap button-buffer-map special-mode-map))
... map) ... )
A prefix key is a key sequence whose binding is a keymap. The
keymap defines what to do with key sequences that extend the prefix key.
For example, C-x is a prefix key, and it uses a keymap that is
also stored in the variable ctl-x-map. This keymap defines
bindings for key sequences starting with C-x.
Some of the standard Emacs prefix keys use keymaps that are also found in Lisp variables:
esc-map is the global keymap for the <ESC> prefix key. Thus,
the global definitions of all meta characters are actually found here.
This map is also the function definition of ESC-prefix.
help-map is the global keymap for the C-h prefix key.
mode-specific-map is the global keymap for the prefix key
C-c. This map is actually global, not mode-specific, but its name
provides useful information about C-c in the output of C-h b
(display-bindings), since the main use of this prefix key is for
mode-specific bindings.
ctl-x-map is the global keymap used for the C-x prefix key.
This map is found via the function cell of the symbol
Control-X-prefix.
mule-keymap is the global keymap used for the C-x <RET>
prefix key.
ctl-x-4-map is the global keymap used for the C-x 4 prefix
key.
ctl-x-5-map is the global keymap used for the C-x 5 prefix
key.
2C-mode-map is the global keymap used for the C-x 6 prefix
key.
vc-prefix-map is the global keymap used for the C-x v prefix
key.
goto-map is the global keymap used for the M-g prefix
key.
search-map is the global keymap used for the M-s prefix
key.
facemenu-keymap is the global keymap used for the M-o
prefix key.
The keymap binding of a prefix key is used for looking up the event
that follows the prefix key. (It may instead be a symbol whose function
definition is a keymap. The effect is the same, but the symbol serves
as a name for the prefix key.) Thus, the binding of C-x is the
symbol Control-X-prefix, whose function cell holds the keymap
for C-x commands. (The same keymap is also the value of
ctl-x-map.)
Prefix key definitions can appear in any active keymap. The definitions of C-c, C-x, C-h and <ESC> as prefix keys appear in the global map, so these prefix keys are always available. Major and minor modes can redefine a key as a prefix by putting a prefix key definition for it in the local map or the minor mode's map. See Active Keymaps.
If a key is defined as a prefix in more than one active map, then its various definitions are in effect merged: the commands defined in the minor mode keymaps come first, followed by those in the local map's prefix definition, and then by those from the global map.
In the following example, we make C-p a prefix key in the local
keymap, in such a way that C-p is identical to C-x. Then
the binding for C-p C-f is the function find-file, just
like C-x C-f. The key sequence C-p 6 is not found in any
active keymap.
(use-local-map (make-sparse-keymap))
=> nil
(local-set-key "\C-p" ctl-x-map)
=> nil
(key-binding "\C-p\C-f")
=> find-file
(key-binding "\C-p6")
=> nil
This function prepares symbol for use as a prefix key's binding: it creates a sparse keymap and stores it as symbol's function definition. Subsequently binding a key sequence to symbol will make that key sequence into a prefix key. The return value is
symbol.This function also sets symbol as a variable, with the keymap as its value. But if mapvar is non-
nil, it sets mapvar as a variable instead.If prompt is non-
nil, that becomes the overall prompt string for the keymap. The prompt string should be given for menu keymaps (see Defining Menus).
Emacs contains many keymaps, but at any time only a few keymaps are active. When Emacs receives user input, it translates the input event (see Translation Keymaps), and looks for a key binding in the active keymaps.
Usually, the active keymaps are: (i) the keymap specified by the
keymap property, (ii) the keymaps of enabled minor modes, (iii)
the current buffer's local keymap, and (iv) the global keymap, in that
order. Emacs searches for each input key sequence in all these
keymaps.
Of these usual keymaps, the highest-precedence one is specified
by the keymap text or overlay property at point, if any. (For
a mouse input event, Emacs uses the event position instead of point;
see Searching Keymaps.)
Next in precedence are keymaps specified by enabled minor modes.
These keymaps, if any, are specified by the variables
emulation-mode-map-alists,
minor-mode-overriding-map-alist, and
minor-mode-map-alist. See Controlling Active Maps.
Next in precedence is the buffer's local keymap, containing
key bindings specific to the buffer. The minibuffer also has a local
keymap (see Intro to Minibuffers). If there is a local-map
text or overlay property at point, that specifies the local keymap to
use, in place of the buffer's default local keymap.
The local keymap is normally set by the buffer's major mode, and
every buffer with the same major mode shares the same local keymap.
Hence, if you call local-set-key (see Key Binding Commands)
to change the local keymap in one buffer, that also affects the local
keymaps in other buffers with the same major mode.
Finally, the global keymap contains key bindings that are
defined regardless of the current buffer, such as C-f. It is
always active, and is bound to the variable global-map.
Apart from the above usual keymaps, Emacs provides special ways
for programs to make other keymaps active. Firstly, the variable
overriding-local-map specifies a keymap that replaces the usual
active keymaps, except for the global keymap. Secondly, the
terminal-local variable overriding-terminal-local-map specifies
a keymap that takes precedence over all other keymaps
(including overriding-local-map); this is normally used for
modal/transient keybindings (the function set-transient-map
provides a convenient interface for this). See Controlling Active Maps, for details.
Making keymaps active is not the only way to use them. Keymaps are
also used in other ways, such as for translating events within
read-key-sequence. See Translation Keymaps.
See Standard Keymaps, for a list of some standard keymaps.
This returns the list of active keymaps that would be used by the command loop in the current circumstances to look up a key sequence. Normally it ignores
overriding-local-mapandoverriding-terminal-local-map, but if olp is non-nilthen it pays attention to them. position can optionally be either an event position as returned byevent-startor a buffer position, and may change the keymaps as described forkey-binding.
This function returns the binding for key according to the current active keymaps. The result is
nilif key is undefined in the keymaps.The argument accept-defaults controls checking for default bindings, as in
lookup-key(see Functions for Key Lookup).When commands are remapped (see Remapping Commands),
key-bindingnormally processes command remappings so as to return the remapped command that will actually be executed. However, if no-remap is non-nil,key-bindingignores remappings and returns the binding directly specified for key.If key starts with a mouse event (perhaps following a prefix event), the maps to be consulted are determined based on the event's position. Otherwise, they are determined based on the value of point. However, you can override either of them by specifying position. If position is non-
nil, it should be either a buffer position or an event position like the value ofevent-start. Then the maps consulted are determined based on position.Emacs signals an error if key is not a string or a vector.
(key-binding "\C-x\C-f") => find-file
Here is a pseudo-Lisp summary of how Emacs searches the active keymaps:
(or (if overriding-terminal-local-map
(find-in overriding-terminal-local-map))
(if overriding-local-map
(find-in overriding-local-map)
(or (find-in (get-char-property (point) 'keymap))
(find-in-any emulation-mode-map-alists)
(find-in-any minor-mode-overriding-map-alist)
(find-in-any minor-mode-map-alist)
(if (get-text-property (point) 'local-map)
(find-in (get-char-property (point) 'local-map))
(find-in (current-local-map)))))
(find-in (current-global-map)))
Here, find-in and find-in-any are pseudo functions that
search in one keymap and in an alist of keymaps, respectively. Note
that the set-transient-map function works by setting
overriding-terminal-local-map (see Controlling Active Maps).
In the above pseudo-code, if a key sequence starts with a mouse
event (see Mouse Events), that event's position is used instead of
point, and the event's buffer is used instead of the current buffer.
In particular, this affects how the keymap and local-map
properties are looked up. If a mouse event occurs on a string
embedded with a display, before-string, or
after-string property (see Special Properties), and the
string has a non-nil keymap or local-map
property, that overrides the corresponding property in the underlying
buffer text (i.e., the property specified by the underlying text is
ignored).
When a key binding is found in one of the active keymaps, and that binding is a command, the search is over—the command is executed. However, if the binding is a symbol with a value or a string, Emacs replaces the input key sequences with the variable's value or the string, and restarts the search of the active keymaps. See Key Lookup.
The command which is finally found might also be remapped. See Remapping Commands.
This variable contains the default global keymap that maps Emacs keyboard input to commands. The global keymap is normally this keymap. The default global keymap is a full keymap that binds
self-insert-commandto all of the printing characters.It is normal practice to change the bindings in the global keymap, but you should not assign this variable any value other than the keymap it starts out with.
This function returns the current global keymap. This is the same as the value of
global-mapunless you change one or the other. The return value is a reference, not a copy; if you usedefine-keyor other functions on it you will alter global bindings.(current-global-map) => (keymap [set-mark-command beginning-of-line ... delete-backward-char])
This function returns the current buffer's local keymap, or
nilif it has none. In the following example, the keymap for the *scratch* buffer (using Lisp Interaction mode) is a sparse keymap in which the entry for <ESC>, ASCII code 27, is another sparse keymap.(current-local-map) => (keymap (10 . eval-print-last-sexp) (9 . lisp-indent-line) (127 . backward-delete-char-untabify) (27 keymap (24 . eval-defun) (17 . indent-sexp)))
current-local-map returns a reference to the local keymap, not
a copy of it; if you use define-key or other functions on it
you will alter local bindings.
This function returns a list of the keymaps of currently enabled minor modes.
This function makes keymap the new current global keymap. It returns
nil.It is very unusual to change the global keymap.
This function makes keymap the new local keymap of the current buffer. If keymap is
nil, then the buffer has no local keymap.use-local-mapreturnsnil. Most major mode commands use this function.
This variable is an alist describing keymaps that may or may not be active according to the values of certain variables. Its elements look like this:
(variable . keymap)The keymap keymap is active whenever variable has a non-
nilvalue. Typically variable is the variable that enables or disables a minor mode. See Keymaps and Minor Modes.Note that elements of
minor-mode-map-alistdo not have the same structure as elements ofminor-mode-alist. The map must be the cdr of the element; a list with the map as the second element will not do. The cdr can be either a keymap (a list) or a symbol whose function definition is a keymap.When more than one minor mode keymap is active, the earlier one in
minor-mode-map-alisttakes priority. But you should design minor modes so that they don't interfere with each other. If you do this properly, the order will not matter.See Keymaps and Minor Modes, for more information about minor modes. See also
minor-mode-key-binding(see Functions for Key Lookup).
This variable allows major modes to override the key bindings for particular minor modes. The elements of this alist look like the elements of
minor-mode-map-alist:(variable.keymap).If a variable appears as an element of
minor-mode-overriding-map-alist, the map specified by that element totally replaces any map specified for the same variable inminor-mode-map-alist.
minor-mode-overriding-map-alistis automatically buffer-local in all buffers.
If non-
nil, this variable holds a keymap to use instead of the buffer's local keymap, any text property or overlay keymaps, and any minor mode keymaps. This keymap, if specified, overrides all other maps that would have been active, except for the current global map.
If non-
nil, this variable holds a keymap to use instead ofoverriding-local-map, the buffer's local keymap, text property or overlay keymaps, and all the minor mode keymaps.This variable is always local to the current terminal and cannot be buffer-local. See Multiple Terminals. It is used to implement incremental search mode.
If this variable is non-
nil, the value ofoverriding-local-maporoverriding-terminal-local-mapcan affect the display of the menu bar. The default value isnil, so those map variables have no effect on the menu bar.Note that these two map variables do affect the execution of key sequences entered using the menu bar, even if they do not affect the menu bar display. So if a menu bar key sequence comes in, you should clear the variables before looking up and executing that key sequence. Modes that use the variables would typically do this anyway; normally they respond to events that they do not handle by “unreading” them and exiting.
This variable holds a keymap for special events. If an event type has a binding in this keymap, then it is special, and the binding for the event is run directly by
read-event. See Special Events.
This variable holds a list of keymap alists to use for emulation modes. It is intended for modes or packages using multiple minor-mode keymaps. Each element is a keymap alist which has the same format and meaning as
minor-mode-map-alist, or a symbol with a variable binding which is such an alist. The active keymaps in each alist are used beforeminor-mode-map-alistandminor-mode-overriding-map-alist.
This function adds keymap as a transient keymap, which takes precedence over other keymaps for one (or more) subsequent keys.
Normally, keymap is used just once, to look up the very next key. If the optional argument keep-pred is
t, the map stays active as long as the user types keys defined in keymap; when the user types a key that is not in keymap, the transient keymap is deactivated and normal key lookup continues for that key.The keep-pred argument can also be a function. In that case, the function is called with no arguments, prior to running each command, while keymap is active; it should return non-
nilif keymap should stay active.The optional argument on-exit, if non-nil, specifies a function that is called, with no arguments, after keymap is deactivated.
This function works by adding and removing keymap from the variable
overriding-terminal-local-map, which takes precedence over all other active keymaps (see Searching Keymaps).
Key lookup is the process of finding the binding of a key sequence from a given keymap. The execution or use of the binding is not part of key lookup.
Key lookup uses just the event type of each event in the key sequence;
the rest of the event is ignored. In fact, a key sequence used for key
lookup may designate a mouse event with just its types (a symbol)
instead of the entire event (a list). See Input Events. Such
a key sequence is insufficient for command-execute to run,
but it is sufficient for looking up or rebinding a key.
When the key sequence consists of multiple events, key lookup processes the events sequentially: the binding of the first event is found, and must be a keymap; then the second event's binding is found in that keymap, and so on until all the events in the key sequence are used up. (The binding thus found for the last event may or may not be a keymap.) Thus, the process of key lookup is defined in terms of a simpler process for looking up a single event in a keymap. How that is done depends on the type of object associated with the event in that keymap.
Let's use the term keymap entry to describe the value found by
looking up an event type in a keymap. (This doesn't include the item
string and other extra elements in a keymap element for a menu item, because
lookup-key and other key lookup functions don't include them in
the returned value.) While any Lisp object may be stored in a keymap
as a keymap entry, not all make sense for key lookup. Here is a table
of the meaningful types of keymap entries:
nilnil means that the events used so far in the lookup form an
undefined key. When a keymap fails to mention an event type at all, and
has no default binding, that is equivalent to a binding of nil
for that event type.
keymap, then the list
is a keymap, and is treated as a keymap (see above).
lambda, then the list is a
lambda expression. This is presumed to be a function, and is treated
as such (see above). In order to execute properly as a key binding,
this function must be a command—it must have an interactive
specification. See Defining Commands.
Note that keymaps and keyboard macros (strings and vectors) are not
valid functions, so a symbol with a keymap, string, or vector as its
function definition is invalid as a function. It is, however, valid as
a key binding. If the definition is a keyboard macro, then the symbol
is also valid as an argument to command-execute
(see Interactive Call).
The symbol undefined is worth special mention: it means to treat
the key as undefined. Strictly speaking, the key is defined, and its
binding is the command undefined; but that command does the same
thing that is done automatically for an undefined key: it rings the bell
(by calling ding) but does not signal an error.
undefined is used in local keymaps to override a global key
binding and make the key undefined locally. A local binding of
nil would fail to do this because it would not override the
global binding.
In short, a keymap entry may be a keymap, a command, a keyboard
macro, a symbol that leads to one of them, or nil.
Here are the functions and variables pertaining to key lookup.
This function returns the definition of key in keymap. All the other functions described in this chapter that look up keys use
lookup-key. Here are examples:(lookup-key (current-global-map) "\C-x\C-f") => find-file (lookup-key (current-global-map) (kbd "C-x C-f")) => find-file (lookup-key (current-global-map) "\C-x\C-f12345") => 2If the string or vector key is not a valid key sequence according to the prefix keys specified in keymap, it must be too long and have extra events at the end that do not fit into a single key sequence. Then the value is a number, the number of events at the front of key that compose a complete key.
If accept-defaults is non-
nil, thenlookup-keyconsiders default bindings as well as bindings for the specific events in key. Otherwise,lookup-keyreports only bindings for the specific sequence key, ignoring default bindings except when you explicitly ask about them. (To do this, supplytas an element of key; see Format of Keymaps.)If key contains a meta character (not a function key), that character is implicitly replaced by a two-character sequence: the value of
meta-prefix-char, followed by the corresponding non-meta character. Thus, the first example below is handled by conversion into the second example.(lookup-key (current-global-map) "\M-f") => forward-word (lookup-key (current-global-map) "\ef") => forward-wordUnlike
read-key-sequence, this function does not modify the specified events in ways that discard information (see Key Sequence Input). In particular, it does not convert letters to lower case and it does not change drag events to clicks.
This function returns the binding for key in the current local keymap, or
nilif it is undefined there.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This function returns the binding for command key in the current global keymap, or
nilif it is undefined there.The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This function returns a list of all the active minor mode bindings of key. More precisely, it returns an alist of pairs
(modename.binding), where modename is the variable that enables the minor mode, and binding is key's binding in that mode. If key has no minor-mode bindings, the value isnil.If the first binding found is not a prefix definition (a keymap or a symbol defined as a keymap), all subsequent bindings from other minor modes are omitted, since they would be completely shadowed. Similarly, the list omits non-prefix bindings that follow prefix bindings.
The argument accept-defaults controls checking for default bindings, as in
lookup-key(above).
This variable is the meta-prefix character code. It is used for translating a meta character to a two-character sequence so it can be looked up in a keymap. For useful results, the value should be a prefix event (see Prefix Keys). The default value is 27, which is the ASCII code for <ESC>.
As long as the value of
meta-prefix-charremains 27, key lookup translates M-b into <ESC> b, which is normally defined as thebackward-wordcommand. However, if you were to setmeta-prefix-charto 24, the code for C-x, then Emacs will translate M-b into C-x b, whose standard binding is theswitch-to-buffercommand. (Don't actually do this!) Here is an illustration of what would happen:meta-prefix-char ; The default value. => 27 (key-binding "\M-b") => backward-word ?\C-x ; The print representation => 24 ; of a character. (setq meta-prefix-char 24) => 24 (key-binding "\M-b") => switch-to-buffer ; Now, typing M-b is ; like typing C-x b. (setq meta-prefix-char 27) ; Avoid confusion! => 27 ; Restore the default value!This translation of one event into two happens only for characters, not for other kinds of input events. Thus, M-<F1>, a function key, is not converted into <ESC> <F1>.
The way to rebind a key is to change its entry in a keymap. If you
change a binding in the global keymap, the change is effective in all
buffers (though it has no direct effect in buffers that shadow the
global binding with a local one). If you change the current buffer's
local map, that usually affects all buffers using the same major mode.
The global-set-key and local-set-key functions are
convenient interfaces for these operations (see Key Binding Commands). You can also use define-key, a more general
function; then you must explicitly specify the map to change.
When choosing the key sequences for Lisp programs to rebind, please follow the Emacs conventions for use of various keys (see Key Binding Conventions).
In writing the key sequence to rebind, it is good to use the special
escape sequences for control and meta characters (see String Type).
The syntax `\C-' means that the following character is a control
character and `\M-' means that the following character is a meta
character. Thus, the string "\M-x" is read as containing a
single M-x, "\C-f" is read as containing a single
C-f, and "\M-\C-x" and "\C-\M-x" are both read as
containing a single C-M-x. You can also use this escape syntax in
vectors, as well as others that aren't allowed in strings; one example
is `[?\C-\H-x home]'. See Character Type.
The key definition and lookup functions accept an alternate syntax for
event types in a key sequence that is a vector: you can use a list
containing modifier names plus one base event (a character or function
key name). For example, (control ?a) is equivalent to
?\C-a and (hyper control left) is equivalent to
C-H-left. One advantage of such lists is that the precise
numeric codes for the modifier bits don't appear in compiled files.
The functions below signal an error if keymap is not a keymap,
or if key is not a string or vector representing a key sequence.
You can use event types (symbols) as shorthand for events that are
lists. The kbd function (see Key Sequences) is a
convenient way to specify the key sequence.
This function sets the binding for key in keymap. (If key is more than one event long, the change is actually made in another keymap reached from keymap.) The argument binding can be any Lisp object, but only certain types are meaningful. (For a list of meaningful types, see Key Lookup.) The value returned by
define-keyis binding.If key is
[t], this sets the default binding in keymap. When an event has no binding of its own, the Emacs command loop uses the keymap's default binding, if there is one.Every prefix of key must be a prefix key (i.e., bound to a keymap) or undefined; otherwise an error is signaled. If some prefix of key is undefined, then
define-keydefines it as a prefix key so that the rest of key can be defined as specified.If there was previously no binding for key in keymap, the new binding is added at the beginning of keymap. The order of bindings in a keymap makes no difference for keyboard input, but it does matter for menu keymaps (see Menu Keymaps).
This example creates a sparse keymap and makes a number of bindings in it:
(setq map (make-sparse-keymap))
=> (keymap)
(define-key map "\C-f" 'forward-char)
=> forward-char
map
=> (keymap (6 . forward-char))
;; Build sparse submap for C-x and bind f in that.
(define-key map (kbd "C-x f") 'forward-word)
=> forward-word
map
=> (keymap
(24 keymap ; C-x
(102 . forward-word)) ; f
(6 . forward-char)) ; C-f
;; Bind C-p to the ctl-x-map.
(define-key map (kbd "C-p") ctl-x-map)
;; ctl-x-map
=> [nil ... find-file ... backward-kill-sentence]
;; Bind C-f to foo in the ctl-x-map.
(define-key map (kbd "C-p C-f") 'foo)
=> 'foo
map
=> (keymap ; Note foo in ctl-x-map.
(16 keymap [nil ... foo ... backward-kill-sentence])
(24 keymap
(102 . forward-word))
(6 . forward-char))
Note that storing a new binding for C-p C-f actually works by
changing an entry in ctl-x-map, and this has the effect of
changing the bindings of both C-p C-f and C-x C-f in the
default global map.
The function substitute-key-definition scans a keymap for
keys that have a certain binding and rebinds them with a different
binding. Another feature which is cleaner and can often produce the
same results to remap one command into another (see Remapping Commands).
This function replaces olddef with newdef for any keys in keymap that were bound to olddef. In other words, olddef is replaced with newdef wherever it appears. The function returns
nil.For example, this redefines C-x C-f, if you do it in an Emacs with standard bindings:
(substitute-key-definition 'find-file 'find-file-read-only (current-global-map))If oldmap is non-
nil, that changes the behavior ofsubstitute-key-definition: the bindings in oldmap determine which keys to rebind. The rebindings still happen in keymap, not in oldmap. Thus, you can change one map under the control of the bindings in another. For example,(substitute-key-definition 'delete-backward-char 'my-funny-delete my-map global-map)puts the special deletion command in
my-mapfor whichever keys are globally bound to the standard deletion command.Here is an example showing a keymap before and after substitution:
(setq map '(keymap (?1 . olddef-1) (?2 . olddef-2) (?3 . olddef-1))) => (keymap (49 . olddef-1) (50 . olddef-2) (51 . olddef-1)) (substitute-key-definition 'olddef-1 'newdef map) => nil map => (keymap (49 . newdef) (50 . olddef-2) (51 . newdef))
This function changes the contents of the full keymap keymap by remapping
self-insert-commandto the commandundefined(see Remapping Commands). This has the effect of undefining all printing characters, thus making ordinary insertion of text impossible.suppress-keymapreturnsnil.If nodigits is
nil, thensuppress-keymapdefines digits to rundigit-argument, and - to runnegative-argument. Otherwise it makes them undefined like the rest of the printing characters.The
suppress-keymapfunction does not make it impossible to modify a buffer, as it does not suppress commands such asyankandquoted-insert. To prevent any modification of a buffer, make it read-only (see Read Only Buffers).Since this function modifies keymap, you would normally use it on a newly created keymap. Operating on an existing keymap that is used for some other purpose is likely to cause trouble; for example, suppressing
global-mapwould make it impossible to use most of Emacs.This function can be used to initialize the local keymap of a major mode for which insertion of text is not desirable. But usually such a mode should be derived from
special-mode(see Basic Major Modes); then its keymap will automatically inherit fromspecial-mode-map, which is already suppressed. Here is howspecial-mode-mapis defined:(defvar special-mode-map (let ((map (make-sparse-keymap))) (suppress-keymap map) (define-key map "q" 'quit-window) ... map))
A special kind of key binding can be used to remap one command
to another, without having to refer to the key sequence(s) bound to
the original command. To use this feature, make a key binding for a
key sequence that starts with the dummy event remap, followed
by the command name you want to remap; for the binding, specify the
new definition (usually a command name, but possibly any other valid
definition for a key binding).
For example, suppose My mode provides a special command
my-kill-line, which should be invoked instead of
kill-line. To establish this, its mode keymap should contain
the following remapping:
(define-key my-mode-map [remap kill-line] 'my-kill-line)
Then, whenever my-mode-map is active, if the user types
C-k (the default global key sequence for kill-line) Emacs
will instead run my-kill-line.
Note that remapping only takes place through active keymaps; for
example, putting a remapping in a prefix keymap like ctl-x-map
typically has no effect, as such keymaps are not themselves active.
In addition, remapping only works through a single level; in the
following example,
(define-key my-mode-map [remap kill-line] 'my-kill-line)
(define-key my-mode-map [remap my-kill-line] 'my-other-kill-line)
kill-line is not remapped to my-other-kill-line.
Instead, if an ordinary key binding specifies kill-line, it is
remapped to my-kill-line; if an ordinary binding specifies
my-kill-line, it is remapped to my-other-kill-line.
To undo the remapping of a command, remap it to nil; e.g.,
(define-key my-mode-map [remap kill-line] nil)
This function returns the remapping for command (a symbol), given the current active keymaps. If command is not remapped (which is the usual situation), or not a symbol, the function returns
nil.positioncan optionally specify a buffer position or an event position to determine the keymaps to use, as inkey-binding.If the optional argument
keymapsis non-nil, it specifies a list of keymaps to search in. This argument is ignored ifpositionis non-nil.
When the read-key-sequence function reads a key sequence
(see Key Sequence Input), it uses translation keymaps to
translate certain event sequences into others. The translation
keymaps are input-decode-map, local-function-key-map,
and key-translation-map (in order of priority).
Translation keymaps have the same structure as other keymaps, but are used differently: they specify translations to make while reading key sequences, rather than bindings for complete key sequences. As each key sequence is read, it is checked against each translation keymap. If one of the translation keymaps binds k to a vector v, then whenever k appears as a sub-sequence anywhere in a key sequence, that sub-sequence is replaced with the events in v.
For example, VT100 terminals send <ESC> O P when the
keypad key <PF1> is pressed. On such terminals, Emacs must
translate that sequence of events into a single event pf1.
This is done by binding <ESC> O P to [pf1] in
input-decode-map. Thus, when you type C-c <PF1> on
the terminal, the terminal emits the character sequence C-c
<ESC> O P, and read-key-sequence translates this back into
C-c <PF1> and returns it as the vector [?\C-c pf1].
Translation keymaps take effect only after Emacs has decoded the
keyboard input (via the input coding system specified by
keyboard-coding-system). See Terminal I/O Encoding.
This variable holds a keymap that describes the character sequences sent by function keys on an ordinary character terminal.
The value of
input-decode-mapis usually set up automatically according to the terminal's Terminfo or Termcap entry, but sometimes those need help from terminal-specific Lisp files. Emacs comes with terminal-specific files for many common terminals; their main purpose is to make entries ininput-decode-mapbeyond those that can be deduced from Termcap and Terminfo. See Terminal-Specific.
This variable holds a keymap similar to
input-decode-mapexcept that it describes key sequences which should be translated to alternative interpretations that are usually preferred. It applies afterinput-decode-mapand beforekey-translation-map.Entries in
local-function-key-mapare ignored if they conflict with bindings made in the minor mode, local, or global keymaps. I.e., the remapping only applies if the original key sequence would otherwise not have any binding.
local-function-key-mapinherits fromfunction-key-map, but the latter should not be used directly.
This variable is another keymap used just like
input-decode-mapto translate input events into other events. It differs frominput-decode-mapin that it goes to work afterlocal-function-key-mapis finished rather than before; it receives the results of translation bylocal-function-key-map.Just like
input-decode-map, but unlikelocal-function-key-map, this keymap is applied regardless of whether the input key-sequence has a normal binding. Note however that actual key bindings can have an effect onkey-translation-map, even though they are overridden by it. Indeed, actual key bindings overridelocal-function-key-mapand thus may alter the key sequence thatkey-translation-mapreceives. Clearly, it is better to avoid this type of situation.The intent of
key-translation-mapis for users to map one character set to another, including ordinary characters normally bound toself-insert-command.
You can use input-decode-map, local-function-key-map,
and key-translation-map for more than simple aliases, by using
a function, instead of a key sequence, as the translation of a
key. Then this function is called to compute the translation of that
key.
The key translation function receives one argument, which is the prompt
that was specified in read-key-sequence—or nil if the
key sequence is being read by the editor command loop. In most cases
you can ignore the prompt value.
If the function reads input itself, it can have the effect of altering the event that follows. For example, here's how to define C-c h to turn the character that follows into a Hyper character:
(defun hyperify (prompt)
(let ((e (read-event)))
(vector (if (numberp e)
(logior (lsh 1 24) e)
(if (memq 'hyper (event-modifiers e))
e
(add-event-modifier "H-" e))))))
(defun add-event-modifier (string e)
(let ((symbol (if (symbolp e) e (car e))))
(setq symbol (intern (concat string
(symbol-name symbol))))
(if (symbolp e)
symbol
(cons symbol (cdr e)))))
(define-key local-function-key-map "\C-ch" 'hyperify)
The end of a key sequence is detected when that key sequence either is bound to a command, or when Emacs determines that no additional event can lead to a sequence that is bound to a command.
This means that, while input-decode-map and key-translation-map
apply regardless of whether the original key sequence would have a binding, the
presence of such a binding can still prevent translation from taking place.
For example, let us return to our VT100 example above and add a binding for
C-c <ESC> to the global map; now when the user hits C-c
<PF1> Emacs will fail to decode C-c <ESC> O P into C-c
<PF1> because it will stop reading keys right after C-x <ESC>,
leaving O P for later. This is in case the user really hit C-c
<ESC>, in which case Emacs should not sit there waiting for the next key
to decide whether the user really pressed <ESC> or <PF1>.
For that reason, it is better to avoid binding commands to key sequences where the end of the key sequence is a prefix of a key translation. The main such problematic suffixes/prefixes are <ESC>, M-O (which is really <ESC> O) and M-[ (which is really <ESC> [).
This section describes some convenient interactive interfaces for
changing key bindings. They work by calling define-key.
People often use global-set-key in their init files
(see Init File) for simple customization. For example,
(global-set-key (kbd "C-x C-\\") 'next-line)
or
(global-set-key [?\C-x ?\C-\\] 'next-line)
or
(global-set-key [(control ?x) (control ?\\)] 'next-line)
redefines C-x C-\ to move down a line.
(global-set-key [M-mouse-1] 'mouse-set-point)
redefines the first (leftmost) mouse button, entered with the Meta key, to set point where you click.
Be careful when using non-ASCII text characters in Lisp specifications of keys to bind. If these are read as multibyte text, as they usually will be in a Lisp file (see Loading Non-ASCII), you must type the keys as multibyte too. For instance, if you use this:
(global-set-key "ö" 'my-function) ; bind o-umlaut
or
(global-set-key ?ö 'my-function) ; bind o-umlaut
and your language environment is multibyte Latin-1, these commands actually bind the multibyte character with code 246, not the byte code 246 (M-v) sent by a Latin-1 terminal. In order to use this binding, you need to teach Emacs how to decode the keyboard by using an appropriate input method (see Input Methods).
This function sets the binding of key in the current global map to binding.
(global-set-key key binding) == (define-key (current-global-map) key binding)
This function removes the binding of key from the current global map.
One use of this function is in preparation for defining a longer key that uses key as a prefix—which would not be allowed if key has a non-prefix binding. For example:
(global-unset-key "\C-l") => nil (global-set-key "\C-l\C-l" 'redraw-display) => nilThis function is equivalent to using
define-keyas follows:(global-unset-key key) == (define-key (current-global-map) key nil)
This function sets the binding of key in the current local keymap to binding.
(local-set-key key binding) == (define-key (current-local-map) key binding)
This function removes the binding of key from the current local map.
(local-unset-key key) == (define-key (current-local-map) key nil)
This section describes functions used to scan all the current keymaps for the sake of printing help information.
This function returns a list of all the keymaps that can be reached (via zero or more prefix keys) from keymap. The value is an association list with elements of the form
(key.map), where key is a prefix key whose definition in keymap is map.The elements of the alist are ordered so that the key increases in length. The first element is always
([] .keymap), because the specified keymap is accessible from itself with a prefix of no events.If prefix is given, it should be a prefix key sequence; then
accessible-keymapsincludes only the submaps whose prefixes start with prefix. These elements look just as they do in the value of(accessible-keymaps); the only difference is that some elements are omitted.In the example below, the returned alist indicates that the key <ESC>, which is displayed as `^[', is a prefix key whose definition is the sparse keymap
(keymap (83 . center-paragraph) (115 . foo)).(accessible-keymaps (current-local-map)) =>(([] keymap (27 keymap ; Note this keymap for <ESC> is repeated below. (83 . center-paragraph) (115 . center-line)) (9 . tab-to-tab-stop)) ("^[" keymap (83 . center-paragraph) (115 . foo)))In the following example, C-h is a prefix key that uses a sparse keymap starting with
(keymap (118 . describe-variable)...). Another prefix, C-x 4, uses a keymap which is also the value of the variablectl-x-4-map. The eventmode-lineis one of several dummy events used as prefixes for mouse actions in special parts of a window.(accessible-keymaps (current-global-map)) => (([] keymap [set-mark-command beginning-of-line ... delete-backward-char]) ("^H" keymap (118 . describe-variable) ... (8 . help-for-help)) ("^X" keymap [x-flush-mouse-queue ... backward-kill-sentence]) ("^[" keymap [mark-sexp backward-sexp ... backward-kill-word]) ("^X4" keymap (15 . display-buffer) ...) ([mode-line] keymap (S-mouse-2 . mouse-split-window-horizontally) ...))These are not all the keymaps you would see in actuality.
The function
map-keymapcalls function once for each binding in keymap. It passes two arguments, the event type and the value of the binding. If keymap has a parent, the parent's bindings are included as well. This works recursively: if the parent has itself a parent, then the grandparent's bindings are also included and so on.This function is the cleanest way to examine all the bindings in a keymap.
This function is a subroutine used by the
where-iscommand (see Help). It returns a list of all key sequences (of any length) that are bound to command in a set of keymaps.The argument command can be any object; it is compared with all keymap entries using
eq.If keymap is
nil, then the maps used are the current active keymaps, disregardingoverriding-local-map(that is, pretending its value isnil). If keymap is a keymap, then the maps searched are keymap and the global keymap. If keymap is a list of keymaps, only those keymaps are searched.Usually it's best to use
overriding-local-mapas the expression for keymap. Thenwhere-is-internalsearches precisely the keymaps that are active. To search only the global map, pass the value(keymap)(an empty keymap) as keymap.If firstonly is
non-ascii, then the value is a single vector representing the first key sequence found, rather than a list of all possible key sequences. If firstonly ist, then the value is the first key sequence, except that key sequences consisting entirely of ASCII characters (or meta variants of ASCII characters) are preferred to all other key sequences and that the return value can never be a menu binding.If noindirect is non-
nil,where-is-internaldoesn't look inside menu-items to find their commands. This makes it possible to search for a menu-item itself.The fifth argument, no-remap, determines how this function treats command remappings (see Remapping Commands). There are two cases of interest:
- If a command other-command is remapped to command:
- If no-remap is
nil, find the bindings for other-command and treat them as though they are also bindings for command. If no-remap is non-nil, include the vector[remapother-command]in the list of possible key sequences, instead of finding those bindings.
- If command is remapped to other-command:
- If no-remap is
nil, return the bindings for other-command rather than command. If no-remap is non-nil, return the bindings for command, ignoring the fact that it is remapped.
This function creates a listing of all current key bindings, and displays it in a buffer named *Help*. The text is grouped by modes—minor modes first, then the major mode, then global bindings.
If prefix is non-
nil, it should be a prefix key; then the listing includes only keys that start with prefix.When several characters with consecutive ASCII codes have the same definition, they are shown together, as `firstchar..lastchar'. In this instance, you need to know the ASCII codes to understand which characters this means. For example, in the default global map, the characters `<SPC> .. ~' are described by a single line. <SPC> is ASCII 32, ~ is ASCII 126, and the characters between them include all the normal printing characters, (e.g., letters, digits, punctuation, etc.); all these characters are bound to
self-insert-command.If buffer-or-name is non-
nil, it should be a buffer or a buffer name. Thendescribe-bindingslists that buffer's bindings, instead of the current buffer's.
A keymap can operate as a menu as well as defining bindings for keyboard keys and mouse buttons. Menus are usually actuated with the mouse, but they can function with the keyboard also. If a menu keymap is active for the next input event, that activates the keyboard menu feature.
A keymap acts as a menu if it has an overall prompt string, which is a string that appears as an element of the keymap. (See Format of Keymaps.) The string should describe the purpose of the menu's commands. Emacs displays the overall prompt string as the menu title in some cases, depending on the toolkit (if any) used for displaying menus.12 Keyboard menus also display the overall prompt string.
The easiest way to construct a keymap with a prompt string is to
specify the string as an argument when you call make-keymap,
make-sparse-keymap (see Creating Keymaps), or
define-prefix-command (see Definition of define-prefix-command). If you do not want the keymap to operate as
a menu, don't specify a prompt string for it.
This function returns the overall prompt string of keymap, or
nilif it has none.
The menu's items are the bindings in the keymap. Each binding associates an event type to a definition, but the event types have no significance for the menu appearance. (Usually we use pseudo-events, symbols that the keyboard cannot generate, as the event types for menu item bindings.) The menu is generated entirely from the bindings that correspond in the keymap to these events.
The order of items in the menu is the same as the order of bindings in
the keymap. Since define-key puts new bindings at the front, you
should define the menu items starting at the bottom of the menu and
moving to the top, if you care about the order. When you add an item to
an existing menu, you can specify its position in the menu using
define-key-after (see Modifying Menus).
The simpler (and original) way to define a menu item is to bind some event type (it doesn't matter what event type) to a binding like this:
(item-string . real-binding)
The car, item-string, is the string to be displayed in the menu. It should be short—preferably one to three words. It should describe the action of the command it corresponds to. Note that not all graphical toolkits can display non-ASCII text in menus (it will work for keyboard menus and will work to a large extent with the GTK+ toolkit).
You can also supply a second string, called the help string, as follows:
(item-string help . real-binding)
help specifies a help-echo string to display while the mouse
is on that item in the same way as help-echo text properties
(see Help display).
As far as define-key is concerned, item-string and
help-string are part of the event's binding. However,
lookup-key returns just real-binding, and only
real-binding is used for executing the key.
If real-binding is nil, then item-string appears in
the menu but cannot be selected.
If real-binding is a symbol and has a non-nil
menu-enable property, that property is an expression that
controls whether the menu item is enabled. Every time the keymap is
used to display a menu, Emacs evaluates the expression, and it enables
the menu item only if the expression's value is non-nil. When a
menu item is disabled, it is displayed in a fuzzy fashion, and
cannot be selected.
The menu bar does not recalculate which items are enabled every time you
look at a menu. This is because the X toolkit requires the whole tree
of menus in advance. To force recalculation of the menu bar, call
force-mode-line-update (see Mode Line Format).
An extended-format menu item is a more flexible and also cleaner
alternative to the simple format. You define an event type with a
binding that's a list starting with the symbol menu-item.
For a non-selectable string, the binding looks like this:
(menu-item item-name)
A string starting with two or more dashes specifies a separator line; see Menu Separators.
To define a real menu item which can be selected, the extended format binding looks like this:
(menu-item item-name real-binding
. item-property-list)
Here, item-name is an expression which evaluates to the menu item string. Thus, the string need not be a constant. The third element, real-binding, is the command to execute. The tail of the list, item-property-list, has the form of a property list which contains other information.
Here is a table of the properties that are supported:
:enable form
nil means yes). If the item is not enabled,
you can't really click on it.
:visible form
nil means yes). If the item
does not appear, then the menu is displayed as if this item were
not defined at all.
:help help
help-echo text properties (see Help display).
Note that this must be a constant string, unlike the help-echo
property for text and overlays.
:button (type . selected)
:toggle or
:radio. The cdr, selected, should be a form; the
result of evaluating it says whether this button is currently selected.
A toggle is a menu item which is labeled as either on or off
according to the value of selected. The command itself should
toggle selected, setting it to t if it is nil,
and to nil if it is t. Here is how the menu item
to toggle the debug-on-error flag is defined:
(menu-item "Debug on Error" toggle-debug-on-error
:button (:toggle
. (and (boundp 'debug-on-error)
debug-on-error)))
This works because toggle-debug-on-error is defined as a command
which toggles the variable debug-on-error.
Radio buttons are a group of menu items, in which at any time one
and only one is selected. There should be a variable whose value
says which one is selected at any time. The selected form for
each radio button in the group should check whether the variable has the
right value for selecting that button. Clicking on the button should
set the variable so that the button you clicked on becomes selected.
:key-sequence key-sequence
If you specify the wrong key sequence, it has no effect; before Emacs
displays key-sequence in the menu, it verifies that
key-sequence is really equivalent to this menu item.
:key-sequence nilHowever, if the user has rebound this item's definition to a key
sequence, Emacs ignores the :keys property and finds the keyboard
equivalent anyway.
:keys string
:filter filter-fn
Emacs can call this function at any time that it does redisplay or operates on menu data structures, so you should write it so it can safely be called at any time.
A menu separator is a kind of menu item that doesn't display any text—instead, it divides the menu into subparts with a horizontal line. A separator looks like this in the menu keymap:
(menu-item separator-type)
where separator-type is a string starting with two or more dashes.
In the simplest case, separator-type consists of only dashes.
That specifies the default kind of separator. (For compatibility,
"" and - also count as separators.)
Certain other values of separator-type specify a different style of separator. Here is a table of them:
"--no-line""--space""--single-line""--double-line""--single-dashed-line""--double-dashed-line""--shadow-etched-in""--shadow-etched-out""--shadow-etched-in-dash""--shadow-etched-out-dash""--shadow-double-etched-in""--shadow-double-etched-out""--shadow-double-etched-in-dash""--shadow-double-etched-out-dash"You can also give these names in another style, adding a colon after
the double-dash and replacing each single dash with capitalization of
the following word. Thus, "--:singleLine", is equivalent to
"--single-line".
You can use a longer form to specify keywords such as :enable
and :visible for a menu separator:
(menu-item separator-type nil . item-property-list)
For example:
(menu-item "--" nil :visible (boundp 'foo))
Some systems and display toolkits don't really handle all of these separator types. If you use a type that isn't supported, the menu displays a similar kind of separator that is supported.
Sometimes it is useful to make menu items that use the same
command but with different enable conditions. The best way to do this
in Emacs now is with extended menu items; before that feature existed,
it could be done by defining alias commands and using them in menu
items. Here's an example that makes two aliases for
read-only-mode and gives them different enable conditions:
(defalias 'make-read-only 'read-only-mode)
(put 'make-read-only 'menu-enable '(not buffer-read-only))
(defalias 'make-writable 'read-only-mode)
(put 'make-writable 'menu-enable 'buffer-read-only)
When using aliases in menus, often it is useful to display the
equivalent key bindings for the real command name, not the aliases
(which typically don't have any key bindings except for the menu
itself). To request this, give the alias symbol a non-nil
menu-alias property. Thus,
(put 'make-read-only 'menu-alias t)
(put 'make-writable 'menu-alias t)
causes menu items for make-read-only and make-writable to
show the keyboard bindings for read-only-mode.
The usual way to make a menu keymap produce a menu is to make it the definition of a prefix key. (A Lisp program can explicitly pop up a menu and receive the user's choice—see Pop-Up Menus.)
If the prefix key ends with a mouse event, Emacs handles the menu keymap by popping up a visible menu, so that the user can select a choice with the mouse. When the user clicks on a menu item, the event generated is whatever character or symbol has the binding that brought about that menu item. (A menu item may generate a series of events if the menu has multiple levels or comes from the menu bar.)
It's often best to use a button-down event to trigger the menu. Then the user can select a menu item by releasing the button.
If the menu keymap contains a binding to a nested keymap, the nested keymap specifies a submenu. There will be a menu item, labeled by the nested keymap's item string, and clicking on this item automatically pops up the specified submenu. As a special exception, if the menu keymap contains a single nested keymap and no other menu items, the menu shows the contents of the nested keymap directly, not as a submenu.
However, if Emacs is compiled without X toolkit support, or on text terminals, submenus are not supported. Each nested keymap is shown as a menu item, but clicking on it does not automatically pop up the submenu. If you wish to imitate the effect of submenus, you can do that by giving a nested keymap an item string which starts with `@'. This causes Emacs to display the nested keymap using a separate menu pane; the rest of the item string after the `@' is the pane label. If Emacs is compiled without X toolkit support, or if a menu is displayed on a text terminal, menu panes are not used; in that case, a `@' at the beginning of an item string is omitted when the menu label is displayed, and has no other effect.
When a prefix key ending with a keyboard event (a character or function key) has a definition that is a menu keymap, the keymap operates as a keyboard menu; the user specifies the next event by choosing a menu item with the keyboard.
Emacs displays the keyboard menu with the map's overall prompt
string, followed by the alternatives (the item strings of the map's
bindings), in the echo area. If the bindings don't all fit at once,
the user can type <SPC> to see the next line of alternatives.
Successive uses of <SPC> eventually get to the end of the menu and
then cycle around to the beginning. (The variable
menu-prompt-more-char specifies which character is used for
this; <SPC> is the default.)
When the user has found the desired alternative from the menu, he or she should type the corresponding character—the one whose binding is that alternative.
This variable specifies the character to use to ask to see the next line of a menu. Its initial value is 32, the code for <SPC>.
Here is a complete example of defining a menu keymap. It is the definition of the `Replace' submenu in the `Edit' menu in the menu bar, and it uses the extended menu item format (see Extended Menu Items). First we create the keymap, and give it a name:
(defvar menu-bar-replace-menu (make-sparse-keymap "Replace"))
Next we define the menu items:
(define-key menu-bar-replace-menu [tags-repl-continue]
'(menu-item "Continue Replace" tags-loop-continue
:help "Continue last tags replace operation"))
(define-key menu-bar-replace-menu [tags-repl]
'(menu-item "Replace in tagged files" tags-query-replace
:help "Interactively replace a regexp in all tagged files"))
(define-key menu-bar-replace-menu [separator-replace-tags]
'(menu-item "--"))
;; ...
Note the symbols which the bindings are made for; these appear
inside square brackets, in the key sequence being defined. In some
cases, this symbol is the same as the command name; sometimes it is
different. These symbols are treated as function keys, but they are
not real function keys on the keyboard. They do not affect the
functioning of the menu itself, but they are echoed in the echo area
when the user selects from the menu, and they appear in the output of
where-is and apropos.
The menu in this example is intended for use with the mouse. If a menu is intended for use with the keyboard, that is, if it is bound to a key sequence ending with a keyboard event, then the menu items should be bound to characters or real function keys, that can be typed with the keyboard.
The binding whose definition is ("--") is a separator line.
Like a real menu item, the separator has a key symbol, in this case
separator-replace-tags. If one menu has two separators, they
must have two different key symbols.
Here is how we make this menu appear as an item in the parent menu:
(define-key menu-bar-edit-menu [replace]
(list 'menu-item "Replace" menu-bar-replace-menu))
Note that this incorporates the submenu keymap, which is the value of
the variable menu-bar-replace-menu, rather than the symbol
menu-bar-replace-menu itself. Using that symbol in the parent
menu item would be meaningless because menu-bar-replace-menu is
not a command.
If you wanted to attach the same replace menu to a mouse click, you can do it this way:
(define-key global-map [C-S-down-mouse-1]
menu-bar-replace-menu)
Emacs usually shows a menu bar at the top of each frame.
See Menu Bars. Menu bar items are
subcommands of the fake function key menu-bar, as defined
in the active keymaps.
To add an item to the menu bar, invent a fake function key of your
own (let's call it key), and make a binding for the key sequence
[menu-bar key]. Most often, the binding is a menu keymap,
so that pressing a button on the menu bar item leads to another menu.
When more than one active keymap defines the same function key for the menu bar, the item appears just once. If the user clicks on that menu bar item, it brings up a single, combined menu containing all the subcommands of that item—the global subcommands, the local subcommands, and the minor mode subcommands.
The variable overriding-local-map is normally ignored when
determining the menu bar contents. That is, the menu bar is computed
from the keymaps that would be active if overriding-local-map
were nil. See Active Keymaps.
Here's an example of setting up a menu bar item:
;; Make a menu keymap (with a prompt string) ;; and make it the menu bar item's definition. (define-key global-map [menu-bar words] (cons "Words" (make-sparse-keymap "Words"))) ;; Define specific subcommands in this menu. (define-key global-map [menu-bar words forward] '("Forward word" . forward-word)) (define-key global-map [menu-bar words backward] '("Backward word" . backward-word))
A local keymap can cancel a menu bar item made by the global keymap by
rebinding the same fake function key with undefined as the
binding. For example, this is how Dired suppresses the `Edit' menu
bar item:
(define-key dired-mode-map [menu-bar edit] 'undefined)
Here, edit is the fake function key used by the global map for
the `Edit' menu bar item. The main reason to suppress a global
menu bar item is to regain space for mode-specific items.
Normally the menu bar shows global items followed by items defined by the local maps.
This variable holds a list of fake function keys for items to display at the end of the menu bar rather than in normal sequence. The default value is
(help-menu); thus, the `Help' menu item normally appears at the end of the menu bar, following local menu items.
This normal hook is run by redisplay to update the menu bar contents, before redisplaying the menu bar. You can use it to update menus whose contents should vary. Since this hook is run frequently, we advise you to ensure that the functions it calls do not take much time in the usual case.
Next to every menu bar item, Emacs displays a key binding that runs
the same command (if such a key binding exists). This serves as a
convenient hint for users who do not know the key binding. If a
command has multiple bindings, Emacs normally displays the first one
it finds. You can specify one particular key binding by assigning an
:advertised-binding symbol property to the command. See Keys in Documentation.
A tool bar is a row of clickable icons at the top of a frame, just below the menu bar. See Tool Bars. Emacs normally shows a tool bar on graphical displays.
On each frame, the frame parameter tool-bar-lines controls
how many lines' worth of height to reserve for the tool bar. A zero
value suppresses the tool bar. If the value is nonzero, and
auto-resize-tool-bars is non-nil, the tool bar expands
and contracts automatically as needed to hold the specified contents.
If the value is grow-only, the tool bar expands automatically,
but does not contract automatically.
The tool bar contents are controlled by a menu keymap attached to a
fake function key called tool-bar (much like the way the menu
bar is controlled). So you define a tool bar item using
define-key, like this:
(define-key global-map [tool-bar key] item)
where key is a fake function key to distinguish this item from other items, and item is a menu item key binding (see Extended Menu Items), which says how to display this item and how it behaves.
The usual menu keymap item properties, :visible,
:enable, :button, and :filter, are useful in
tool bar bindings and have their normal meanings. The real-binding
in the item must be a command, not a keymap; in other words, it does not
work to define a tool bar icon as a prefix key.
The :help property specifies a help-echo string to display
while the mouse is on that item. This is displayed in the same way as
help-echo text properties (see Help display).
In addition, you should use the :image property;
this is how you specify the image to display in the tool bar:
:image image
The GTK+ and NS versions of Emacs ignores items 1 to 3, because disabled and/or deselected images are autocomputed from item 0.
If image is a single image specification, Emacs draws the tool bar button in disabled state by applying an edge-detection algorithm to the image.
The :rtl property specifies an alternative image to use for
right-to-left languages. Only the GTK+ version of Emacs supports this
at present.
Like the menu bar, the tool bar can display separators (see Menu Separators). Tool bar separators are vertical rather than
horizontal, though, and only a single style is supported. They are
represented in the tool bar keymap by (menu-item "--") entries;
properties like :visible are not supported for tool bar
separators. Separators are rendered natively in GTK+ and Nextstep
tool bars; in the other cases, they are rendered using an image of a
vertical line.
The default tool bar is defined so that items specific to editing do not
appear for major modes whose command symbol has a mode-class
property of special (see Major Mode Conventions). Major
modes may add items to the global bar by binding [tool-bar
foo] in their local map. It makes sense for some major modes to
replace the default tool bar items completely, since not many can be
accommodated conveniently, and the default bindings make this easy by
using an indirection through tool-bar-map.
By default, the global map binds
[tool-bar]as follows:(global-set-key [tool-bar] `(menu-item ,(purecopy "tool bar") ignore :filter tool-bar-make-keymap))The function
tool-bar-make-keymap, in turn, derives the actual tool bar map dynamically from the value of the variabletool-bar-map. Hence, you should normally adjust the default (global) tool bar by changing that map. Some major modes, such as Info mode, completely replace the global tool bar by makingtool-bar-mapbuffer-local and setting it to a different keymap.
There are two convenience functions for defining tool bar items, as follows.
This function adds an item to the tool bar by modifying
tool-bar-map. The image to use is defined by icon, which is the base name of an XPM, XBM or PBM image file to be located byfind-image. Given a value `"exit"', say, exit.xpm, exit.pbm and exit.xbm would be searched for in that order on a color display. On a monochrome display, the search order is `.pbm', `.xbm' and `.xpm'. The binding to use is the command def, and key is the fake function key symbol in the prefix keymap. The remaining arguments props are additional property list elements to add to the menu item specification.To define items in some local map, bind
tool-bar-mapwithletaround calls of this function:(defvar foo-tool-bar-map (let ((tool-bar-map (make-sparse-keymap))) (tool-bar-add-item ...) ... tool-bar-map))
This function is a convenience for defining tool bar items which are consistent with existing menu bar bindings. The binding of command is looked up in the menu bar in map (default
global-map) and modified to add an image specification for icon, which is found in the same way as bytool-bar-add-item. The resulting binding is then placed intool-bar-map, so use this function only for global tool bar items.map must contain an appropriate keymap bound to
[menu-bar]. The remaining arguments props are additional property list elements to add to the menu item specification.
This function is used for making non-global tool bar items. Use it like
tool-bar-add-item-from-menuexcept that in-map specifies the local map to make the definition in. The argument from-map is like the map argument oftool-bar-add-item-from-menu.
If this variable is non-
nil, the tool bar automatically resizes to show all defined tool bar items—but not larger than a quarter of the frame's height.If the value is
grow-only, the tool bar expands automatically, but does not contract automatically. To contract the tool bar, the user has to redraw the frame by entering C-l.If Emacs is built with GTK or Nextstep, the tool bar can only show one line, so this variable has no effect.
If this variable is non-
nil, tool bar items display in raised form when the mouse moves over them.
This variable specifies an extra margin to add around tool bar items. The value is an integer, a number of pixels. The default is 4.
This variable specifies the shadow width for tool bar items. The value is an integer, a number of pixels. The default is 1.
This variable specifies the height of the border drawn below the tool bar area. An integer specifies height as a number of pixels. If the value is one of
internal-border-width(the default) orborder-width, the tool bar border height corresponds to the corresponding frame parameter.
You can define a special meaning for clicking on a tool bar item with the shift, control, meta, etc., modifiers. You do this by setting up additional items that relate to the original item through the fake function keys. Specifically, the additional items should use the modified versions of the same fake function key used to name the original item.
Thus, if the original item was defined this way,
(define-key global-map [tool-bar shell]
'(menu-item "Shell" shell
:image (image :type xpm :file "shell.xpm")))
then here is how you can define clicking on the same tool bar image with the shift modifier:
(define-key global-map [tool-bar S-shell] 'some-command)
See Function Keys, for more information about how to add modifiers to function keys.
When you insert a new item in an existing menu, you probably want to
put it in a particular place among the menu's existing items. If you
use define-key to add the item, it normally goes at the front of
the menu. To put it elsewhere in the menu, use define-key-after:
Define a binding in map for key, with value binding, just like
define-key, but position the binding in map after the binding for the event after. The argument key should be of length one—a vector or string with just one element. But after should be a single event type—a symbol or a character, not a sequence. The new binding goes after the binding for after. If after istor is omitted, then the new binding goes last, at the end of the keymap. However, new bindings are added before any inherited keymap.Here is an example:
(define-key-after my-menu [drink] '("Drink" . drink-command) 'eat)makes a binding for the fake function key <DRINK> and puts it right after the binding for <EAT>.
Here is how to insert an item called `Work' in the `Signals' menu of Shell mode, after the item
break:(define-key-after (lookup-key shell-mode-map [menu-bar signals]) [work] '("Work" . work-command) 'break)
The following macro provides a convenient way to define pop-up menus and/or menu bar menus.
This macro defines a pop-up menu and/or menu bar submenu, whose contents are given by menu.
If symbol is non-
nil, it should be a symbol; then this macro defines symbol as a function for popping up the menu (see Pop-Up Menus), with doc as its documentation string. symbol should not be quoted.Regardless of the value of symbol, if maps is a keymap, the menu is added to that keymap, as a top-level menu for the menu bar (see Menu Bar). It can also be a list of keymaps, in which case the menu is added separately to each of those keymaps.
The first element of menu must be a string, which serves as the menu label. It may be followed by any number of the following keyword-argument pairs:
:filterfunction- function must be a function which, if called with one argument—the list of the other menu items—returns the actual items to be displayed in the menu.
:visibleinclude- include is an expression; if it evaluates to
nil, the menu is made invisible.:includedis an alias for:visible.
:activeenable- enable is an expression; if it evaluates to
nil, the menu is not selectable.:enableis an alias for:active.The remaining elements in menu are menu items.
A menu item can be a vector of three elements,
[name callback enable]. name is the menu item name (a string). callback is a command to run, or an expression to evaluate, when the item is chosen. enable is an expression; if it evaluates tonil, the item is disabled for selection.Alternatively, a menu item may have the form:
[ name callback [ keyword arg ]... ]where name and callback have the same meanings as above, and each optional keyword and arg pair should be one of the following:
:keyskeys- keys is a keyboard equivalent to the menu item (a string). This is normally not needed, as keyboard equivalents are computed automatically. keys is expanded with
substitute-command-keysbefore it is displayed (see Keys in Documentation).
:key-sequencekeys- keys is a hint for speeding up Emacs's first display of the menu. It should be
nilif you know that the menu item has no keyboard equivalent; otherwise it should be a string or vector specifying a keyboard equivalent for the menu item.
:activeenable- enable is an expression; if it evaluates to
nil, the item is make unselectable..:enableis an alias for:active.
:visibleinclude- include is an expression; if it evaluates to
nil, the item is made invisible.:includedis an alias for:visible.
:labelform- form is an expression that is evaluated to obtain a value which serves as the menu item's label (the default is name).
:suffixform- form is an expression that is dynamically evaluated and whose value is concatenated with the menu entry's label.
:stylestyle- style is a symbol describing the type of menu item; it should be
toggle(a checkbox), orradio(a radio button), or anything else (meaning an ordinary menu item).
:selectedselected- selected is an expression; the checkbox or radio button is selected whenever the expression's value is non-
nil.
:helphelp- help is a string describing the menu item.
Alternatively, a menu item can be a string. Then that string appears in the menu as unselectable text. A string consisting of dashes is displayed as a separator (see Menu Separators).
Alternatively, a menu item can be a list with the same format as menu. This is a submenu.
Here is an example of using easy-menu-define to define a menu
similar to the one defined in the example in Menu Bar:
(easy-menu-define words-menu global-map
"Menu for word navigation commands."
'("Words"
["Forward word" forward-word]
["Backward word" backward-word]))
A mode is a set of definitions that customize Emacs and can be turned on and off while you edit. There are two varieties of modes: major modes, which are mutually exclusive and used for editing particular kinds of text, and minor modes, which provide features that users can enable individually.
This chapter describes how to write both major and minor modes, how to indicate them in the mode line, and how they run hooks supplied by the user. For related topics such as keymaps and syntax tables, see Keymaps, and Syntax Tables.
A hook is a variable where you can store a function or functions to be called on a particular occasion by an existing program. Emacs provides hooks for the sake of customization. Most often, hooks are set up in the init file (see Init File), but Lisp programs can set them also. See Standard Hooks, for a list of some standard hook variables.
Most of the hooks in Emacs are normal hooks. These variables contain lists of functions to be called with no arguments. By convention, whenever the hook name ends in `-hook', that tells you it is normal. We try to make all hooks normal, as much as possible, so that you can use them in a uniform way.
Every major mode command is supposed to run a normal hook called the
mode hook as one of the last steps of initialization. This makes
it easy for a user to customize the behavior of the mode, by overriding
the buffer-local variable assignments already made by the mode. Most
minor mode functions also run a mode hook at the end. But hooks are
used in other contexts too. For example, the hook suspend-hook
runs just before Emacs suspends itself (see Suspending Emacs).
The recommended way to add a hook function to a hook is by calling
add-hook (see Setting Hooks). The hook functions may be any
of the valid kinds of functions that funcall accepts (see What Is a Function). Most normal hook variables are initially void;
add-hook knows how to deal with this. You can add hooks either
globally or buffer-locally with add-hook.
If the hook variable's name does not end with `-hook', that
indicates it is probably an abnormal hook. That means the hook
functions are called with arguments, or their return values are used
in some way. The hook's documentation says how the functions are
called. You can use add-hook to add a function to an abnormal
hook, but you must write the function to follow the hook's calling
convention. By convention, abnormal hook names end in `-functions'.
If the variable's name ends in `-function', then its value is
just a single function, not a list of functions. add-hook cannot be
used to modify such a single function hook, and you have to use
add-function instead (see Advising Functions).
In this section, we document the run-hooks function, which is
used to run a normal hook. We also document the functions for running
various kinds of abnormal hooks.
This function takes one or more normal hook variable names as arguments, and runs each hook in turn. Each argument should be a symbol that is a normal hook variable. These arguments are processed in the order specified.
If a hook variable has a non-
nilvalue, that value should be a list of functions.run-hookscalls all the functions, one by one, with no arguments.The hook variable's value can also be a single function—either a lambda expression or a symbol with a function definition—which
run-hookscalls. But this usage is obsolete.If the hook variable is buffer-local, the buffer-local variable will be used instead of the global variable. However, if the buffer-local variable contains the element
t, the global hook variable will be run as well.
This function runs an abnormal hook by calling all the hook functions in hook, passing each one the arguments args.
This function runs an abnormal hook by calling each hook function in turn, stopping if one of them fails by returning
nil. Each hook function is passed the arguments args. If this function stops because one of the hook functions fails, it returnsnil; otherwise it returns a non-nilvalue.
This function runs an abnormal hook by calling each hook function, stopping if one of them succeeds by returning a non-
nilvalue. Each hook function is passed the arguments args. If this function stops because one of the hook functions returns a non-nilvalue, it returns that value; otherwise it returnsnil.
Here's an example that uses a mode hook to turn on Auto Fill mode when in Lisp Interaction mode:
(add-hook 'lisp-interaction-mode-hook 'auto-fill-mode)
This function is the handy way to add function function to hook variable hook. You can use it for abnormal hooks as well as for normal hooks. function can be any Lisp function that can accept the proper number of arguments for hook. For example,
(add-hook 'text-mode-hook 'my-text-hook-function)adds
my-text-hook-functionto the hook calledtext-mode-hook.If function is already present in hook (comparing using
equal), thenadd-hookdoes not add it a second time.If function has a non-
nilpropertypermanent-local-hook, thenkill-all-local-variables(or changing major modes) won't delete it from the hook variable's local value.For a normal hook, hook functions should be designed so that the order in which they are executed does not matter. Any dependence on the order is asking for trouble. However, the order is predictable: normally, function goes at the front of the hook list, so it is executed first (barring another
add-hookcall). If the optional argument append is non-nil, the new hook function goes at the end of the hook list and is executed last.
add-hookcan handle the cases where hook is void or its value is a single function; it sets or changes the value to a list of functions.If local is non-
nil, that says to add function to the buffer-local hook list instead of to the global hook list. This makes the hook buffer-local and addstto the buffer-local value. The latter acts as a flag to run the hook functions in the default value as well as in the local value.
This function removes function from the hook variable hook. It compares function with elements of hook using
equal, so it works for both symbols and lambda expressions.If local is non-
nil, that says to remove function from the buffer-local hook list instead of from the global hook list.
Major modes specialize Emacs for editing particular kinds of text. Each buffer has one major mode at a time. Every major mode is associated with a major mode command, whose name should end in `-mode'. This command takes care of switching to that mode in the current buffer, by setting various buffer-local variables such as a local keymap. See Major Mode Conventions.
The least specialized major mode is called Fundamental mode, which has no mode-specific definitions or variable settings.
This is the major mode command for Fundamental mode. Unlike other mode commands, it does not run any mode hooks (see Major Mode Conventions), since you are not supposed to customize this mode.
The easiest way to write a major mode is to use the macro
define-derived-mode, which sets up the new mode as a variant of
an existing major mode. See Derived Modes. We recommend using
define-derived-mode even if the new mode is not an obvious
derivative of another mode, as it automatically enforces many coding
conventions for you. See Basic Major Modes, for common modes to
derive from.
The standard GNU Emacs Lisp directory tree contains the code for several major modes, in files such as text-mode.el, texinfo.el, lisp-mode.el, and rmail.el. You can study these libraries to see how modes are written.
The buffer-local value of this variable holds the symbol for the current major mode. Its default value holds the default major mode for new buffers. The standard default value is
fundamental-mode.If the default value is
nil, then whenever Emacs creates a new buffer via a command such as C-x b (switch-to-buffer), the new buffer is put in the major mode of the previously current buffer. As an exception, if the major mode of the previous buffer has amode-classsymbol property with valuespecial, the new buffer is put in Fundamental mode (see Major Mode Conventions).
The code for every major mode should follow various coding conventions, including conventions for local keymap and syntax table initialization, function and variable names, and hooks.
If you use the define-derived-mode macro, it will take care of
many of these conventions automatically. See Derived Modes. Note
also that Fundamental mode is an exception to many of these conventions,
because it represents the default state of Emacs.
The following list of conventions is only partial. Each major mode should aim for consistency in general with other Emacs major modes, as this makes Emacs as a whole more coherent. It is impossible to list here all the possible points where this issue might come up; if the Emacs developers point out an area where your major mode deviates from the usual conventions, please make it compatible.
The documentation string may include the special documentation substrings, `\[command]', `\{keymap}', and `\<keymap>', which allow the help display to adapt automatically to the user's own key bindings. See Keys in Documentation.
kill-all-local-variables. This runs the normal hook
change-major-mode-hook, then gets rid of the buffer-local
variables of the major mode previously in effect. See Creating Buffer-Local.
major-mode to the
major mode command symbol. This is how describe-mode discovers
which documentation to print.
mode-name to the
“pretty” name of the mode, usually a string (but see Mode Line Data, for other possible forms). The name of the mode appears
in the mode line.
indent-line-function
to a suitable function, and probably customize other variables
for indentation. See Auto-Indentation.
use-local-map to install this local map. See Active Keymaps, for more information.
This keymap should be stored permanently in a global variable named
modename-mode-map. Normally the library that defines the
mode sets this variable.
See Tips for Defining, for advice about how to write the code to set up the mode's keymap variable.
A major mode can also rebind the keys M-n, M-p and M-s. The bindings for M-n and M-p should normally be some kind of moving forward and backward, but this does not necessarily mean cursor motion.
It is legitimate for a major mode to rebind a standard key sequence if it provides a command that does the same job in a way better suited to the text this mode is used for. For example, a major mode for editing a programming language might redefine C-M-a to move to the beginning of a function in a way that works better for that language.
It is also legitimate for a major mode to rebind a standard key sequence whose standard meaning is rarely useful in that mode. For instance, minibuffer modes rebind M-r, whose standard meaning is rarely of any use in the minibuffer. Major modes such as Dired or Rmail that do not allow self-insertion of text can reasonably redefine letters and other printing characters as special commands.
-mode-syntax-table. See Syntax Tables.
-mode-abbrev-table. If the
major mode command defines any abbrevs itself, it should pass t
for the system-flag argument to define-abbrev.
See Defining Abbrevs.
font-lock-defaults (see Font Lock Mode).
imenu-generic-expression, for the two variables
imenu-prev-index-position-function and
imenu-extract-index-name-function, or for the variable
imenu-create-index-function (see Imenu).
eldoc-documentation-function to tell ElDoc mode how to handle
this mode.
completion-at-point-functions. See Completion in Buffers.
make-local-variable in the major mode command, not
make-variable-buffer-local. The latter function would make the
variable local to every buffer in which it is subsequently set, which
would affect buffers that do not use this mode. It is undesirable for a
mode to have such global effects. See Buffer-Local Variables.
With rare exceptions, the only reasonable way to use
make-variable-buffer-local in a Lisp package is for a variable
which is used only within that package. Using it on a variable used by
other packages would interfere with them.
-mode-hook. The very last thing the major mode command
should do is to call run-mode-hooks. This runs the normal
hook change-major-mode-after-body-hook, the mode hook,
and then the normal hook after-change-major-mode-hook.
See Mode Hooks.
define-derived-mode
macro, but this is not required. Such a mode should call the parent
mode command inside a delay-mode-hooks form. (Using
define-derived-mode does this automatically.) See Derived Modes, and Mode Hooks.
change-major-mode-hook (see Creating Buffer-Local).
mode-class with value special, put on as
follows:
(put 'funny-mode 'mode-class 'special)
This tells Emacs that new buffers created while the current buffer is in
Funny mode should not be put in Funny mode, even though the default
value of major-mode is nil. By default, the value of
nil for major-mode means to use the current buffer's major
mode when creating new buffers (see Auto Major Mode), but with such
special modes, Fundamental mode is used instead. Modes such as
Dired, Rmail, and Buffer List use this feature.
The function view-buffer does not enable View mode in buffers
whose mode-class is special, because such modes usually provide their
own View-like bindings.
The define-derived-mode macro automatically marks the derived
mode as special if the parent mode is special. Special mode is a
convenient parent for such modes to inherit from; See Basic Major Modes.
auto-mode-alist to select
the mode for those file names (see Auto Major Mode). If you
define the mode command to autoload, you should add this element in
the same file that calls autoload. If you use an autoload
cookie for the mode command, you can also use an autoload cookie for
the form that adds the element (see autoload cookie). If you do
not autoload the mode command, it is sufficient to add the element in
the file that contains the mode definition.
defvar or defcustom to set mode-related
variables, so that they are not reinitialized if they already have a
value (see Defining Variables).
When Emacs visits a file, it automatically selects a major mode for the buffer based on information in the file name or in the file itself. It also processes local variables specified in the file text.
This function establishes the proper major mode and buffer-local variable bindings for the current buffer. First it calls
set-auto-mode(see below), then it runshack-local-variablesto parse, and bind or evaluate as appropriate, the file's local variables (see File Local Variables).If the find-file argument to
normal-modeis non-nil,normal-modeassumes that thefind-filefunction is calling it. In this case, it may process local variables in the `-*-' line or at the end of the file. The variableenable-local-variablescontrols whether to do so. See Local Variables in Files, for the syntax of the local variables section of a file.If you run
normal-modeinteractively, the argument find-file is normallynil. In this case,normal-modeunconditionally processes any file local variables.The function calls
set-auto-modeto choose a major mode. If this does not specify a mode, the buffer stays in the major mode determined by the default value ofmajor-mode(see below).
normal-modeusescondition-casearound the call to the major mode command, so errors are caught and reported as a `File mode specification error', followed by the original error message.
This function selects the major mode that is appropriate for the current buffer. It bases its decision (in order of precedence) on the `-*-' line, on any `mode:' local variable near the end of a file, on the `#!' line (using
interpreter-mode-alist), on the text at the beginning of the buffer (usingmagic-mode-alist), and finally on the visited file name (usingauto-mode-alist). See How Major Modes are Chosen. Ifenable-local-variablesisnil,set-auto-modedoes not check the `-*-' line, or near the end of the file, for any mode tag.There are some file types where it is not appropriate to scan the file contents for a mode specifier. For example, a tar archive may happen to contain, near the end of the file, a member file that has a local variables section specifying a mode for that particular file. This should not be applied to the containing tar file. Similarly, a tiff image file might just happen to contain a first line that seems to match the `-*-' pattern. For these reasons, both these file extensions are members of the list
inhibit-local-variables-regexps. Add patterns to this list to prevent Emacs searching them for local variables of any kind (not just mode specifiers).If keep-mode-if-same is non-
nil, this function does not call the mode command if the buffer is already in the proper major mode. For instance,set-visited-file-namesets this totto avoid killing buffer local variables that the user may have set.
This function sets the major mode of buffer to the default value of
major-mode; if that isnil, it uses the current buffer's major mode (if that is suitable). As an exception, if buffer's name is *scratch*, it sets the mode toinitial-major-mode.The low-level primitives for creating buffers do not use this function, but medium-level commands such as
switch-to-bufferandfind-file-noselectuse it whenever they create buffers.
The value of this variable determines the major mode of the initial *scratch* buffer. The value should be a symbol that is a major mode command. The default value is
lisp-interaction-mode.
This variable specifies major modes to use for scripts that specify a command interpreter in a `#!' line. Its value is an alist with elements of the form
(regexp.mode); this says to use mode mode if the file specifies an interpreter which matches\\`regexp\\'. For example, one of the default elements is("python[0-9.]*" . python-mode).
This variable's value is an alist with elements of the form
(regexp.function), where regexp is a regular expression and function is a function ornil. After visiting a file,set-auto-modecalls function if the text at the beginning of the buffer matches regexp and function is non-nil; if function isnil,auto-mode-alistgets to decide the mode.
This works like
magic-mode-alist, except that it is handled only ifauto-mode-alistdoes not specify a mode for this file.
This variable contains an association list of file name patterns (regular expressions) and corresponding major mode commands. Usually, the file name patterns test for suffixes, such as `.el' and `.c', but this need not be the case. An ordinary element of the alist looks like
(regexp.mode-function).For example,
(("\\`/tmp/fol/" . text-mode) ("\\.texinfo\\'" . texinfo-mode) ("\\.texi\\'" . texinfo-mode) ("\\.el\\'" . emacs-lisp-mode) ("\\.c\\'" . c-mode) ("\\.h\\'" . c-mode) ...)When you visit a file whose expanded file name (see File Name Expansion), with version numbers and backup suffixes removed using
file-name-sans-versions(see File Name Components), matches a regexp,set-auto-modecalls the corresponding mode-function. This feature enables Emacs to select the proper major mode for most files.If an element of
auto-mode-alisthas the form(regexp functiont), then after calling function, Emacs searchesauto-mode-alistagain for a match against the portion of the file name that did not match before. This feature is useful for uncompression packages: an entry of the form("\\.gz\\'"functiont)can uncompress the file and then put the uncompressed file in the proper mode according to the name sans `.gz'.Here is an example of how to prepend several pattern pairs to
auto-mode-alist. (You might use this sort of expression in your init file.)(setq auto-mode-alist (append ;; File name (within directory) starts with a dot. '(("/\\.[^/]*\\'" . fundamental-mode) ;; File name has no dot. ("/[^\\./]*\\'" . fundamental-mode) ;; File name ends in `.C'. ("\\.C\\'" . c++-mode)) auto-mode-alist))
The describe-mode function provides information about major
modes. It is normally bound to C-h m. It uses the value of the
variable major-mode (see Major Modes), which is why every
major mode command needs to set that variable.
This command displays the documentation of the current buffer's major mode and minor modes. It uses the
documentationfunction to retrieve the documentation strings of the major and minor mode commands (see Accessing Documentation).If called from Lisp with a non-
nilbuffer argument, this function displays the documentation for that buffer's major and minor modes, rather than those of the current buffer.
The recommended way to define a new major mode is to derive it from an
existing one using define-derived-mode. If there is no closely
related mode, you should inherit from either text-mode,
special-mode, or prog-mode. See Basic Major Modes. If
none of these are suitable, you can inherit from fundamental-mode
(see Major Modes).
This macro defines variant as a major mode command, using name as the string form of the mode name. variant and parent should be unquoted symbols.
The new command variant is defined to call the function parent, then override certain aspects of that parent mode:
- The new mode has its own sparse keymap, named variant
-map.define-derived-modemakes the parent mode's keymap the parent of the new map, unless variant-mapis already set and already has a parent.- The new mode has its own syntax table, kept in the variable variant
-syntax-table, unless you override this using the:syntax-tablekeyword (see below).define-derived-modemakes the parent mode's syntax-table the parent of variant-syntax-table, unless the latter is already set and already has a parent different from the standard syntax table.- The new mode has its own abbrev table, kept in the variable variant
-abbrev-table, unless you override this using the:abbrev-tablekeyword (see below).- The new mode has its own mode hook, variant
-hook. It runs this hook, after running the hooks of its ancestor modes, withrun-mode-hooks, as the last thing it does. See Mode Hooks.In addition, you can specify how to override other aspects of parent with body. The command variant evaluates the forms in body after setting up all its usual overrides, just before running the mode hooks.
If parent has a non-
nilmode-classsymbol property, thendefine-derived-modesets themode-classproperty of variant to the same value. This ensures, for example, that if parent is a special mode, then variant is also a special mode (see Major Mode Conventions).You can also specify
nilfor parent. This gives the new mode no parent. Thendefine-derived-modebehaves as described above, but, of course, omits all actions connected with parent.The argument docstring specifies the documentation string for the new mode.
define-derived-modeadds some general information about the mode's hook, followed by the mode's keymap, at the end of this documentation string. If you omit docstring,define-derived-modegenerates a documentation string.The keyword-args are pairs of keywords and values. The values are evaluated. The following keywords are currently supported:
:syntax-table- You can use this to explicitly specify a syntax table for the new mode. If you specify a
nilvalue, the new mode uses the same syntax table as parent, or the standard syntax table if parent isnil. (Note that this does not follow the convention used for non-keyword arguments that anilvalue is equivalent with not specifying the argument.)
:abbrev-table- You can use this to explicitly specify an abbrev table for the new mode. If you specify a
nilvalue, the new mode uses the same abbrev table as parent, orfundamental-mode-abbrev-tableif parent isnil. (Again, anilvalue is not equivalent to not specifying this keyword.)
:group- If this is specified, the value should be the customization group for this mode. (Not all major modes have one.) Only the (still experimental and unadvertised) command
customize-modecurrently uses this.define-derived-modedoes not automatically define the specified customization group.Here is a hypothetical example:
(define-derived-mode hypertext-mode text-mode "Hypertext" "Major mode for hypertext. \\{hypertext-mode-map}" (setq case-fold-search nil)) (define-key hypertext-mode-map [down-mouse-3] 'do-hyper-link)Do not write an
interactivespec in the definition;define-derived-modedoes that automatically.
This function returns non-
nilif the current major mode is derived from any of the major modes given by the symbols modes.
Apart from Fundamental mode, there are three major modes that other major modes commonly derive from: Text mode, Prog mode, and Special mode. While Text mode is useful in its own right (e.g., for editing files ending in .txt), Prog mode and Special mode exist mainly to let other modes derive from them.
As far as possible, new major modes should be derived, either directly
or indirectly, from one of these three modes. One reason is that this
allows users to customize a single mode hook
(e.g., prog-mode-hook) for an entire family of relevant modes
(e.g., all programming language modes).
Text mode is a major mode for editing human languages. It defines the `"' and `\' characters as having punctuation syntax (see Syntax Class Table), and binds M-<TAB> to
ispell-complete-word(see Spelling).An example of a major mode derived from Text mode is HTML mode. See SGML and HTML Modes.
Prog mode is a basic major mode for buffers containing programming language source code. Most of the programming language major modes built into Emacs are derived from it.
Prog mode binds
parse-sexp-ignore-commentstot(see Motion via Parsing) andbidi-paragraph-directiontoleft-to-right(see Bidirectional Display).
Special mode is a basic major mode for buffers containing text that is produced specially by Emacs, rather than directly from a file. Major modes derived from Special mode are given a
mode-classproperty ofspecial(see Major Mode Conventions).Special mode sets the buffer to read-only. Its keymap defines several common bindings, including q for
quit-windowand g forrevert-buffer(see Reverting).An example of a major mode derived from Special mode is Buffer Menu mode, which is used by the *Buffer List* buffer. See Listing Existing Buffers.
In addition, modes for buffers of tabulated data can inherit from Tabulated List mode, which is in turn derived from Special mode. See Tabulated List Mode.
Every major mode command should finish by running the mode-independent
normal hook change-major-mode-after-body-hook, its mode hook,
and the normal hook after-change-major-mode-hook.
It does this by calling run-mode-hooks. If the major mode is a
derived mode, that is if it calls another major mode (the parent mode)
in its body, it should do this inside delay-mode-hooks so that
the parent won't run these hooks itself. Instead, the derived mode's
call to run-mode-hooks runs the parent's mode hook too.
See Major Mode Conventions.
Emacs versions before Emacs 22 did not have delay-mode-hooks.
Versions before 24 did not have change-major-mode-after-body-hook.
When user-implemented major modes do not use run-mode-hooks and
have not been updated to use these newer features, they won't entirely
follow these conventions: they may run the parent's mode hook too early,
or fail to run after-change-major-mode-hook. If you encounter
such a major mode, please correct it to follow these conventions.
When you defined a major mode using define-derived-mode, it
automatically makes sure these conventions are followed. If you
define a major mode “by hand”, not using define-derived-mode,
use the following functions to handle these conventions automatically.
Major modes should run their mode hook using this function. It is similar to
run-hooks(see Hooks), but it also runschange-major-mode-after-body-hookandafter-change-major-mode-hook.When this function is called during the execution of a
delay-mode-hooksform, it does not run the hooks immediately. Instead, it arranges for the next call torun-mode-hooksto run them.
When one major mode command calls another, it should do so inside of
delay-mode-hooks.This macro executes body, but tells all
run-mode-hookscalls during the execution of body to delay running their hooks. The hooks will actually run during the next call torun-mode-hooksafter the end of thedelay-mode-hooksconstruct.
This is a normal hook run by
run-mode-hooks. It is run before the mode hooks.
This is a normal hook run by
run-mode-hooks. It is run at the very end of every properly-written major mode command.
Tabulated List mode is a major mode for displaying tabulated data, i.e., data consisting of entries, each entry occupying one row of text with its contents divided into columns. Tabulated List mode provides facilities for pretty-printing rows and columns, and sorting the rows according to the values in each column. It is derived from Special mode (see Basic Major Modes).
Tabulated List mode is intended to be used as a parent mode by a more specialized major mode. Examples include Process Menu mode (see Process Information) and Package Menu mode (see Package Menu).
Such a derived mode should use define-derived-mode in the usual
way, specifying tabulated-list-mode as the second argument
(see Derived Modes). The body of the define-derived-mode
form should specify the format of the tabulated data, by assigning
values to the variables documented below; optionally, it can then call
the function tabulated-list-init-header, which will populate a
header with the names of the columns.
The derived mode should also define a listing command. This,
not the mode command, is what the user calls (e.g., M-x
list-processes). The listing command should create or switch to a
buffer, turn on the derived mode, specify the tabulated data, and
finally call tabulated-list-print to populate the buffer.
This buffer-local variable specifies the format of the Tabulated List data. Its value should be a vector. Each element of the vector represents a data column, and should be a list
(name width sort), where
- name is the column's name (a string).
- width is the width to reserve for the column (an integer). This is meaningless for the last column, which runs to the end of each line.
- sort specifies how to sort entries by the column. If
nil, the column cannot be used for sorting. Ift, the column is sorted by comparing string values. Otherwise, this should be a predicate function forsort(see Rearrangement), which accepts two arguments with the same form as the elements oftabulated-list-entries(see below).
This buffer-local variable specifies the entries displayed in the Tabulated List buffer. Its value should be either a list, or a function.
If the value is a list, each list element corresponds to one entry, and should have the form
(idcontents), where
- id is either
nil, or a Lisp object that identifies the entry. If the latter, the cursor stays on the same entry when re-sorting entries. Comparison is done withequal.- contents is a vector with the same number of elements as
tabulated-list-format. Each vector element is either a string, which is inserted into the buffer as-is, or a list(label.properties), which means to insert a text button by callinginsert-text-buttonwith label and properties as arguments (see Making Buttons).There should be no newlines in any of these strings.
Otherwise, the value should be a function which returns a list of the above form when called with no arguments.
This normal hook is run prior to reverting a Tabulated List buffer. A derived mode can add a function to this hook to recompute
tabulated-list-entries.
The value of this variable is the function called to insert an entry at point, including its terminating newline. The function should accept two arguments, id and contents, having the same meanings as in
tabulated-list-entries. The default value is a function which inserts an entry in a straightforward way; a mode which uses Tabulated List mode in a more complex way can specify another function.
The value of this variable specifies the current sort key for the Tabulated List buffer. If it is
nil, no sorting is done. Otherwise, it should have the form(name.flip), where name is a string matching one of the column names intabulated-list-format, and flip, if non-nil, means to invert the sort order.
This function computes and sets
header-line-formatfor the Tabulated List buffer (see Header Lines), and assigns a keymap to the header line to allow sort entries by clicking on column headers.Modes derived from Tabulated List mode should call this after setting the above variables (in particular, only after setting
tabulated-list-format).
This function populates the current buffer with entries. It should be called by the listing command. It erases the buffer, sorts the entries specified by
tabulated-list-entriesaccording totabulated-list-sort-key, then calls the function specified bytabulated-list-printerto insert each entry.If the optional argument remember-pos is non-
nil, this function looks for the id element on the current line, if any, and tries to move to that entry after all the entries are (re)inserted.If the optional argument update is non-
nil, this function will only erase or add entries that have changed since the last print. This is several times faster if most entries haven't changed since the last time this function was called. The only difference in outcome is that tags placed viatabulated-list-put-tagwill not be removed from entries that haven't changed (normally all tags are removed).
Generic modes are simple major modes with basic support for
comment syntax and Font Lock mode. To define a generic mode, use the
macro define-generic-mode. See the file generic-x.el
for some examples of the use of define-generic-mode.
This macro defines a generic mode command named mode (a symbol, not quoted). The optional argument docstring is the documentation for the mode command. If you do not supply it,
define-generic-modegenerates one by default.The argument comment-list is a list in which each element is either a character, a string of one or two characters, or a cons cell. A character or a string is set up in the mode's syntax table as a comment starter. If the entry is a cons cell, the car is set up as a comment starter and the cdr as a comment ender. (Use
nilfor the latter if you want comments to end at the end of the line.) Note that the syntax table mechanism has limitations about what comment starters and enders are actually possible. See Syntax Tables.The argument keyword-list is a list of keywords to highlight with
font-lock-keyword-face. Each keyword should be a string. Meanwhile, font-lock-list is a list of additional expressions to highlight. Each element of this list should have the same form as an element offont-lock-keywords. See Search-based Fontification.The argument auto-mode-list is a list of regular expressions to add to the variable
auto-mode-alist. They are added by the execution of thedefine-generic-modeform, not by expanding the macro call.Finally, function-list is a list of functions for the mode command to call for additional setup. It calls these functions just before it runs the mode hook variable mode
-hook.
Text mode is perhaps the simplest mode besides Fundamental mode. Here are excerpts from text-mode.el that illustrate many of the conventions listed above:
;; Create the syntax table for this mode. (defvar text-mode-syntax-table (let ((st (make-syntax-table))) (modify-syntax-entry ?\" ". " st) (modify-syntax-entry ?\\ ". " st) ;; Add 'p' so M-c on 'hello' leads to 'Hello', not 'hello'. (modify-syntax-entry ?' "w p" st) st) "Syntax table used while in `text-mode'.") ;; Create the keymap for this mode. (defvar text-mode-map (let ((map (make-sparse-keymap))) (define-key map "\e\t" 'ispell-complete-word) map) "Keymap for `text-mode'. Many other modes, such as `mail-mode', `outline-mode' and `indented-text-mode', inherit all the commands defined in this map.")
Here is how the actual mode command is defined now:
(define-derived-mode text-mode nil "Text"
"Major mode for editing text written for humans to read.
In this mode, paragraphs are delimited only by blank or white lines.
You can thus get the full benefit of adaptive filling
(see the variable `adaptive-fill-mode').
\\{text-mode-map}
Turning on Text mode runs the normal hook `text-mode-hook'."
(set (make-local-variable 'text-mode-variant) t)
(set (make-local-variable 'require-final-newline)
mode-require-final-newline)
(set (make-local-variable 'indent-line-function) 'indent-relative))
(The last line is redundant nowadays, since indent-relative is
the default value, and we'll delete it in a future version.)
The three Lisp modes (Lisp mode, Emacs Lisp mode, and Lisp Interaction mode) have more features than Text mode and the code is correspondingly more complicated. Here are excerpts from lisp-mode.el that illustrate how these modes are written.
Here is how the Lisp mode syntax and abbrev tables are defined:
;; Create mode-specific table variables.
(defvar lisp-mode-abbrev-table nil)
(define-abbrev-table 'lisp-mode-abbrev-table ())
(defvar lisp-mode-syntax-table
(let ((table (copy-syntax-table emacs-lisp-mode-syntax-table)))
(modify-syntax-entry ?\[ "_ " table)
(modify-syntax-entry ?\] "_ " table)
(modify-syntax-entry ?# "' 14" table)
(modify-syntax-entry ?| "\" 23bn" table)
table)
"Syntax table used in `lisp-mode'.")
The three modes for Lisp share much of their code. For instance, each calls the following function to set various variables:
(defun lisp-mode-variables (&optional syntax keywords-case-insensitive)
(when syntax
(set-syntax-table lisp-mode-syntax-table))
(setq local-abbrev-table lisp-mode-abbrev-table)
...
Amongst other things, this function sets up the comment-start
variable to handle Lisp comments:
(make-local-variable 'comment-start)
(setq comment-start ";")
...
Each of the different Lisp modes has a slightly different keymap. For
example, Lisp mode binds C-c C-z to run-lisp, but the other
Lisp modes do not. However, all Lisp modes have some commands in
common. The following code sets up the common commands:
(defvar lisp-mode-shared-map
(let ((map (make-sparse-keymap)))
(define-key map "\e\C-q" 'indent-sexp)
(define-key map "\177" 'backward-delete-char-untabify)
map)
"Keymap for commands shared by all sorts of Lisp modes.")
And here is the code to set up the keymap for Lisp mode:
(defvar lisp-mode-map
(let ((map (make-sparse-keymap))
(menu-map (make-sparse-keymap "Lisp")))
(set-keymap-parent map lisp-mode-shared-map)
(define-key map "\e\C-x" 'lisp-eval-defun)
(define-key map "\C-c\C-z" 'run-lisp)
...
map)
"Keymap for ordinary Lisp mode.
All commands in `lisp-mode-shared-map' are inherited by this map.")
Finally, here is the major mode command for Lisp mode:
(define-derived-mode lisp-mode prog-mode "Lisp"
"Major mode for editing Lisp code for Lisps other than GNU Emacs Lisp.
Commands:
Delete converts tabs to spaces as it moves back.
Blank lines separate paragraphs. Semicolons start comments.
\\{lisp-mode-map}
Note that `run-lisp' may be used either to start an inferior Lisp job
or to switch back to an existing one.
Entry to this mode calls the value of `lisp-mode-hook'
if that value is non-nil."
(lisp-mode-variables nil t)
(set (make-local-variable 'find-tag-default-function)
'lisp-find-tag-default)
(set (make-local-variable 'comment-start-skip)
"\\(\\(^\\|[^\\\\\n]\\)\\(\\\\\\\\\\)*\\)\\(;+\\|#|\\) *")
(setq imenu-case-fold-search t))
A minor mode provides optional features that users may enable or disable independently of the choice of major mode. Minor modes can be enabled individually or in combination.
Most minor modes implement features that are independent of the major mode, and can thus be used with most major modes. For example, Auto Fill mode works with any major mode that permits text insertion. A few minor modes, however, are specific to a particular major mode. For example, Diff Auto Refine mode is a minor mode that is intended to be used only with Diff mode.
Ideally, a minor mode should have its desired effect regardless of the other minor modes in effect. It should be possible to activate and deactivate minor modes in any order.
There are conventions for writing minor modes just as there are for
major modes. These conventions are described below. The easiest way to
follow them is to use the macro define-minor-mode.
See Defining Minor Modes.
nil if the mode is disabled, and non-nil
if the mode is enabled. The variable should be buffer-local if the
minor mode is buffer-local.
This variable is used in conjunction with the minor-mode-alist to
display the minor mode name in the mode line. It also determines
whether the minor mode keymap is active, via minor-mode-map-alist
(see Controlling Active Maps). Individual commands or hooks can
also check its value.
The mode command should accept one optional argument. If called interactively with no prefix argument, it should toggle the mode (i.e., enable if it is disabled, and disable if it is enabled). If called interactively with a prefix argument, it should enable the mode if the argument is positive and disable it otherwise.
If the mode command is called from Lisp (i.e., non-interactively), it
should enable the mode if the argument is omitted or nil; it
should toggle the mode if the argument is the symbol toggle;
otherwise it should treat the argument in the same way as for an
interactive call with a numeric prefix argument, as described above.
The following example shows how to implement this behavior (it is
similar to the code generated by the define-minor-mode macro):
(interactive (list (or current-prefix-arg 'toggle)))
(let ((enable (if (eq arg 'toggle)
(not foo-mode) ; this mode's mode variable
(> (prefix-numeric-value arg) 0))))
(if enable
do-enable
do-disable))
The reason for this somewhat complex behavior is that it lets users easily toggle the minor mode interactively, and also lets the minor mode be easily enabled in a mode hook, like this:
(add-hook 'text-mode-hook 'foo-mode)
This behaves correctly whether or not foo-mode was already
enabled, since the foo-mode mode command unconditionally enables
the minor mode when it is called from Lisp with no argument. Disabling
a minor mode in a mode hook is a little uglier:
(add-hook 'text-mode-hook (lambda () (foo-mode -1)))
However, this is not very commonly done.
minor-mode-alist for each minor mode
(see Definition of minor-mode-alist), if you want to indicate the
minor mode in the mode line. This element should be a list of the
following form:
(mode-variable string)
Here mode-variable is the variable that controls enabling of the minor mode, and string is a short string, starting with a space, to represent the mode in the mode line. These strings must be short so that there is room for several of them at once.
When you add an element to minor-mode-alist, use assq to
check for an existing element, to avoid duplication. For example:
(unless (assq 'leif-mode minor-mode-alist)
(push '(leif-mode " Leif") minor-mode-alist))
or like this, using add-to-list (see List Variables):
(add-to-list 'minor-mode-alist '(leif-mode " Leif"))
In addition, several major mode conventions apply to minor modes as well: those regarding the names of global symbols, the use of a hook at the end of the initialization function, and the use of keymaps and other tables.
The minor mode should, if possible, support enabling and disabling via
Custom (see Customization). To do this, the mode variable should be
defined with defcustom, usually with :type 'boolean. If
just setting the variable is not sufficient to enable the mode, you
should also specify a :set method which enables the mode by
invoking the mode command. Note in the variable's documentation string
that setting the variable other than via Custom may not take effect.
Also, mark the definition with an autoload cookie (see autoload cookie), and specify a :require so that customizing the variable
will load the library that defines the mode. For example:
;;;###autoload
(defcustom msb-mode nil
"Toggle msb-mode.
Setting this variable directly does not take effect;
use either \\[customize] or the function `msb-mode'."
:set 'custom-set-minor-mode
:initialize 'custom-initialize-default
:version "20.4"
:type 'boolean
:group 'msb
:require 'msb)
Each minor mode can have its own keymap, which is active when the mode
is enabled. To set up a keymap for a minor mode, add an element to the
alist minor-mode-map-alist. See Definition of minor-mode-map-alist.
One use of minor mode keymaps is to modify the behavior of certain
self-inserting characters so that they do something else as well as
self-insert. (Another way to customize self-insert-command is
through post-self-insert-hook. Apart from this, the facilities
for customizing self-insert-command are limited to special cases,
designed for abbrevs and Auto Fill mode. Do not try substituting your
own definition of self-insert-command for the standard one. The
editor command loop handles this function specially.)
Minor modes may bind commands to key sequences consisting of C-c followed by a punctuation character. However, sequences consisting of C-c followed by one of {}<>:;, or a control character or digit, are reserved for major modes. Also, C-c letter is reserved for users. See Key Binding Conventions.
The macro define-minor-mode offers a convenient way of
implementing a mode in one self-contained definition.
This macro defines a new minor mode whose name is mode (a symbol). It defines a command named mode to toggle the minor mode, with doc as its documentation string.
The toggle command takes one optional (prefix) argument. If called interactively with no argument it toggles the mode on or off. A positive prefix argument enables the mode, any other prefix argument disables it. From Lisp, an argument of
toggletoggles the mode, whereas an omitted ornilargument enables the mode. This makes it easy to enable the minor mode in a major mode hook, for example. If doc isnil, the macro supplies a default documentation string explaining the above.By default, it also defines a variable named mode, which is set to
tornilby enabling or disabling the mode. The variable is initialized to init-value. Except in unusual circumstances (see below), this value must benil.The string lighter says what to display in the mode line when the mode is enabled; if it is
nil, the mode is not displayed in the mode line.The optional argument keymap specifies the keymap for the minor mode. If non-
nil, it should be a variable name (whose value is a keymap), a keymap, or an alist of the form(key-sequence . definition)where each key-sequence and definition are arguments suitable for passing to
define-key(see Changing Key Bindings). If keymap is a keymap or an alist, this also defines the variable mode-map.The above three arguments init-value, lighter, and keymap can be (partially) omitted when keyword-args are used. The keyword-args consist of keywords followed by corresponding values. A few keywords have special meanings:
:groupgroup- Custom group name to use in all generated
defcustomforms. Defaults to mode without the possible trailing `-mode'. Warning: don't use this default group name unless you have written adefgroupto define that group properly. See Group Definitions.
:globalglobal- If non-
nil, this specifies that the minor mode should be global rather than buffer-local. It defaults tonil.One of the effects of making a minor mode global is that the mode variable becomes a customization variable. Toggling it through the Customize interface turns the mode on and off, and its value can be saved for future Emacs sessions (see Saving Customizations. For the saved variable to work, you should ensure that the
define-minor-modeform is evaluated each time Emacs starts; for packages that are not part of Emacs, the easiest way to do this is to specify a:requirekeyword.:init-valueinit-value- This is equivalent to specifying init-value positionally.
:lighterlighter- This is equivalent to specifying lighter positionally.
:keymapkeymap- This is equivalent to specifying keymap positionally.
:variableplace- This replaces the default variable mode, used to store the state of the mode. If you specify this, the mode variable is not defined, and any init-value argument is unused. place can be a different named variable (which you must define yourself), or anything that can be used with the
setffunction (see Generalized Variables). place can also be a cons(get.set), where get is an expression that returns the current state, and set is a function of one argument (a state) that sets it.
:after-hookafter-hook- This defines a single Lisp form which is evaluated after the mode hooks have run. It should not be quoted.
Any other keyword arguments are passed directly to the
defcustomgenerated for the variable mode.The command named mode first performs the standard actions such as setting the variable named mode and then executes the body forms, if any. It then runs the mode hook variable mode
-hookand finishes by evaluating any form in:after-hook.
The initial value must be nil except in cases where (1) the
mode is preloaded in Emacs, or (2) it is painless for loading to
enable the mode even though the user did not request it. For
instance, if the mode has no effect unless something else is enabled,
and will always be loaded by that time, enabling it by default is
harmless. But these are unusual circumstances. Normally, the
initial value must be nil.
The name easy-mmode-define-minor-mode is an alias
for this macro.
Here is an example of using define-minor-mode:
(define-minor-mode hungry-mode
"Toggle Hungry mode.
Interactively with no argument, this command toggles the mode.
A positive prefix argument enables the mode, any other prefix
argument disables it. From Lisp, argument omitted or nil enables
the mode, `toggle' toggles the state.
When Hungry mode is enabled, the control delete key
gobbles all preceding whitespace except the last.
See the command \\[hungry-electric-delete]."
;; The initial value.
nil
;; The indicator for the mode line.
" Hungry"
;; The minor mode bindings.
'(([C-backspace] . hungry-electric-delete))
:group 'hunger)
This defines a minor mode named “Hungry mode”, a command named
hungry-mode to toggle it, a variable named hungry-mode
which indicates whether the mode is enabled, and a variable named
hungry-mode-map which holds the keymap that is active when the
mode is enabled. It initializes the keymap with a key binding for
C-<DEL>. It puts the variable hungry-mode into
custom group hunger. There are no body forms—many
minor modes don't need any.
Here's an equivalent way to write it:
(define-minor-mode hungry-mode
"Toggle Hungry mode.
...rest of documentation as before..."
;; The initial value.
:init-value nil
;; The indicator for the mode line.
:lighter " Hungry"
;; The minor mode bindings.
:keymap
'(([C-backspace] . hungry-electric-delete)
([C-M-backspace]
. (lambda ()
(interactive)
(hungry-electric-delete t))))
:group 'hunger)
This defines a global toggle named global-mode whose meaning is to enable or disable the buffer-local minor mode mode in all buffers. To turn on the minor mode in a buffer, it uses the function turn-on; to turn off the minor mode, it calls mode with −1 as argument.
Globally enabling the mode also affects buffers subsequently created by visiting files, and buffers that use a major mode other than Fundamental mode; but it does not detect the creation of a new buffer in Fundamental mode.
This defines the customization option global-mode (see Customization), which can be toggled in the Customize interface to turn the minor mode on and off. As with
define-minor-mode, you should ensure that thedefine-globalized-minor-modeform is evaluated each time Emacs starts, for example by providing a:requirekeyword.Use
:groupgroup in keyword-args to specify the custom group for the mode variable of the global minor mode.Generally speaking, when you define a globalized minor mode, you should also define a non-globalized version, so that people can use (or disable) it in individual buffers. This also allows them to disable a globally enabled minor mode in a specific major mode, by using that mode's hook.
Each Emacs window (aside from minibuffer windows) typically has a mode line at the bottom, which displays status information about the buffer displayed in the window. The mode line contains information about the buffer, such as its name, associated file, depth of recursive editing, and major and minor modes. A window can also have a header line, which is much like the mode line but appears at the top of the window.
This section describes how to control the contents of the mode line and header line. We include it in this chapter because much of the information displayed in the mode line relates to the enabled major and minor modes.
The contents of each mode line are specified by the buffer-local
variable mode-line-format (see Mode Line Top). This variable
holds a mode line construct: a template that controls what is
displayed on the buffer's mode line. The value of
header-line-format specifies the buffer's header line in the same
way. All windows for the same buffer use the same
mode-line-format and header-line-format.
For efficiency, Emacs does not continuously recompute each window's
mode line and header line. It does so when circumstances appear to call
for it—for instance, if you change the window configuration, switch
buffers, narrow or widen the buffer, scroll, or modify the buffer. If
you alter any of the variables referenced by mode-line-format or
header-line-format (see Mode Line Variables), or any other
data structures that affect how text is displayed (see Display), you
should use the function force-mode-line-update to update the
display.
This function forces Emacs to update the current buffer's mode line and header line, based on the latest values of all relevant variables, during its next redisplay cycle. If the optional argument all is non-
nil, it forces an update for all mode lines and header lines.This function also forces an update of the menu bar and frame title.
The selected window's mode line is usually displayed in a different
color using the face mode-line. Other windows' mode lines appear
in the face mode-line-inactive instead. See Faces.
The mode line contents are controlled by a data structure called a mode line construct, made up of lists, strings, symbols, and numbers kept in buffer-local variables. Each data type has a specific meaning for the mode line appearance, as described below. The same data structure is used for constructing frame titles (see Frame Titles) and header lines (see Header Lines).
A mode line construct may be as simple as a fixed string of text, but it usually specifies how to combine fixed strings with variables' values to construct the text. Many of these variables are themselves defined to have mode line constructs as their values.
Here are the meanings of various data types as mode line constructs:
%-constructs in it. These stand for substitution of
other data; see %-Constructs.
If parts of the string have face properties, they control
display of the text just as they would text in the buffer. Any
characters which have no face properties are displayed, by
default, in the face mode-line or mode-line-inactive
(see Standard Faces). The
help-echo and keymap properties in string have
special meanings. See Properties in Mode.
t and nil are ignored, as is any
symbol whose value is void.
There is one exception: if the value of symbol is a string, it is
displayed verbatim: the %-constructs are not recognized.
Unless symbol is marked as risky (i.e., it has a
non-nil risky-local-variable property), all text
properties specified in symbol's value are ignored. This includes
the text properties of strings in symbol's value, as well as all
:eval and :propertize forms in it. (The reason for this
is security: non-risky variables could be set automatically from file
variables without prompting the user.)
(string rest...)(list rest...)
(:eval form)
:eval says to evaluate
form, and use the result as a string to display. Make sure this
evaluation cannot load any files, as doing so could cause infinite
recursion.
(:propertize elt props...)
:propertize says to
process the mode line construct elt recursively, then add the text
properties specified by props to the result. The argument
props should consist of zero or more pairs text-property
value.
(symbol then else)
nil value, the second element,
then, is processed recursively as a mode line construct.
Otherwise, the third element, else, is processed recursively.
You may omit else; then the mode line construct displays nothing
if the value of symbol is nil or void.
(width rest...)
For example, the usual way to show what percentage of a buffer is above
the top of the window is to use a list like this: (-3 "%p").
The variable in overall control of the mode line is
mode-line-format.
The value of this variable is a mode line construct that controls the contents of the mode-line. It is always buffer-local in all buffers.
If you set this variable to
nilin a buffer, that buffer does not have a mode line. (A window that is just one line tall also does not display a mode line.)
The default value of mode-line-format is designed to use the
values of other variables such as mode-line-position and
mode-line-modes (which in turn incorporates the values of the
variables mode-name and minor-mode-alist). Very few
modes need to alter mode-line-format itself. For most
purposes, it is sufficient to alter some of the variables that
mode-line-format either directly or indirectly refers to.
If you do alter mode-line-format itself, the new value should
use the same variables that appear in the default value (see Mode Line Variables), rather than duplicating their contents or displaying
the information in another fashion. This way, customizations made by
the user or by Lisp programs (such as display-time and major
modes) via changes to those variables remain effective.
Here is a hypothetical example of a mode-line-format that might
be useful for Shell mode (in reality, Shell mode does not set
mode-line-format):
(setq mode-line-format
(list "-"
'mode-line-mule-info
'mode-line-modified
'mode-line-frame-identification
"%b--"
;; Note that this is evaluated while making the list.
;; It makes a mode line construct which is just a string.
(getenv "HOST")
":"
'default-directory
" "
'global-mode-string
" %[("
'(:eval (mode-line-mode-name))
'mode-line-process
'minor-mode-alist
"%n"
")%]--"
'(which-func-mode ("" which-func-format "--"))
'(line-number-mode "L%l--")
'(column-number-mode "C%c--")
'(-3 "%p")))
(The variables line-number-mode, column-number-mode
and which-func-mode enable particular minor modes; as usual,
these variable names are also the minor mode command names.)
This section describes variables incorporated by the standard value of
mode-line-format into the text of the mode line. There is
nothing inherently special about these variables; any other variables
could have the same effects on the mode line if the value of
mode-line-format is changed to use them. However, various parts
of Emacs set these variables on the understanding that they will control
parts of the mode line; therefore, practically speaking, it is essential
for the mode line to use them. Also see
Optional Mode Line.
This variable holds the value of the mode line construct that displays information about the language environment, buffer coding system, and current input method. See Non-ASCII Characters.
This variable holds the value of the mode line construct that displays whether the current buffer is modified. Its default value displays `**' if the buffer is modified, `--' if the buffer is not modified, `%%' if the buffer is read only, and `%*' if the buffer is read only and modified.
Changing this variable does not force an update of the mode line.
This variable identifies the current frame. Its default value displays
" "if you are using a window system which can show multiple frames, or"-%F "on an ordinary terminal which shows only one frame at a time.
This variable identifies the buffer being displayed in the window. Its default value displays the buffer name, padded with spaces to at least 12 columns.
This variable indicates the position in the buffer. Its default value displays the buffer percentage and, optionally, the buffer size, the line number and the column number.
The variable
vc-mode, buffer-local in each buffer, records whether the buffer's visited file is maintained with version control, and, if so, which kind. Its value is a string that appears in the mode line, ornilfor no version control.
This variable displays the buffer's major and minor modes. Its default value also displays the recursive editing level, information on the process status, and whether narrowing is in effect.
This variable is used to show whether
default-directoryfor the current buffer is remote.
The following three variables are used in mode-line-modes:
This buffer-local variable holds the “pretty” name of the current buffer's major mode. Each major mode should set this variable so that the mode name will appear in the mode line. The value does not have to be a string, but can use any of the data types valid in a mode-line construct (see Mode Line Data). To compute the string that will identify the mode name in the mode line, use
format-mode-line(see Emulating Mode Line).
This buffer-local variable contains the mode line information on process status in modes used for communicating with subprocesses. It is displayed immediately following the major mode name, with no intervening space. For example, its value in the *shell* buffer is
(":%s"), which allows the shell to display its status along with the major mode as: `(Shell:run)'. Normally this variable isnil.
This variable is displayed at the front of the mode line. By default, this construct is displayed right at the beginning of the mode line, except that if there is a memory-full message, it is displayed first.
Mode line construct for miscellaneous information. By default, this shows the information specified by
global-mode-string.
This variable holds an association list whose elements specify how the mode line should indicate that a minor mode is active. Each element of the
minor-mode-alistshould be a two-element list:(minor-mode-variable mode-line-string)More generally, mode-line-string can be any mode line construct. It appears in the mode line when the value of minor-mode-variable is non-
nil, and not otherwise. These strings should begin with spaces so that they don't run together. Conventionally, the minor-mode-variable for a specific mode is set to a non-nilvalue when that minor mode is activated.
minor-mode-alistitself is not buffer-local. Each variable mentioned in the alist should be buffer-local if its minor mode can be enabled separately in each buffer.
This variable holds a mode line construct that, by default, appears in the mode line just after the
which-func-modeminor mode if set, else aftermode-line-modes. The commanddisplay-timesetsglobal-mode-stringto refer to the variabledisplay-time-string, which holds a string containing the time and load information.The `%M' construct substitutes the value of
global-mode-string, but that is obsolete, since the variable is included in the mode line frommode-line-format.
Here is a simplified version of the default value of
mode-line-format. The real default value also
specifies addition of text properties.
("-"
mode-line-mule-info
mode-line-modified
mode-line-frame-identification
mode-line-buffer-identification
" "
mode-line-position
(vc-mode vc-mode)
" "
mode-line-modes
(which-func-mode ("" which-func-format "--"))
(global-mode-string ("--" global-mode-string))
"-%-")
%-Constructs in the Mode LineStrings used as mode line constructs can use certain
%-constructs to substitute various kinds of data. The
following is a list of the defined %-constructs, and what they
mean.
In any construct except `%%', you can add a decimal integer after the `%' to specify a minimum field width. If the width is less, the field is padded to that width. Purely numeric constructs (`c', `i', `I', and `l') are padded by inserting spaces to the left, and others are padded by inserting spaces to the right.
%bbuffer-name function.
See Buffer Names.
%c%e%fbuffer-file-name
function. See Buffer File Name.
%F%i(- (point-max) (point-min)).
%I%l%nnarrow-to-region in Narrowing).
%p%P%sprocess-status. See Process Information.
%z%Z%*buffer-read-only); buffer-modified-p); %+buffer-modified-p); buffer-read-only); %&%[%]%-%%%-constructs are allowed.
The following two %-constructs are still supported, but they are
obsolete, since you can get the same results with the variables
mode-name and global-mode-string.
%mmode-name.
%Mglobal-mode-string.
Certain text properties are meaningful in the
mode line. The face property affects the appearance of text; the
help-echo property associates help strings with the text, and
keymap can make the text mouse-sensitive.
There are four ways to specify text properties for text in the mode line:
(:propertize elt props...) construct to
give elt a text property specified by props.
:eval form in the mode line data
structure, and make form evaluate to a string that has a text
property.
You can use the keymap property to specify a keymap. This
keymap only takes real effect for mouse clicks; binding character keys
and function keys to it has no effect, since it is impossible to move
point into the mode line.
When the mode line refers to a variable which does not have a
non-nil risky-local-variable property, any text
properties given or specified within that variable's values are
ignored. This is because such properties could otherwise specify
functions to be called, and those functions could come from file
local variables.
A window can have a header line at the top, just as it can have
a mode line at the bottom. The header line feature works just like the
mode line feature, except that it's controlled by
header-line-format:
This variable, local in every buffer, specifies how to display the header line, for windows displaying the buffer. The format of the value is the same as for
mode-line-format(see Mode Line Data). It is normallynil, so that ordinary buffers have no header line.
This function returns the height in pixels of window's header line. window must be a live window, and defaults to the selected window.
A window that is just one line tall never displays a header line. A window that is two lines tall cannot display both a mode line and a header line at once; if it has a mode line, then it does not display a header line.
You can use the function format-mode-line to compute the text
that would appear in a mode line or header line based on a certain
mode line construct.
This function formats a line of text according to format as if it were generating the mode line for window, but it also returns the text as a string. The argument window defaults to the selected window. If buffer is non-
nil, all the information used is taken from buffer; by default, it comes from window's buffer.The value string normally has text properties that correspond to the faces, keymaps, etc., that the mode line would have. Any character for which no
faceproperty is specified by format gets a default value determined by face. If face ist, that stands for eithermode-lineif window is selected, otherwisemode-line-inactive. If face isnilor omitted, that stands for the default face. If face is an integer, the value returned by this function will have no text properties.You can also specify other valid faces as the value of face. If specified, that face provides the
faceproperty for characters whose face is not specified by format.Note that using
mode-line,mode-line-inactive, orheader-lineas face will actually redisplay the mode line or the header line, respectively, using the current definitions of the corresponding face, in addition to returning the formatted string. (Other faces do not cause redisplay.)For example,
(format-mode-line header-line-format)returns the text that would appear in the selected window's header line (""if it has no header line).(format-mode-line header-line-format 'header-line)returns the same text, with each character carrying the face that it will have in the header line itself, and also redraws the header line.
Imenu is a feature that lets users select a definition or
section in the buffer, from a menu which lists all of them, to go
directly to that location in the buffer. Imenu works by constructing
a buffer index which lists the names and buffer positions of the
definitions, or other named portions of the buffer; then the user can
choose one of them and move point to it. Major modes can add a menu
bar item to use Imenu using imenu-add-to-menubar.
This function defines a local menu bar item named name to run Imenu.
The user-level commands for using Imenu are described in the Emacs Manual (see Imenu). This section explains how to customize Imenu's method of finding definitions or buffer portions for a particular major mode.
The usual and simplest way is to set the variable
imenu-generic-expression:
This variable, if non-
nil, is a list that specifies regular expressions for finding definitions for Imenu. Simple elements ofimenu-generic-expressionlook like this:(menu-title regexp index)Here, if menu-title is non-
nil, it says that the matches for this element should go in a submenu of the buffer index; menu-title itself specifies the name for the submenu. If menu-title isnil, the matches for this element go directly in the top level of the buffer index.The second item in the list, regexp, is a regular expression (see Regular Expressions); anything in the buffer that it matches is considered a definition, something to mention in the buffer index. The third item, index, is a non-negative integer that indicates which subexpression in regexp matches the definition's name.
An element can also look like this:
(menu-title regexp index function arguments...)Each match for this element creates an index item, and when the index item is selected by the user, it calls function with arguments consisting of the item name, the buffer position, and arguments.
For Emacs Lisp mode,
imenu-generic-expressioncould look like this:((nil "^\\s-*(def\\(un\\|subst\\|macro\\|advice\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Vars*" "^\\s-*(def\\(var\\|const\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2) ("*Types*" "^\\s-*\ (def\\(type\\|struct\\|class\\|ine-condition\\)\ \\s-+\\([-A-Za-z0-9+]+\\)" 2))Setting this variable makes it buffer-local in the current buffer.
This variable controls whether matching against the regular expressions in the value of
imenu-generic-expressionis case-sensitive:t, the default, means matching should ignore case.Setting this variable makes it buffer-local in the current buffer.
This variable is an alist of syntax table modifiers to use while processing
imenu-generic-expression, to override the syntax table of the current buffer. Each element should have this form:(characters . syntax-description)The car, characters, can be either a character or a string. The element says to give that character or characters the syntax specified by syntax-description, which is passed to
modify-syntax-entry(see Syntax Table Functions).This feature is typically used to give word syntax to characters which normally have symbol syntax, and thus to simplify
imenu-generic-expressionand speed up matching. For example, Fortran mode uses it this way:(setq imenu-syntax-alist '(("_$" . "w")))The
imenu-generic-expressionregular expressions can then use `\\sw+' instead of `\\(\\sw\\|\\s_\\)+'. Note that this technique may be inconvenient when the mode needs to limit the initial character of a name to a smaller set of characters than are allowed in the rest of a name.Setting this variable makes it buffer-local in the current buffer.
Another way to customize Imenu for a major mode is to set the
variables imenu-prev-index-position-function and
imenu-extract-index-name-function:
If this variable is non-
nil, its value should be a function that finds the next definition to put in the buffer index, scanning backward in the buffer from point. It should returnnilif it doesn't find another definition before point. Otherwise it should leave point at the place it finds a definition and return any non-nilvalue.Setting this variable makes it buffer-local in the current buffer.
If this variable is non-
nil, its value should be a function to return the name for a definition, assuming point is in that definition as theimenu-prev-index-position-functionfunction would leave it.Setting this variable makes it buffer-local in the current buffer.
The last way to customize Imenu for a major mode is to set the
variable imenu-create-index-function:
This variable specifies the function to use for creating a buffer index. The function should take no arguments, and return an index alist for the current buffer. It is called within
save-excursion, so where it leaves point makes no difference.The index alist can have three types of elements. Simple elements look like this:
(index-name . index-position)Selecting a simple element has the effect of moving to position index-position in the buffer. Special elements look like this:
(index-name index-position function arguments...)Selecting a special element performs:
(funcall function index-name index-position arguments...)A nested sub-alist element looks like this:
(menu-title . sub-alist)It creates the submenu menu-title specified by sub-alist.
The default value of
imenu-create-index-functionisimenu-default-create-index-function. This function calls the value ofimenu-prev-index-position-functionand the value ofimenu-extract-index-name-functionto produce the index alist. However, if either of these two variables isnil, the default function usesimenu-generic-expressioninstead.Setting this variable makes it buffer-local in the current buffer.
Font Lock mode is a buffer-local minor mode that automatically
attaches face properties to certain parts of the buffer based on
their syntactic role. How it parses the buffer depends on the major
mode; most major modes define syntactic criteria for which faces to use
in which contexts. This section explains how to customize Font Lock for
a particular major mode.
Font Lock mode finds text to highlight in two ways: through syntactic parsing based on the syntax table, and through searching (usually for regular expressions). Syntactic fontification happens first; it finds comments and string constants and highlights them. Search-based fontification happens second.
The Font Lock functionality is based on several basic functions. Each of these calls the function specified by the corresponding variable. This indirection allows major and minor modes to modify the way fontification works in the buffers of that mode, and even use the Font Lock mechanisms for features that have nothing to do with fontification. (This is why the description below says “should” when it describes what the functions do: the mode can customize the values of the corresponding variables to do something entirely different.) The variables mentioned below are described in Other Font Lock Variables.
font-lock-fontify-buffer
font-lock-fontify-buffer-function.
font-lock-unfontify-buffer
font-lock-unfontify-buffer-function.
font-lock-fontify-region beg end &optional loudly
nil, should display status messages while
fontifying. Calls the function specified by
font-lock-fontify-region-function.
font-lock-unfontify-region beg end
font-lock-unfontify-region-function.
font-lock-flush &optional beg end
nil,
beg and end default to the beginning and end of the
buffer's accessible portion. Calls the function specified by
font-lock-flush-function.
font-lock-ensure &optional beg end
font-lock-ensure-function.
There are several variables that control how Font Lock mode highlights
text. But major modes should not set any of these variables directly.
Instead, they should set font-lock-defaults as a buffer-local
variable. The value assigned to this variable is used, if and when Font
Lock mode is enabled, to set all the other variables.
This variable is set by modes to specify how to fontify text in that mode. It automatically becomes buffer-local when set. If its value is
nil, Font Lock mode does no highlighting, and you can use the `Faces' menu (under `Edit' and then `Text Properties' in the menu bar) to assign faces explicitly to text in the buffer.If non-
nil, the value should look like this:(keywords [keywords-only [case-fold [syntax-alist other-vars...]]])The first element, keywords, indirectly specifies the value of
font-lock-keywordswhich directs search-based fontification. It can be a symbol, a variable or a function whose value is the list to use forfont-lock-keywords. It can also be a list of several such symbols, one for each possible level of fontification. The first symbol specifies the `mode default' level of fontification, the next symbol level 1 fontification, the next level 2, and so on. The `mode default' level is normally the same as level 1. It is used whenfont-lock-maximum-decorationhas anilvalue. See Levels of Font Lock.The second element, keywords-only, specifies the value of the variable
font-lock-keywords-only. If this is omitted ornil, syntactic fontification (of strings and comments) is also performed. If this is non-nil, syntactic fontification is not performed. See Syntactic Font Lock.The third element, case-fold, specifies the value of
font-lock-keywords-case-fold-search. If it is non-nil, Font Lock mode ignores case during search-based fontification.If the fourth element, syntax-alist, is non-
nil, it should be a list of cons cells of the form(char-or-string.string). These are used to set up a syntax table for syntactic fontification; the resulting syntax table is stored infont-lock-syntax-table. If syntax-alist is omitted ornil, syntactic fontification uses the syntax table returned by thesyntax-tablefunction. See Syntax Table Functions.All the remaining elements (if any) are collectively called other-vars. Each of these elements should have the form
(variable.value)—which means, make variable buffer-local and then set it to value. You can use these other-vars to set other variables that affect fontification, aside from those you can control with the first five elements. See Other Font Lock Variables.
If your mode fontifies text explicitly by adding
font-lock-face properties, it can specify (nil t) for
font-lock-defaults to turn off all automatic fontification.
However, this is not required; it is possible to fontify some things
using font-lock-face properties and set up automatic
fontification for other parts of the text.
The variable which directly controls search-based fontification is
font-lock-keywords, which is typically specified via the
keywords element in font-lock-defaults.
The value of this variable is a list of the keywords to highlight. Lisp programs should not set this variable directly. Normally, the value is automatically set by Font Lock mode, using the keywords element in
font-lock-defaults. The value can also be altered using the functionsfont-lock-add-keywordsandfont-lock-remove-keywords(see Customizing Keywords).
Each element of font-lock-keywords specifies how to find
certain cases of text, and how to highlight those cases. Font Lock mode
processes the elements of font-lock-keywords one by one, and for
each element, it finds and handles all matches. Ordinarily, once
part of the text has been fontified already, this cannot be overridden
by a subsequent match in the same text; but you can specify different
behavior using the override element of a subexp-highlighter.
Each element of font-lock-keywords should have one of these
forms:
font-lock-keyword-face. For example,
;; Highlight occurrences of the word `foo'
;; using font-lock-keyword-face.
"\\<foo\\>"
Be careful when composing these regular expressions; a poorly written
pattern can dramatically slow things down! The function
regexp-opt (see Regexp Functions) is useful for calculating
optimal regular expressions to match several keywords.
font-lock-keyword-face.
When function is called, it receives one argument, the limit of
the search; it should begin searching at point, and not search beyond the
limit. It should return non-nil if it succeeds, and set the
match data to describe the match that was found. Returning nil
indicates failure of the search.
Fontification will call function repeatedly with the same limit,
and with point where the previous invocation left it, until
function fails. On failure, function need not reset point
in any particular way.
(matcher . subexp)
;; Highlight the `bar' in each occurrence of `fubar',
;; using font-lock-keyword-face.
("fu\\(bar\\)" . 1)
If you use regexp-opt to produce the regular expression
matcher, you can use regexp-opt-depth (see Regexp Functions) to calculate the value for subexp.
(matcher . facespec)
;; Highlight occurrences of `fubar',
;; using the face which is the value of fubar-face.
("fubar" . fubar-face)
However, facespec can also evaluate to a list of this form:
(face face prop1 val1 prop2 val2...)
to specify the face face and various additional text properties
to put on the text that matches. If you do this, be sure to add the
other text property names that you set in this way to the value of
font-lock-extra-managed-props so that the properties will also
be cleared out when they are no longer appropriate. Alternatively,
you can set the variable font-lock-unfontify-region-function to
a function that clears these properties. See Other Font Lock Variables.
(matcher . subexp-highlighter)
(subexp facespec [override [laxmatch]])
The car, subexp, is an integer specifying which subexpression of the match to fontify (0 means the entire matching text). The second subelement, facespec, is an expression whose value specifies the face, as described above.
The last two values in subexp-highlighter, override and
laxmatch, are optional flags. If override is t,
this element can override existing fontification made by previous
elements of font-lock-keywords. If it is keep, then
each character is fontified if it has not been fontified already by
some other element. If it is prepend, the face specified by
facespec is added to the beginning of the font-lock-face
property. If it is append, the face is added to the end of the
font-lock-face property.
If laxmatch is non-nil, it means there should be no error
if there is no subexpression numbered subexp in matcher.
Obviously, fontification of the subexpression numbered subexp will
not occur. However, fontification of other subexpressions (and other
regexps) will continue. If laxmatch is nil, and the
specified subexpression is missing, then an error is signaled which
terminates search-based fontification.
Here are some examples of elements of this kind, and what they do:
;; Highlight occurrences of either `foo' or `bar', using ;;foo-bar-face, even if they have already been highlighted. ;;foo-bar-faceshould be a variable whose value is a face. ("foo\\|bar" 0 foo-bar-face t) ;; Highlight the first subexpression within each occurrence ;; that the functionfubar-matchfinds, ;; using the face which is the value offubar-face. (fubar-match 1 fubar-face)
(matcher . anchored-highlighter)
(anchored-matcher pre-form post-form
subexp-highlighters...)
Here, anchored-matcher, like matcher, is either a regular expression or a function. After a match of matcher is found, point is at the end of the match. Now, Font Lock evaluates the form pre-form. Then it searches for matches of anchored-matcher and uses subexp-highlighters to highlight these. A subexp-highlighter is as described above. Finally, Font Lock evaluates post-form.
The forms pre-form and post-form can be used to initialize before, and cleanup after, anchored-matcher is used. Typically, pre-form is used to move point to some position relative to the match of matcher, before starting with anchored-matcher. post-form might be used to move back, before resuming with matcher.
After Font Lock evaluates pre-form, it does not search for anchored-matcher beyond the end of the line. However, if pre-form returns a buffer position that is greater than the position of point after pre-form is evaluated, then the position returned by pre-form is used as the limit of the search instead. It is generally a bad idea to return a position greater than the end of the line; in other words, the anchored-matcher search should not span lines.
For example,
;; Highlight occurrences of the word `item' following
;; an occurrence of the word `anchor' (on the same line)
;; in the value of item-face.
("\\<anchor\\>" "\\<item\\>" nil nil (0 item-face))
Here, pre-form and post-form are nil. Therefore
searching for `item' starts at the end of the match of
`anchor', and searching for subsequent instances of `anchor'
resumes from where searching for `item' concluded.
(matcher highlighters...)
For example,
;; Highlight occurrences of the word `anchor' in the value ;; ofanchor-face, and subsequent occurrences of the word ;; `item' (on the same line) in the value ofitem-face. ("\\<anchor\\>" (0 anchor-face) ("\\<item\\>" nil nil (0 item-face)))
(eval . form)
font-lock-keywords is used in a buffer.
Its value should have one of the forms described in this table.
Warning: Do not design an element of font-lock-keywords
to match text which spans lines; this does not work reliably.
For details, see See Multiline Font Lock.
You can use case-fold in font-lock-defaults to specify
the value of font-lock-keywords-case-fold-search which says
whether search-based fontification should be case-insensitive.
Non-
nilmeans that regular expression matching for the sake offont-lock-keywordsshould be case-insensitive.
You can use font-lock-add-keywords to add additional
search-based fontification rules to a major mode, and
font-lock-remove-keywords to remove rules.
This function adds highlighting keywords, for the current buffer or for major mode mode. The argument keywords should be a list with the same format as the variable
font-lock-keywords.If mode is a symbol which is a major mode command name, such as
c-mode, the effect is that enabling Font Lock mode in mode will add keywords tofont-lock-keywords. Calling with a non-nilvalue of mode is correct only in your ~/.emacs file.If mode is
nil, this function adds keywords tofont-lock-keywordsin the current buffer. This way of callingfont-lock-add-keywordsis usually used in mode hook functions.By default, keywords are added at the beginning of
font-lock-keywords. If the optional argument how isset, they are used to replace the value offont-lock-keywords. If how is any other non-nilvalue, they are added at the end offont-lock-keywords.Some modes provide specialized support you can use in additional highlighting patterns. See the variables
c-font-lock-extra-types,c++-font-lock-extra-types, andjava-font-lock-extra-types, for example.Warning: Major mode commands must not call
font-lock-add-keywordsunder any circumstances, either directly or indirectly, except through their mode hooks. (Doing so would lead to incorrect behavior for some minor modes.) They should set up their rules for search-based fontification by settingfont-lock-keywords.
This function removes keywords from
font-lock-keywordsfor the current buffer or for major mode mode. As infont-lock-add-keywords, mode should be a major mode command name ornil. All the caveats and requirements forfont-lock-add-keywordsapply here too.
For example, the following code adds two fontification patterns for C mode: one to fontify the word `FIXME', even in comments, and another to fontify the words `and', `or' and `not' as keywords.
(font-lock-add-keywords 'c-mode
'(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
("\\<\\(and\\|or\\|not\\)\\>" . font-lock-keyword-face)))
This example affects only C mode proper. To add the same patterns to C mode and all modes derived from it, do this instead:
(add-hook 'c-mode-hook
(lambda ()
(font-lock-add-keywords nil
'(("\\<\\(FIXME\\):" 1 font-lock-warning-face prepend)
("\\<\\(and\\|or\\|not\\)\\>" .
font-lock-keyword-face)))))
This section describes additional variables that a major mode can
set by means of other-vars in font-lock-defaults
(see Font Lock Basics).
If this variable is non-
nil, it should be a function that is called with no arguments, to choose an enclosing range of text for refontification for the command M-o M-o (font-lock-fontify-block).The function should report its choice by placing the region around it. A good choice is a range of text large enough to give proper results, but not too large so that refontification becomes slow. Typical values are
mark-defunfor programming modes ormark-paragraphfor textual modes.
This variable specifies additional properties (other than
font-lock-face) that are being managed by Font Lock mode. It is used byfont-lock-default-unfontify-region, which normally only manages thefont-lock-faceproperty. If you want Font Lock to manage other properties as well, you must specify them in a facespec infont-lock-keywordsas well as add them to this list. See Search-based Fontification.
Function to use for fontifying the buffer. The default value is
font-lock-default-fontify-buffer.
Function to use for unfontifying the buffer. This is used when turning off Font Lock mode. The default value is
font-lock-default-unfontify-buffer.
Function to use for fontifying a region. It should take two arguments, the beginning and end of the region, and an optional third argument verbose. If verbose is non-
nil, the function should print status messages. The default value isfont-lock-default-fontify-region.
Function to use for unfontifying a region. It should take two arguments, the beginning and end of the region. The default value is
font-lock-default-unfontify-region.
Function to use for declaring that a region's fontification is out of date. It takes two arguments, the beginning and end of the region. The default value of this variable is
font-lock-after-change-function.
Function to use for making sure a region of the current buffer has been fontified. It is called with two arguments, the beginning and end of the region. The default value of this variable is a function that calls
font-lock-default-fontify-bufferif the buffer is not fontified; the effect is to make sure the entire accessible portion of the buffer is fontified.
This function tells Font Lock mode to run the Lisp function function any time it has to fontify or refontify part of the current buffer. It calls function before calling the default fontification functions, and gives it two arguments, start and end, which specify the region to be fontified or refontified.
The optional argument contextual, if non-
nil, forces Font Lock mode to always refontify a syntactically relevant part of the buffer, and not just the modified lines. This argument can usually be omitted.
If function was previously registered as a fontification function using
jit-lock-register, this function unregisters it.
Some major modes offer three different levels of fontification. You
can define multiple levels by using a list of symbols for keywords
in font-lock-defaults. Each symbol specifies one level of
fontification; it is up to the user to choose one of these levels,
normally by setting font-lock-maximum-decoration (see Font Lock). The chosen level's symbol value
is used to initialize font-lock-keywords.
Here are the conventions for how to define the levels of fontification:
Some major modes such as list-buffers and occur
construct the buffer text programmatically. The easiest way for them
to support Font Lock mode is to specify the faces of text when they
insert the text in the buffer.
The way to do this is to specify the faces in the text with the
special text property font-lock-face (see Special Properties). When Font Lock mode is enabled, this property controls
the display, just like the face property. When Font Lock mode
is disabled, font-lock-face has no effect on the display.
It is ok for a mode to use font-lock-face for some text and
also use the normal Font Lock machinery. But if the mode does not use
the normal Font Lock machinery, it should not set the variable
font-lock-defaults.
Font Lock mode can highlight using any face, but Emacs defines several faces specifically for Font Lock to use to highlight text. These Font Lock faces are listed below. They can also be used by major modes for syntactic highlighting outside of Font Lock mode (see Major Mode Conventions).
Each of these symbols is both a face name, and a variable whose
default value is the symbol itself. Thus, the default value of
font-lock-comment-face is font-lock-comment-face.
The faces are listed with descriptions of their typical usage, and in order of greater to lesser prominence. If a mode's syntactic categories do not fit well with the usage descriptions, the faces can be assigned using the ordering as a guide.
font-lock-warning-facefont-lock-function-name-facefont-lock-variable-name-facefont-lock-keyword-facefont-lock-comment-facefont-lock-comment-delimiter-facefont-lock-comment-face.
font-lock-type-facefont-lock-constant-facefont-lock-builtin-facefont-lock-preprocessor-facefont-lock-builtin-face.
font-lock-string-facefont-lock-doc-facefont-lock-string-face.
font-lock-negation-char-face
Syntactic fontification uses a syntax table (see Syntax Tables) to
find and highlight syntactically relevant text. If enabled, it runs
prior to search-based fontification. The variable
font-lock-syntactic-face-function, documented below, determines
which syntactic constructs to highlight. There are several variables
that affect syntactic fontification; you should set them by means of
font-lock-defaults (see Font Lock Basics).
Whenever Font Lock mode performs syntactic fontification on a stretch
of text, it first calls the function specified by
syntax-propertize-function. Major modes can use this to apply
syntax-table text properties to override the buffer's syntax
table in special cases. See Syntax Properties.
If the value of this variable is non-
nil, Font Lock does not do syntactic fontification, only search-based fontification based onfont-lock-keywords. It is normally set by Font Lock mode based on the keywords-only element infont-lock-defaults.
This variable holds the syntax table to use for fontification of comments and strings. It is normally set by Font Lock mode based on the syntax-alist element in
font-lock-defaults. If this value isnil, syntactic fontification uses the buffer's syntax table (the value returned by the functionsyntax-table; see Syntax Table Functions).
If this variable is non-
nil, it should be a function to determine which face to use for a given syntactic element (a string or a comment). The value is normally set through an other-vars element infont-lock-defaults.The function is called with one argument, the parse state at point returned by
parse-partial-sexp, and should return a face. The default value returnsfont-lock-comment-facefor comments andfont-lock-string-facefor strings (see Faces for Font Lock).
Normally, elements of font-lock-keywords should not match
across multiple lines; that doesn't work reliably, because Font Lock
usually scans just part of the buffer, and it can miss a multi-line
construct that crosses the line boundary where the scan starts. (The
scan normally starts at the beginning of a line.)
Making elements that match multiline constructs work properly has two aspects: correct identification and correct rehighlighting. The first means that Font Lock finds all multiline constructs. The second means that Font Lock will correctly rehighlight all the relevant text when a multiline construct is changed—for example, if some of the text that was previously part of a multiline construct ceases to be part of it. The two aspects are closely related, and often getting one of them to work will appear to make the other also work. However, for reliable results you must attend explicitly to both aspects.
There are three ways to ensure correct identification of multiline constructs:
font-lock-extend-region-functions that does
the identification and extends the scan so that the scanned
text never starts or ends in the middle of a multiline construct.
font-lock-fontify-region-function hook similarly to
extend the scan so that the scanned text never starts or ends in the
middle of a multiline construct.
font-lock-multiline
which will instruct font-lock not to start or end the scan in the
middle of the construct.
There are three ways to do rehighlighting of multiline constructs:
font-lock-multiline property on the construct. This
will rehighlight the whole construct if any part of it is changed. In
some cases you can do this automatically by setting the
font-lock-multiline variable, which see.
jit-lock-contextually is set and rely on it doing its
job. This will only rehighlight the part of the construct that
follows the actual change, and will do it after a short delay.
This only works if the highlighting of the various parts of your
multiline construct never depends on text in subsequent lines.
Since jit-lock-contextually is activated by default, this can
be an attractive solution.
jit-lock-defer-multiline property on the construct.
This works only if jit-lock-contextually is used, and with the
same delay before rehighlighting, but like font-lock-multiline,
it also handles the case where highlighting depends on
subsequent lines.
One way to ensure reliable rehighlighting of multiline Font Lock
constructs is to put on them the text property font-lock-multiline.
It should be present and non-nil for text that is part of a
multiline construct.
When Font Lock is about to highlight a range of text, it first
extends the boundaries of the range as necessary so that they do not
fall within text marked with the font-lock-multiline property.
Then it removes any font-lock-multiline properties from the
range, and highlights it. The highlighting specification (mostly
font-lock-keywords) must reinstall this property each time,
whenever it is appropriate.
Warning: don't use the font-lock-multiline property
on large ranges of text, because that will make rehighlighting slow.
If the
font-lock-multilinevariable is set tot, Font Lock will try to add thefont-lock-multilineproperty automatically on multiline constructs. This is not a universal solution, however, since it slows down Font Lock somewhat. It can miss some multiline constructs, or make the property larger or smaller than necessary.For elements whose matcher is a function, the function should ensure that submatch 0 covers the whole relevant multiline construct, even if only a small subpart will be highlighted. It is often just as easy to add the
font-lock-multilineproperty by hand.
The font-lock-multiline property is meant to ensure proper
refontification; it does not automatically identify new multiline
constructs. Identifying the requires that Font Lock mode operate on
large enough chunks at a time. This will happen by accident on many
cases, which may give the impression that multiline constructs magically
work. If you set the font-lock-multiline variable
non-nil, this impression will be even stronger, since the
highlighting of those constructs which are found will be properly
updated from then on. But that does not work reliably.
To find multiline constructs reliably, you must either manually place
the font-lock-multiline property on the text before Font Lock
mode looks at it, or use font-lock-fontify-region-function.
When a buffer is changed, the region that Font Lock refontifies is by default the smallest sequence of whole lines that spans the change. While this works well most of the time, sometimes it doesn't—for example, when a change alters the syntactic meaning of text on an earlier line.
You can enlarge (or even reduce) the region to refontify by setting the following variable:
This buffer-local variable is either
nilor a function for Font Lock mode to call to determine the region to scan and fontify.The function is given three parameters, the standard beg, end, and old-len from
after-change-functions(see Change Hooks). It should return either a cons of the beginning and end buffer positions (in that order) of the region to fontify, ornil(which means choose the region in the standard way). This function needs to preserve point, the match-data, and the current restriction. The region it returns may start or end in the middle of a line.Since this function is called after every buffer change, it should be reasonably fast.
For programming languages, an important feature of a major mode is to
provide automatic indentation. There are two parts: one is to decide what
is the right indentation of a line, and the other is to decide when to
reindent a line. By default, Emacs reindents a line whenever you
type a character in electric-indent-chars, which by default only
includes Newline. Major modes can add chars to electric-indent-chars
according to the syntax of the language.
Deciding what is the right indentation is controlled in Emacs by
indent-line-function (see Mode-Specific Indent). For some modes,
the right indentation cannot be known reliably, typically because
indentation is significant so several indentations are valid but with different
meanings. In that case, the mode should set electric-indent-inhibit to
make sure the line is not constantly re-indented against the user's wishes.
Writing a good indentation function can be difficult and to a large extent it is still a black art. Many major mode authors will start by writing a simple indentation function that works for simple cases, for example by comparing with the indentation of the previous text line. For most programming languages that are not really line-based, this tends to scale very poorly: improving such a function to let it handle more diverse situations tends to become more and more difficult, resulting in the end with a large, complex, unmaintainable indentation function which nobody dares to touch.
A good indentation function will usually need to actually parse the text, according to the syntax of the language. Luckily, it is not necessary to parse the text in as much detail as would be needed for a compiler, but on the other hand, the parser embedded in the indentation code will want to be somewhat friendly to syntactically incorrect code.
Good maintainable indentation functions usually fall into two categories: either parsing forward from some safe starting point until the position of interest, or parsing backward from the position of interest. Neither of the two is a clearly better choice than the other: parsing backward is often more difficult than parsing forward because programming languages are designed to be parsed forward, but for the purpose of indentation it has the advantage of not needing to guess a safe starting point, and it generally enjoys the property that only a minimum of text will be analyzed to decide the indentation of a line, so indentation will tend to be less affected by syntax errors in some earlier unrelated piece of code. Parsing forward on the other hand is usually easier and has the advantage of making it possible to reindent efficiently a whole region at a time, with a single parse.
Rather than write your own indentation function from scratch, it is often preferable to try and reuse some existing ones or to rely on a generic indentation engine. There are sadly few such engines. The CC-mode indentation code (used with C, C++, Java, Awk and a few other such modes) has been made more generic over the years, so if your language seems somewhat similar to one of those languages, you might try to use that engine. Another one is SMIE which takes an approach in the spirit of Lisp sexps and adapts it to non-Lisp languages.
SMIE is a package that provides a generic navigation and indentation engine. Based on a very simple parser using an operator precedence grammar, it lets major modes extend the sexp-based navigation of Lisp to non-Lisp languages as well as provide a simple to use but reliable auto-indentation.
Operator precedence grammar is a very primitive technology for parsing
compared to some of the more common techniques used in compilers.
It has the following characteristics: its parsing power is very limited,
and it is largely unable to detect syntax errors, but it has the
advantage of being algorithmically efficient and able to parse forward
just as well as backward. In practice that means that SMIE can use it
for indentation based on backward parsing, that it can provide both
forward-sexp and backward-sexp functionality, and that it
will naturally work on syntactically incorrect code without any extra
effort. The downside is that it also means that most programming
languages cannot be parsed correctly using SMIE, at least not without
resorting to some special tricks (see SMIE Tricks).
SMIE is meant to be a one-stop shop for structural navigation and
various other features which rely on the syntactic structure of code, in
particular automatic indentation. The main entry point is
smie-setup which is a function typically called while setting
up a major mode.
Setup SMIE navigation and indentation. grammar is a grammar table generated by
smie-prec2->grammar. rules-function is a set of indentation rules for use onsmie-rules-function. keywords are additional arguments, which can include the following keywords:
:forward-tokenfun: Specify the forward lexer to use.:backward-tokenfun: Specify the backward lexer to use.
Calling this function is sufficient to make commands such as
forward-sexp, backward-sexp, and transpose-sexps be
able to properly handle structural elements other than just the paired
parentheses already handled by syntax tables. For example, if the
provided grammar is precise enough, transpose-sexps can correctly
transpose the two arguments of a + operator, taking into account
the precedence rules of the language.
Calling smie-setup is also sufficient to make TAB indentation work in
the expected way, extends blink-matching-paren to apply to
elements like begin...end, and provides some commands that you
can bind in the major mode keymap.
This command closes the most recently opened (and not yet closed) block.
This command is like
down-listbut it also pays attention to nesting of tokens other than parentheses, such asbegin...end.
SMIE's precedence grammars simply give to each token a pair of
precedences: the left-precedence and the right-precedence. We say
T1 < T2 if the right-precedence of token T1 is less than
the left-precedence of token T2. A good way to read this
< is as a kind of parenthesis: if we find ... T1 something
T2 ... then that should be parsed as ... T1 (something T2 ...
rather than as ... T1 something) T2 .... The latter
interpretation would be the case if we had T1 > T2. If we have
T1 = T2, it means that token T2 follows token T1 in the same
syntactic construction, so typically we have "begin" = "end".
Such pairs of precedences are sufficient to express left-associativity
or right-associativity of infix operators, nesting of tokens like
parentheses and many other cases.
This function takes a prec2 grammar table and returns an alist suitable for use in
smie-setup. The prec2 table is itself meant to be built by one of the functions below.
This function takes several prec2 tables and merges them into a new prec2 table.
This function builds a prec2 table from a table of precedences precs. precs should be a list, sorted by precedence (for example
"+"will come before"*"), of elements of the form(assoc op...), where each op is a token that acts as an operator; assoc is their associativity, which can be eitherleft,right,assoc, ornonassoc. All operators in a given element share the same precedence level and associativity.
This function lets you specify the grammar using a BNF notation. It accepts a bnf description of the grammar along with a set of conflict resolution rules resolvers, and returns a prec2 table.
bnf is a list of nonterminal definitions of the form
(nonterm rhs1 rhs2...)where each rhs is a (non-empty) list of terminals (aka tokens) or non-terminals.Not all grammars are accepted:
- An rhs cannot be an empty list (an empty list is never needed, since SMIE allows all non-terminals to match the empty string anyway).
- An rhs cannot have 2 consecutive non-terminals: each pair of non-terminals needs to be separated by a terminal (aka token). This is a fundamental limitation of operator precedence grammars.
Additionally, conflicts can occur:
- The returned prec2 table holds constraints between pairs of tokens, and for any given pair only one constraint can be present: T1 < T2, T1 = T2, or T1 > T2.
- A token can be an
opener(something similar to an open-paren), acloser(like a close-paren), orneitherof the two (e.g., an infix operator, or an inner token like"else").Precedence conflicts can be resolved via resolvers, which is a list of precs tables (see
smie-precs->prec2): for each precedence conflict, if thoseprecstables specify a particular constraint, then the conflict is resolved by using this constraint instead, else a conflict is reported and one of the conflicting constraints is picked arbitrarily and the others are simply ignored.
The usual way to define the SMIE grammar of a language is by defining a new global variable that holds the precedence table by giving a set of BNF rules. For example, the grammar definition for a small Pascal-like language could look like:
(require 'smie)
(defvar sample-smie-grammar
(smie-prec2->grammar
(smie-bnf->prec2
'((id)
(inst ("begin" insts "end")
("if" exp "then" inst "else" inst)
(id ":=" exp)
(exp))
(insts (insts ";" insts) (inst))
(exp (exp "+" exp)
(exp "*" exp)
("(" exps ")"))
(exps (exps "," exps) (exp)))
'((assoc ";"))
'((assoc ","))
'((assoc "+") (assoc "*")))))
A few things to note:
begin ... end blocks
to appear anywhere anyway.
id has no right hand side: this does not
mean that it can match only the empty string, since as mentioned any
sequence of sexps can appear anywhere anyway.
";" as a statement separator instead,
which SMIE can handle very well.
"," and ";" above)
are best defined with BNF rules such as (foo (foo "separator" foo) ...)
which generate precedence conflicts which are then resolved by giving
them an explicit (assoc "separator").
("(" exps ")") rule was not needed to pair up parens, since
SMIE will pair up any characters that are marked as having paren syntax
in the syntax table. What this rule does instead (together with the
definition of exps) is to make it clear that "," should
not appear outside of parentheses.
left or
right, it is usually preferable to mark operators as associative,
using assoc. For that reason "+" and "*" are
defined above as assoc, although the language defines them
formally as left associative.
SMIE comes with a predefined lexical analyzer which uses syntax tables
in the following way: any sequence of characters that have word or
symbol syntax is considered a token, and so is any sequence of
characters that have punctuation syntax. This default lexer is
often a good starting point but is rarely actually correct for any given
language. For example, it will consider "2,+3" to be composed
of 3 tokens: "2", ",+", and "3".
To describe the lexing rules of your language to SMIE, you need 2 functions, one to fetch the next token, and another to fetch the previous token. Those functions will usually first skip whitespace and comments and then look at the next chunk of text to see if it is a special token. If so it should skip the token and return a description of this token. Usually this is simply the string extracted from the buffer, but it can be anything you want. For example:
(defvar sample-keywords-regexp
(regexp-opt '("+" "*" "," ";" ">" ">=" "<" "<=" ":=" "=")))
(defun sample-smie-forward-token ()
(forward-comment (point-max))
(cond
((looking-at sample-keywords-regexp)
(goto-char (match-end 0))
(match-string-no-properties 0))
(t (buffer-substring-no-properties
(point)
(progn (skip-syntax-forward "w_")
(point))))))
(defun sample-smie-backward-token ()
(forward-comment (- (point)))
(cond
((looking-back sample-keywords-regexp (- (point) 2) t)
(goto-char (match-beginning 0))
(match-string-no-properties 0))
(t (buffer-substring-no-properties
(point)
(progn (skip-syntax-backward "w_")
(point))))))
Notice how those lexers return the empty string when in front of
parentheses. This is because SMIE automatically takes care of the
parentheses defined in the syntax table. More specifically if the lexer
returns nil or an empty string, SMIE tries to handle the corresponding
text as a sexp according to syntax tables.
The parsing technique used by SMIE does not allow tokens to behave differently in different contexts. For most programming languages, this manifests itself by precedence conflicts when converting the BNF grammar.
Sometimes, those conflicts can be worked around by expressing the grammar slightly differently. For example, for Modula-2 it might seem natural to have a BNF grammar that looks like this:
...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")
("CASE" exp "OF" cases "END")
...)
(cases (cases "|" cases)
(caselabel ":" insts)
("ELSE" insts))
...
But this will create conflicts for "ELSE": on the one hand, the
IF rule implies (among many other things) that "ELSE" = "END";
but on the other hand, since "ELSE" appears within cases,
which appears left of "END", we also have "ELSE" > "END".
We can solve the conflict either by using:
...
(inst ("IF" exp "THEN" insts "ELSE" insts "END")
("CASE" exp "OF" cases "END")
("CASE" exp "OF" cases "ELSE" insts "END")
...)
(cases (cases "|" cases) (caselabel ":" insts))
...
or
...
(inst ("IF" exp "THEN" else "END")
("CASE" exp "OF" cases "END")
...)
(else (insts "ELSE" insts))
(cases (cases "|" cases) (caselabel ":" insts) (else))
...
Reworking the grammar to try and solve conflicts has its downsides, tho, because SMIE assumes that the grammar reflects the logical structure of the code, so it is preferable to keep the BNF closer to the intended abstract syntax tree.
Other times, after careful consideration you may conclude that those
conflicts are not serious and simply resolve them via the
resolvers argument of smie-bnf->prec2. Usually this is
because the grammar is simply ambiguous: the conflict does not affect
the set of programs described by the grammar, but only the way those
programs are parsed. This is typically the case for separators and
associative infix operators, where you want to add a resolver like
'((assoc "|")). Another case where this can happen is for the
classic dangling else problem, where you will use '((assoc
"else" "then")). It can also happen for cases where the conflict is
real and cannot really be resolved, but it is unlikely to pose a problem
in practice.
Finally, in many cases some conflicts will remain despite all efforts to
restructure the grammar. Do not despair: while the parser cannot be
made more clever, you can make the lexer as smart as you want. So, the
solution is then to look at the tokens involved in the conflict and to
split one of those tokens into 2 (or more) different tokens. E.g., if
the grammar needs to distinguish between two incompatible uses of the
token "begin", make the lexer return different tokens (say
"begin-fun" and "begin-plain") depending on which kind of
"begin" it finds. This pushes the work of distinguishing the
different cases to the lexer, which will thus have to look at the
surrounding text to find ad-hoc clues.
Based on the provided grammar, SMIE will be able to provide automatic indentation without any extra effort. But in practice, this default indentation style will probably not be good enough. You will want to tweak it in many different cases.
SMIE indentation is based on the idea that indentation rules should be
as local as possible. To this end, it relies on the idea of
virtual indentation, which is the indentation that a particular
program point would have if it were at the beginning of a line.
Of course, if that program point is indeed at the beginning of a line,
its virtual indentation is its current indentation. But if not, then
SMIE uses the indentation algorithm to compute the virtual indentation
of that point. Now in practice, the virtual indentation of a program
point does not have to be identical to the indentation it would have if
we inserted a newline before it. To see how this works, the SMIE rule
for indentation after a { in C does not care whether the
{ is standing on a line of its own or is at the end of the
preceding line. Instead, these different cases are handled in the
indentation rule that decides how to indent before a {.
Another important concept is the notion of parent: The
parent of a token, is the head token of the nearest enclosing
syntactic construct. For example, the parent of an else is the
if to which it belongs, and the parent of an if, in turn,
is the lead token of the surrounding construct. The command
backward-sexp jumps from a token to its parent, but there are
some caveats: for openers (tokens which start a construct, like
if), you need to start with point before the token, while for
others you need to start with point after the token.
backward-sexp stops with point before the parent token if that is
the opener of the token of interest, and otherwise it stops with
point after the parent token.
SMIE indentation rules are specified using a function that takes two arguments method and arg where the meaning of arg and the expected return value depend on method.
method can be:
:after, in which case arg is a token and the function
should return the offset to use for indentation after arg.
:before, in which case arg is a token and the function
should return the offset to use to indent arg itself.
:elem, in which case the function should return either the offset
to use to indent function arguments (if arg is the symbol
arg) or the basic indentation step (if arg is the symbol
basic).
:list-intro, in which case arg is a token and the function
should return non-nil if the token is followed by a list of
expressions (not separated by any token) rather than an expression.
When arg is a token, the function is called with point just before
that token. A return value of nil always means to fallback on the
default behavior, so the function should return nil for arguments it
does not expect.
offset can be:
nil: use the default indentation rule.
(column . column): indent to column column.
:after and its parent for :before.
SMIE provides various functions designed specifically for use in the
indentation rules function (several of those functions break if used in
another context). These functions all start with the prefix
smie-rule-.
Return non-
nilif the current token is hanging. A token is hanging if it is the last token on the line and if it is preceded by other tokens: a lone token on a line is not hanging.
Return non-
nilif the current token's parent is among parents.
Return non-
nilif the current token's parent is actually a sibling. This is the case for example when the parent of a","is just the previous",".
Return the proper offset to align the current token with the parent. If non-
nil, offset should be an integer giving an additional offset to apply.
Indent current token as a separator.
By separator, we mean here a token whose sole purpose is to separate various elements within some enclosing syntactic construct, and which does not have any semantic significance in itself (i.e., it would typically not exist as a node in an abstract syntax tree).
Such a token is expected to have an associative syntax and be closely tied to its syntactic parent. Typical examples are
","in lists of arguments (enclosed inside parentheses), or";"in sequences of instructions (enclosed in a{...}orbegin...endblock).method should be the method name that was passed to
smie-rules-function.
Here is an example of an indentation function:
(defun sample-smie-rules (kind token)
(pcase (cons kind token)
(`(:elem . basic) sample-indent-basic)
(`(,_ . ",") (smie-rule-separator kind))
(`(:after . ":=") sample-indent-basic)
(`(:before . ,(or `"begin" `"(" `"{")))
(if (smie-rule-hanging-p) (smie-rule-parent)))
(`(:before . "if")
(and (not (smie-rule-bolp)) (smie-rule-prev-p "else")
(smie-rule-parent)))))
A few things to note:
sample-indent-basic is nil, then SMIE uses the global
setting smie-indent-basic. The major mode could have set
smie-indent-basic buffer-locally instead, but that
is discouraged.
"," make SMIE try to be more clever when
the comma separator is placed at the beginning of lines. It tries to
outdent the separator so as to align the code after the comma; for
example:
x = longfunctionname (
arg1
, arg2
);
":=" exists because otherwise
SMIE would treat ":=" as an infix operator and would align the
right argument with the left one.
"begin" is an example of the use
of virtual indentation: This rule is used only when "begin" is
hanging, which can happen only when "begin" is not at the
beginning of a line. So this is not used when indenting
"begin" itself but only when indenting something relative to this
"begin". Concretely, this rule changes the indentation from:
if x > 0 then begin
dosomething(x);
end
to
if x > 0 then begin
dosomething(x);
end
"if" is similar to the one for
"begin", but where the purpose is to treat "else if"
as a single unit, so as to align a sequence of tests rather than indent
each test further to the right. This function does this only in the
case where the "if" is not placed on a separate line, hence the
smie-rule-bolp test.
If we know that the "else" is always aligned with its "if"
and is always at the beginning of a line, we can use a more efficient
rule:
((equal token "if")
(and (not (smie-rule-bolp))
(smie-rule-prev-p "else")
(save-excursion
(sample-smie-backward-token)
(cons 'column (current-column)))))
The advantage of this formulation is that it reuses the indentation of
the previous "else", rather than going all the way back to the
first "if" of the sequence.
If you are using a mode whose indentation is provided by SMIE, you can
customize the indentation to suit your preferences. You can do this
on a per-mode basis (using the option smie-config), or a
per-file basis (using the function smie-config-local in a
file-local variable specification).
This option lets you customize indentation on a per-mode basis. It is an alist with elements of the form
(mode.rules). For the precise form of rules, see the variable's documentation; but you may find it easier to use the commandsmie-config-guess.
This command tries to work out appropriate settings to produce your preferred style of indentation. Simply call the command while visiting a file that is indented with your style.
Call this command after using
smie-config-guess, to save your settings for future sessions.
This command displays the rules that are used to indent the current line.
This command adds a local rule to adjust the indentation of the current line.
This function adds rules as indentation rules for the current buffer. These add to any mode-specific rules defined by the
smie-configoption. To specify custom indentation rules for a specific file, add an entry to the file's local variables of the form:eval: (smie-config-local '(rules)).
Desktop Save Mode is a feature to save the state of Emacs from one session to another. The user-level commands for using Desktop Save Mode are described in the GNU Emacs Manual (see Saving Emacs Sessions). Modes whose buffers visit a file, don't have to do anything to use this feature.
For buffers not visiting a file to have their state saved, the major
mode must bind the buffer local variable desktop-save-buffer to
a non-nil value.
If this buffer-local variable is non-
nil, the buffer will have its state saved in the desktop file at desktop save. If the value is a function, it is called at desktop save with argument desktop-dirname, and its value is saved in the desktop file along with the state of the buffer for which it was called. When file names are returned as part of the auxiliary information, they should be formatted using the call(desktop-file-name file-name desktop-dirname)
For buffers not visiting a file to be restored, the major mode must
define a function to do the job, and that function must be listed in
the alist desktop-buffer-mode-handlers.
Alist with elements
(major-mode . restore-buffer-function)The function restore-buffer-function will be called with argument list
(buffer-file-name buffer-name desktop-buffer-misc)and it should return the restored buffer. Here desktop-buffer-misc is the value returned by the function optionally bound to
desktop-save-buffer.
GNU Emacs has convenient built-in help facilities, most of which derive their information from documentation strings associated with functions and variables. This chapter describes how to access documentation strings in Lisp programs.
The contents of a documentation string should follow certain conventions. In particular, its first line should be a complete sentence (or two complete sentences) that briefly describes what the function or variable does. See Documentation Tips, for how to write good documentation strings.
Note that the documentation strings for Emacs are not the same thing as the Emacs manual. Manuals have their own source files, written in the Texinfo language; documentation strings are specified in the definitions of the functions and variables they apply to. A collection of documentation strings is not sufficient as a manual because a good manual is not organized in that fashion; it is organized in terms of topics of discussion.
For commands to display documentation strings, see Help.
A documentation string is written using the Lisp syntax for strings, with double-quote characters surrounding the text. It is, in fact, an actual Lisp string. When the string appears in the proper place in a function or variable definition, it serves as the function's or variable's documentation.
In a function definition (a lambda or defun form), the
documentation string is specified after the argument list, and is
normally stored directly in the function object. See Function Documentation. You can also put function documentation in the
function-documentation property of a function name
(see Accessing Documentation).
In a variable definition (a defvar form), the documentation
string is specified after the initial value. See Defining Variables. The string is stored in the variable's
variable-documentation property.
Sometimes, Emacs does not keep documentation strings in memory.
There are two such circumstances. Firstly, to save memory, the
documentation for preloaded functions and variables (including
primitives) is kept in a file named DOC, in the directory
specified by doc-directory (see Accessing Documentation).
Secondly, when a function or variable is loaded from a byte-compiled
file, Emacs avoids loading its documentation string (see Docs and Compilation). In both cases, Emacs looks up the documentation string
from the file only when needed, such as when the user calls C-h
f (describe-function) for a function.
Documentation strings can contain special key substitution sequences, referring to key bindings which are looked up only when the user views the documentation. This allows the help commands to display the correct keys even if a user rearranges the default key bindings. See Keys in Documentation.
In the documentation string of an autoloaded command (see Autoload), these key-substitution sequences have an additional special effect: they cause C-h f on the command to trigger autoloading. (This is needed for correctly setting up the hyperlinks in the *Help* buffer.)
This function returns the documentation string recorded in symbol's property list under property property. It is most often used to look up the documentation strings of variables, for which property is
variable-documentation. However, it can also be used to look up other kinds of documentation, such as for customization groups (but for function documentation, use thedocumentationfunction, below).If the property value refers to a documentation string stored in the DOC file or a byte-compiled file, this function looks up that string and returns it.
If the property value isn't
nil, isn't a string, and doesn't refer to text in a file, then it is evaluated as a Lisp expression to obtain a string.Finally, this function passes the string through
substitute-command-keysto substitute key bindings (see Keys in Documentation). It skips this step if verbatim is non-nil.(documentation-property 'command-line-processed 'variable-documentation) => "Non-nil once command line has been processed" (symbol-plist 'command-line-processed) => (variable-documentation 188902) (documentation-property 'emacs 'group-documentation) => "Customization of the One True Editor."
This function returns the documentation string of function. It handles macros, named keyboard macros, and special forms, as well as ordinary functions.
If function is a symbol, this function first looks for the
function-documentationproperty of that symbol; if that has a non-nilvalue, the documentation comes from that value (if the value is not a string, it is evaluated).If function is not a symbol, or if it has no
function-documentationproperty, thendocumentationextracts the documentation string from the actual function definition, reading it from a file if called for.Finally, unless verbatim is non-
nil, this function callssubstitute-command-keys. The result is the documentation string to return.The
documentationfunction signals avoid-functionerror if function has no function definition. However, it is OK if the function definition has no documentation string. In that case,documentationreturnsnil.
This function returns the documentation string of face as a face.
Here is an example of using the two functions, documentation and
documentation-property, to display the documentation strings for
several symbols in a *Help* buffer.
(defun describe-symbols (pattern)
"Describe the Emacs Lisp symbols matching PATTERN.
All symbols that have PATTERN in their name are described
in the *Help* buffer."
(interactive "sDescribe symbols matching: ")
(let ((describe-func
(function
(lambda (s)
;; Print description of symbol.
(if (fboundp s) ; It is a function.
(princ
(format "%s\t%s\n%s\n\n" s
(if (commandp s)
(let ((keys (where-is-internal s)))
(if keys
(concat
"Keys: "
(mapconcat 'key-description
keys " "))
"Keys: none"))
"Function")
(or (documentation s)
"not documented"))))
(if (boundp s) ; It is a variable.
(princ
(format "%s\t%s\n%s\n\n" s
(if (custom-variable-p s)
"Option " "Variable")
(or (documentation-property
s 'variable-documentation)
"not documented")))))))
sym-list)
;; Build a list of symbols that match pattern.
(mapatoms (function
(lambda (sym)
(if (string-match pattern (symbol-name sym))
(setq sym-list (cons sym sym-list))))))
;; Display the data.
(help-setup-xref (list 'describe-symbols pattern) (interactive-p))
(with-help-window (help-buffer)
(mapcar describe-func (sort sym-list 'string<)))))
The describe-symbols function works like apropos,
but provides more information.
(describe-symbols "goal")
---------- Buffer: *Help* ----------
goal-column Option
Semipermanent goal column for vertical motion, as set by ...
minibuffer-temporary-goal-position Variable
not documented
set-goal-column Keys: C-x C-n
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved to
rather than trying to keep the same horizontal position.
With a non-nil argument ARG, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable ‘goal-column’.
(fn ARG)
temporary-goal-column Variable
Current goal column for vertical motion.
It is the column where point was at the start of the current run
of vertical motion commands.
When moving by visual lines via the function ‘line-move-visual’, it is a cons
cell (COL . HSCROLL), where COL is the x-position, in pixels,
divided by the default column width, and HSCROLL is the number of
columns by which window is scrolled from left margin.
When the ‘track-eol’ feature is doing its job, the value is
‘most-positive-fixnum’.
---------- Buffer: *Help* ----------
This function is used when building Emacs, just before the runnable Emacs is dumped. It finds the positions of the documentation strings stored in the file filename, and records those positions into memory in the function definitions and variable property lists. See Building Emacs.
Emacs reads the file filename from the emacs/etc directory. When the dumped Emacs is later executed, the same file will be looked for in the directory
doc-directory. Usually filename is"DOC".
This variable holds the name of the directory which should contain the file
"DOC"that contains documentation strings for built-in and preloaded functions and variables.In most cases, this is the same as
data-directory. They may be different when you run Emacs from the directory where you built it, without actually installing it. See Definition of data-directory.
When documentation strings refer to key sequences, they should use the
current, actual key bindings. They can do so using certain special text
sequences described below. Accessing documentation strings in the usual
way substitutes current key binding information for these special
sequences. This works by calling substitute-command-keys. You
can also call that function yourself.
Here is a list of the special sequences and what they mean:
\[command]
\{mapvar}
describe-bindings.
\<mapvar>
‘`text-quoting-style.
’'text-quoting-style.
\=Please note: Each `\' must be doubled when written in a string in Emacs Lisp.
The value of this variable is a symbol that specifies the style Emacs should use for single quotes in the wording of help and messages. If the variable's value is
curve, the style is ‘like this’ with curved single quotes. If the value isstraight, the style is 'like this' with straight apostrophes. If the value isgrave, the style is `like this' with grave accent and apostrophe, the standard style before Emacs version 25. The default valuenilacts likecurveif curved single quotes are displayable, and likegraveotherwise.This variable can be used by experts on platforms that have problems with curved quotes. As it is not intended for casual use, it is not a user option.
This function scans string for the above special sequences and replaces them by what they stand for, returning the result as a string. This permits display of documentation that refers accurately to the user's own customized key bindings.
If a command has multiple bindings, this function normally uses the first one it finds. You can specify one particular key binding by assigning an
:advertised-bindingsymbol property to the command, like this:(put 'undo :advertised-binding [?\C-/])The
:advertised-bindingproperty also affects the binding shown in menu items (see Menu Bar). The property is ignored if it specifies a key binding that the command does not actually have.
Here are examples of the special sequences:
(substitute-command-keys
"To abort recursive edit, type `\\[abort-recursive-edit]'.")
=> "To abort recursive edit, type ‘C-]’."
(substitute-command-keys
"The keys that are defined for the minibuffer here are:
\\{minibuffer-local-must-match-map}")
=> "The keys that are defined for the minibuffer here are:
? minibuffer-completion-help
SPC minibuffer-complete-word
TAB minibuffer-complete
C-j minibuffer-complete-and-exit
RET minibuffer-complete-and-exit
C-g abort-recursive-edit
"
(substitute-command-keys
"To abort a recursive edit from the minibuffer, type \
`\\<minibuffer-local-must-match-map>\\[abort-recursive-edit]'.")
=> "To abort a recursive edit from the minibuffer, type ‘C-g’."
There are other special conventions for the text in documentation strings—for instance, you can refer to functions, variables, and sections of this manual. See Documentation Tips, for details.
These functions convert events, key sequences, or characters to textual descriptions. These descriptions are useful for including arbitrary text characters or key sequences in messages, because they convert non-printing and whitespace characters to sequences of printing characters. The description of a non-whitespace printing character is the character itself.
This function returns a string containing the Emacs standard notation for the input events in sequence. If prefix is non-
nil, it is a sequence of input events leading up to sequence and is included in the return value. Both arguments may be strings, vectors or lists. See Input Events, for more information about valid events.(key-description [?\M-3 delete]) => "M-3 <delete>" (key-description [delete] "\M-3") => "M-3 <delete>"See also the examples for
single-key-description, below.
This function returns a string describing event in the standard Emacs notation for keyboard input. A normal printing character appears as itself, but a control character turns into a string starting with `C-', a meta character turns into a string starting with `M-', and space, tab, etc., appear as `SPC', `TAB', etc. A function key symbol appears inside angle brackets `<...>'. An event that is a list appears as the name of the symbol in the car of the list, inside angle brackets.
If the optional argument no-angles is non-
nil, the angle brackets around function keys and event symbols are omitted; this is for compatibility with old versions of Emacs which didn't use the brackets.(single-key-description ?\C-x) => "C-x" (key-description "\C-x \M-y \n \t \r \f123") => "C-x SPC M-y SPC C-j SPC TAB SPC RET SPC C-l 1 2 3" (single-key-description 'delete) => "<delete>" (single-key-description 'C-mouse-1) => "<C-mouse-1>" (single-key-description 'C-mouse-1 t) => "C-mouse-1"
This function returns a string describing character in the standard Emacs notation for characters that appear in text—like
single-key-description, except that control characters are represented with a leading caret (which is how control characters in Emacs buffers are usually displayed). Another difference is thattext-char-descriptionrecognizes the 2**7 bit as the Meta character, whereassingle-key-descriptionuses the 2**27 bit for Meta.(text-char-description ?\C-c) => "^C" (text-char-description ?\M-m) => "\xed" (text-char-description ?\C-\M-m) => "\x8d" (text-char-description (+ 128 ?m)) => "M-m" (text-char-description (+ 128 ?\C-m)) => "M-^M"
This function is used mainly for operating on keyboard macros, but it can also be used as a rough inverse for
key-description. You call it with a string containing key descriptions, separated by spaces; it returns a string or vector containing the corresponding events. (This may or may not be a single valid key sequence, depending on what events you use; see Key Sequences.) If need-vector is non-nil, the return value is always a vector.
Emacs provides a variety of built-in help functions, all accessible to the user as subcommands of the prefix C-h. For more information about them, see Help. Here we describe some program-level interfaces to the same information.
This function finds all meaningful symbols whose names contain a match for the apropos pattern pattern. An apropos pattern is either a word to match, a space-separated list of words of which at least two must match, or a regular expression (if any special regular expression characters occur). A symbol is meaningful if it has a definition as a function, variable, or face, or has properties.
The function returns a list of elements that look like this:
(symbol score function-doc variable-doc plist-doc widget-doc face-doc group-doc)Here, score is an integer measure of how important the symbol seems to be as a match. Each of the remaining elements is a documentation string, or
nil, for symbol as a function, variable, etc.It also displays the symbols in a buffer named *Apropos*, each with a one-line description taken from the beginning of its documentation string.
If do-all is non-
nil, or if the user optionapropos-do-allis non-nil, thenaproposalso shows key bindings for the functions that are found; it also shows all interned symbols, not just meaningful ones (and it lists them in the return value as well).
The value of this variable is a local keymap for characters following the Help key, C-h.
This symbol is not a function; its function definition cell holds the keymap known as
help-map. It is defined in help.el as follows:(define-key global-map (string help-char) 'help-command) (fset 'help-command help-map)
The value of this variable is the help character—the character that Emacs recognizes as meaning Help. By default, its value is 8, which stands for C-h. When Emacs reads this character, if
help-formis a non-nilLisp expression, it evaluates that expression, and displays the result in a window if it is a string.Usually the value of
help-formisnil. Then the help character has no special meaning at the level of command input, and it becomes part of a key sequence in the normal way. The standard key binding of C-h is a prefix key for several general-purpose help features.The help character is special after prefix keys, too. If it has no binding as a subcommand of the prefix key, it runs
describe-prefix-bindings, which displays a list of all the subcommands of the prefix key.
The value of this variable is a list of event types that serve as alternative help characters. These events are handled just like the event specified by
help-char.
If this variable is non-
nil, its value is a form to evaluate whenever the characterhelp-charis read. If evaluating the form produces a string, that string is displayed.A command that calls
read-event,read-char-choice, orread-charprobably should bindhelp-formto a non-nilexpression while it does input. (The time when you should not do this is when C-h has some other meaning.) Evaluating this expression should result in a string that explains what the input is for and how to enter it properly.Entry to the minibuffer binds this variable to the value of
minibuffer-help-form(see Definition of minibuffer-help-form).
This variable holds a function to print help for a prefix key. The function is called when the user types a prefix key followed by the help character, and the help character has no binding after that prefix. The variable's default value is
describe-prefix-bindings.
This function calls
describe-bindingsto display a list of all the subcommands of the prefix key of the most recent key sequence. The prefix described consists of all but the last event of that key sequence. (The last event is, presumably, the help character.)
The following two functions are meant for modes that want to provide help without relinquishing control, such as the electric modes. Their names begin with `Helper' to distinguish them from the ordinary help functions.
This command pops up a window displaying a help buffer containing a listing of all of the key bindings from both the local and global keymaps. It works by calling
describe-bindings.
This command provides help for the current mode. It prompts the user in the minibuffer with the message `Help (Type ? for further options)', and then provides assistance in finding out what the key bindings are, and what the mode is intended for. It returns
nil.
This variable holds the name of the directory in which Emacs finds certain documentation and text files that come with Emacs.
This function returns the name of the help buffer, which is normally *Help*; if such a buffer does not exist, it is first created.
This macro evaluates body like
with-output-to-temp-buffer(see Temporary Displays), inserting any output produced by its forms into a buffer named buffer-name. (Usually, buffer-name should be the value returned by the functionhelp-buffer.) It also puts the specified buffer into Help mode and displays a message telling the user how to quit and scroll the help window. It selects the help window if the current value of the user optionhelp-window-selecthas been set accordingly. It returns the last value in body.
This function updates the cross reference data in the *Help* buffer, which is used to regenerate the help information when the user clicks on the `Back' or `Forward' buttons. Most commands that use the *Help* buffer should invoke this function before clearing the buffer. The item argument should have the form
(function.args), where function is a function to call, with argument list args, to regenerate the help buffer. The interactive-p argument is non-nilif the calling command was invoked interactively; in that case, the stack of items for the *Help* buffer's `Back' buttons is cleared.
See describe-symbols example, for an example of using
help-buffer, with-help-window, and
help-setup-xref.
This macro defines a help command named fname that acts like a prefix key that shows a list of the subcommands it offers.
When invoked, fname displays help-text in a window, then reads and executes a key sequence according to help-map. The string help-text should describe the bindings available in help-map.
The command fname is defined to handle a few events itself, by scrolling the display of help-text. When fname reads one of those special events, it does the scrolling and then reads another event. When it reads an event that is not one of those few, and which has a binding in help-map, it executes that key's binding and then returns.
The argument help-line should be a single-line summary of the alternatives in help-map. In the current version of Emacs, this argument is used only if you set the option
three-step-helptot.This macro is used in the command
help-for-helpwhich is the binding of C-h C-h.
If this variable is non-
nil, commands defined withmake-help-screendisplay their help-line strings in the echo area at first, and display the longer help-text strings only if the user types the help character again.
This chapter describes the Emacs Lisp functions and variables to find, create, view, save, and otherwise work with files and directories. A few other file-related functions are described in Buffers, and those related to backups and auto-saving are described in Backups and Auto-Saving.
Many of the file functions take one or more arguments that are file
names. A file name is a string. Most of these functions expand file
name arguments using the function expand-file-name, so that
~ is handled correctly, as are relative file names (including
../). See File Name Expansion.
In addition, certain magic file names are handled specially. For example, when a remote file name is specified, Emacs accesses the file over the network via an appropriate protocol. See Remote Files. This handling is done at a very low level, so you may assume that all the functions described in this chapter accept magic file names as file name arguments, except where noted. See Magic File Names, for details.
When file I/O functions signal Lisp errors, they usually use the
condition file-error (see Handling Errors). The error
message is in most cases obtained from the operating system, according
to locale system-messages-locale, and decoded using coding system
locale-coding-system (see Locales).
Visiting a file means reading a file into a buffer. Once this is done, we say that the buffer is visiting that file, and call the file the visited file of the buffer.
A file and a buffer are two different things. A file is information recorded permanently in the computer (unless you delete it). A buffer, on the other hand, is information inside of Emacs that will vanish at the end of the editing session (or when you kill the buffer). When a buffer is visiting a file, it contains information copied from the file. The copy in the buffer is what you modify with editing commands. Changes to the buffer do not change the file; to make the changes permanent, you must save the buffer, which means copying the altered buffer contents back into the file.
Despite the distinction between files and buffers, people often refer to a file when they mean a buffer and vice-versa. Indeed, we say, “I am editing a file”, rather than, “I am editing a buffer that I will soon save as a file of the same name”. Humans do not usually need to make the distinction explicit. When dealing with a computer program, however, it is good to keep the distinction in mind.
This section describes the functions normally used to visit files. For historical reasons, these functions have names starting with `find-' rather than `visit-'. See Buffer File Name, for functions and variables that access the visited file name of a buffer or that find an existing buffer by its visited file name.
In a Lisp program, if you want to look at the contents of a file but
not alter it, the fastest way is to use insert-file-contents in a
temporary buffer. Visiting the file is not necessary and takes longer.
See Reading from Files.
This command selects a buffer visiting the file filename, using an existing buffer if there is one, and otherwise creating a new buffer and reading the file into it. It also returns that buffer.
Aside from some technical details, the body of the
find-filefunction is basically equivalent to:(switch-to-buffer (find-file-noselect filename nil nil wildcards))(See
switch-to-bufferin Switching Buffers.)If wildcards is non-
nil, which is always true in an interactive call, thenfind-fileexpands wildcard characters in filename and visits all the matching files.When
find-fileis called interactively, it prompts for filename in the minibuffer.
This command visits filename, like
find-filedoes, but it does not perform any format conversions (see Format Conversion), character code conversions (see Coding Systems), or end-of-line conversions (see End of line conversion). The buffer visiting the file is made unibyte, and its major mode is Fundamental mode, regardless of the file name. File local variable specifications in the file (see File Local Variables) are ignored, and automatic decompression and adding a newline at the end of the file due torequire-final-newline(see require-final-newline) are also disabled.Note that if Emacs already has a buffer visiting the same file non-literally, it will not visit the same file literally, but instead just switch to the existing buffer. If you want to be sure of accessing a file's contents literally, you should create a temporary buffer and then read the file contents into it using
insert-file-contents-literally(see Reading from Files).
This function is the guts of all the file-visiting functions. It returns a buffer visiting the file filename. You may make the buffer current or display it in a window if you wish, but this function does not do so.
The function returns an existing buffer if there is one; otherwise it creates a new buffer and reads the file into it. When
find-file-noselectuses an existing buffer, it first verifies that the file has not changed since it was last visited or saved in that buffer. If the file has changed, this function asks the user whether to reread the changed file. If the user says `yes', any edits previously made in the buffer are lost.Reading the file involves decoding the file's contents (see Coding Systems), including end-of-line conversion, and format conversion (see Format Conversion). If wildcards is non-
nil, thenfind-file-noselectexpands wildcard characters in filename and visits all the matching files.This function displays warning or advisory messages in various peculiar cases, unless the optional argument nowarn is non-
nil. For example, if it needs to create a buffer, and there is no file named filename, it displays the message `(New file)' in the echo area, and leaves the buffer empty.The
find-file-noselectfunction normally callsafter-find-fileafter reading the file (see Subroutines of Visiting). That function sets the buffer major mode, parses local variables, warns the user if there exists an auto-save file more recent than the file just visited, and finishes by running the functions infind-file-hook.If the optional argument rawfile is non-
nil, thenafter-find-fileis not called, and thefind-file-not-found-functionsare not run in case of failure. What's more, a non-nilrawfile value suppresses coding system conversion and format conversion.The
find-file-noselectfunction usually returns the buffer that is visiting the file filename. But, if wildcards are actually used and expanded, it returns a list of buffers that are visiting the various files.(find-file-noselect "/etc/fstab") => #<buffer fstab>
This command selects a buffer visiting the file filename, but does so in a window other than the selected window. It may use another existing window or split a window; see Switching Buffers.
When this command is called interactively, it prompts for filename.
This command selects a buffer visiting the file filename, like
find-file, but it marks the buffer as read-only. See Read Only Buffers, for related functions and variables.When this command is called interactively, it prompts for filename.
If this variable is non-
nil, then the variousfind-filecommands check for wildcard characters and visit all the files that match them (when invoked interactively or when their wildcards argument is non-nil). If this option isnil, then thefind-filecommands ignore their wildcards argument and never treat wildcard characters specially.
The value of this variable is a list of functions to be called after a file is visited. The file's local-variables specification (if any) will have been processed before the hooks are run. The buffer visiting the file is current when the hook functions are run.
This variable is a normal hook. See Hooks.
The value of this variable is a list of functions to be called when
find-fileorfind-file-noselectis passed a nonexistent file name.find-file-noselectcalls these functions as soon as it detects a nonexistent file. It calls them in the order of the list, until one of them returns non-nil.buffer-file-nameis already set up.This is not a normal hook because the values of the functions are used, and in many cases only some of the functions are called.
This buffer-local variable, if set to a non-
nilvalue, makessave-bufferbehave as if the buffer were visiting its file literally, i.e., without conversions of any kind. The commandfind-file-literallysets this variable's local value, but other equivalent functions and commands can do that as well, e.g., to avoid automatic addition of a newline at the end of the file. This variable is permanent local, so it is unaffected by changes of major modes.
The find-file-noselect function uses two important subroutines
which are sometimes useful in user Lisp code: create-file-buffer
and after-find-file. This section explains how to use them.
This function creates a suitably named buffer for visiting filename, and returns it. It uses filename (sans directory) as the name if that name is free; otherwise, it appends a string such as `<2>' to get an unused name. See also Creating Buffers. Note that the uniquify library affects the result of this function. See Uniquify.
Please note:
create-file-bufferdoes not associate the new buffer with a file and does not select the buffer. It also does not use the default major mode.(create-file-buffer "foo") => #<buffer foo> (create-file-buffer "foo") => #<buffer foo<2>> (create-file-buffer "foo") => #<buffer foo<3>>This function is used by
find-file-noselect. It usesgenerate-new-buffer(see Creating Buffers).
This function sets the buffer major mode, and parses local variables (see Auto Major Mode). It is called by
find-file-noselectand by the default revert function (see Reverting).If reading the file got an error because the file does not exist, but its directory does exist, the caller should pass a non-
nilvalue for error. In that case,after-find-fileissues a warning: `(New file)'. For more serious errors, the caller should usually not callafter-find-file.If warn is non-
nil, then this function issues a warning if an auto-save file exists and is more recent than the visited file.If noauto is non-
nil, that says not to enable or disable Auto-Save mode. The mode remains enabled if it was enabled before.If after-find-file-from-revert-buffer is non-
nil, that means this call was fromrevert-buffer. This has no direct effect, but some mode functions and hook functions check the value of this variable.If nomodes is non-
nil, that means don't alter the buffer's major mode, don't process local variables specifications in the file, and don't runfind-file-hook. This feature is used byrevert-bufferin some cases.The last thing
after-find-filedoes is call all the functions in the listfind-file-hook.
When you edit a file in Emacs, you are actually working on a buffer that is visiting that file—that is, the contents of the file are copied into the buffer and the copy is what you edit. Changes to the buffer do not change the file until you save the buffer, which means copying the contents of the buffer into the file.
This function saves the contents of the current buffer in its visited file if the buffer has been modified since it was last visited or saved. Otherwise it does nothing.
save-bufferis responsible for making backup files. Normally, backup-option isnil, andsave-buffermakes a backup file only if this is the first save since visiting the file. Other values for backup-option request the making of backup files in other circumstances:
- With an argument of 4 or 64, reflecting 1 or 3 C-u's, the
save-bufferfunction marks this version of the file to be backed up when the buffer is next saved.- With an argument of 16 or 64, reflecting 2 or 3 C-u's, the
save-bufferfunction unconditionally backs up the previous version of the file before saving it.- With an argument of 0, unconditionally do not make any backup file.
This command saves some modified file-visiting buffers. Normally it asks the user about each buffer. But if save-silently-p is non-
nil, it saves all the file-visiting buffers without querying the user.The optional pred argument controls which buffers to ask about (or to save silently if save-silently-p is non-
nil). If it isnil, that means to ask only about file-visiting buffers. If it ist, that means also offer to save certain other non-file buffers—those that have a non-nilbuffer-local value ofbuffer-offer-save(see Killing Buffers). A user who says `yes' to saving a non-file buffer is asked to specify the file name to use. Thesave-buffers-kill-emacsfunction passes the valuetfor pred.If pred is neither
tnornil, then it should be a function of no arguments. It will be called in each buffer to decide whether to offer to save that buffer. If it returns a non-nilvalue in a certain buffer, that means do offer to save that buffer.
This function writes the current buffer into file filename, makes the buffer visit that file, and marks it not modified. Then it renames the buffer based on filename, appending a string like `<2>' if necessary to make a unique buffer name. It does most of this work by calling
set-visited-file-name(see Buffer File Name) andsave-buffer.If confirm is non-
nil, that means to ask for confirmation before overwriting an existing file. Interactively, confirmation is required, unless the user supplies a prefix argument.If filename is an existing directory, or a symbolic link to one,
write-fileuses the name of the visited file, in directory filename. If the buffer is not visiting a file, it uses the buffer name instead.
Saving a buffer runs several hooks. It also performs format conversion (see Format Conversion).
The value of this variable is a list of functions to be called before writing out a buffer to its visited file. If one of them returns non-
nil, the file is considered already written and the rest of the functions are not called, nor is the usual code for writing the file executed.If a function in
write-file-functionsreturns non-nil, it is responsible for making a backup file (if that is appropriate). To do so, execute the following code:(or buffer-backed-up (backup-buffer))You might wish to save the file modes value returned by
backup-bufferand use that (if non-nil) to set the mode bits of the file that you write. This is whatsave-buffernormally does. See Making Backup Files.The hook functions in
write-file-functionsare also responsible for encoding the data (if desired): they must choose a suitable coding system and end-of-line conversion (see Lisp and Coding Systems), perform the encoding (see Explicit Encoding), and setlast-coding-system-usedto the coding system that was used (see Encoding and I/O).If you set this hook locally in a buffer, it is assumed to be associated with the file or the way the contents of the buffer were obtained. Thus the variable is marked as a permanent local, so that changing the major mode does not alter a buffer-local value. On the other hand, calling
set-visited-file-namewill reset it. If this is not what you want, you might like to usewrite-contents-functionsinstead.Even though this is not a normal hook, you can use
add-hookandremove-hookto manipulate the list. See Hooks.
This works just like
write-file-functions, but it is intended for hooks that pertain to the buffer's contents, not to the particular visited file or its location. Such hooks are usually set up by major modes, as buffer-local bindings for this variable. This variable automatically becomes buffer-local whenever it is set; switching to a new major mode always resets this variable, but callingset-visited-file-namedoes not.If any of the functions in this hook returns non-
nil, the file is considered already written and the rest are not called and neither are the functions inwrite-file-functions.
This normal hook runs before a buffer is saved in its visited file, regardless of whether that is done normally or by one of the hooks described above. For instance, the copyright.el program uses this hook to make sure the file you are saving has the current year in its copyright notice.
This normal hook runs after a buffer has been saved in its visited file. One use of this hook is in Fast Lock mode; it uses this hook to save the highlighting information in a cache file.
If this variable is non-
nil, thensave-bufferprotects against I/O errors while saving by writing the new file to a temporary name instead of the name it is supposed to have, and then renaming it to the intended name after it is clear there are no errors. This procedure prevents problems such as a lack of disk space from resulting in an invalid file.As a side effect, backups are necessarily made by copying. See Rename or Copy. Yet, at the same time, saving a precious file always breaks all hard links between the file you save and other file names.
Some modes give this variable a non-
nilbuffer-local value in particular buffers.
This variable determines whether files may be written out that do not end with a newline. If the value of the variable is
t, thensave-buffersilently adds a newline at the end of the buffer whenever it does not already end in one. If the value isvisit, Emacs adds a missing newline just after it visits the file. If the value isvisit-save, Emacs adds a missing newline both on visiting and on saving. For any other non-nilvalue,save-bufferasks the user whether to add a newline each time the case arises.If the value of the variable is
nil, thensave-bufferdoesn't add newlines at all.nilis the default value, but a few major modes set it totin particular buffers.
See also the function set-visited-file-name (see Buffer File Name).
To copy the contents of a file into a buffer, use the function
insert-file-contents. (Don't use the command
insert-file in a Lisp program, as that sets the mark.)
This function inserts the contents of file filename into the current buffer after point. It returns a list of the absolute file name and the length of the data inserted. An error is signaled if filename is not the name of a file that can be read.
This function checks the file contents against the defined file formats, and converts the file contents if appropriate and also calls the functions in the list
after-insert-file-functions. See Format Conversion. Normally, one of the functions in theafter-insert-file-functionslist determines the coding system (see Coding Systems) used for decoding the file's contents, including end-of-line conversion. However, if the file contains null bytes, it is by default visited without any code conversions. See inhibit-null-byte-detection.If visit is non-
nil, this function additionally marks the buffer as unmodified and sets up various fields in the buffer so that it is visiting the file filename: these include the buffer's visited file name and its last save file modtime. This feature is used byfind-file-noselectand you probably should not use it yourself.If beg and end are non-
nil, they should be numbers that are byte offsets specifying the portion of the file to insert. In this case, visit must benil. For example,(insert-file-contents filename nil 0 500)inserts the first 500 characters of a file.
If the argument replace is non-
nil, it means to replace the contents of the buffer (actually, just the accessible portion) with the contents of the file. This is better than simply deleting the buffer contents and inserting the whole file, because (1) it preserves some marker positions and (2) it puts less data in the undo list.It is possible to read a special file (such as a FIFO or an I/O device) with
insert-file-contents, as long as replace and visit arenil.
This function works like
insert-file-contentsexcept that it does not runfind-file-hook, and does not do format decoding, character code conversion, automatic uncompression, and so on.
If you want to pass a file name to another process so that another
program can read the file, use the function file-local-copy; see
Magic File Names.
You can write the contents of a buffer, or part of a buffer, directly
to a file on disk using the append-to-file and
write-region functions. Don't use these functions to write to
files that are being visited; that could cause confusion in the
mechanisms for visiting.
This function appends the contents of the region delimited by start and end in the current buffer to the end of file filename. If that file does not exist, it is created. This function returns
nil.An error is signaled if filename specifies a nonwritable file, or a nonexistent file in a directory where files cannot be created.
When called from Lisp, this function is completely equivalent to:
(write-region start end filename t)
This function writes the region delimited by start and end in the current buffer into the file specified by filename.
If start is
nil, then the command writes the entire buffer contents (not just the accessible portion) to the file and ignores end.If start is a string, then
write-regionwrites or appends that string, rather than text from the buffer. end is ignored in this case.If append is non-
nil, then the specified text is appended to the existing file contents (if any). If append is a number,write-regionseeks to that byte offset from the start of the file and writes the data from there.If mustbenew is non-
nil, thenwrite-regionasks for confirmation if filename names an existing file. If mustbenew is the symbolexcl, thenwrite-regiondoes not ask for confirmation, but instead it signals an errorfile-already-existsif the file already exists.The test for an existing file, when mustbenew is
excl, uses a special system feature. At least for files on a local disk, there is no chance that some other program could create a file of the same name before Emacs does, without Emacs's noticing.If visit is
t, then Emacs establishes an association between the buffer and the file: the buffer is then visiting that file. It also sets the last file modification time for the current buffer to filename's modtime, and marks the buffer as not modified. This feature is used bysave-buffer, but you probably should not use it yourself.If visit is a string, it specifies the file name to visit. This way, you can write the data to one file (filename) while recording the buffer as visiting another file (visit). The argument visit is used in the echo area message and also for file locking; visit is stored in
buffer-file-name. This feature is used to implementfile-precious-flag; don't use it yourself unless you really know what you're doing.The optional argument lockname, if non-
nil, specifies the file name to use for purposes of locking and unlocking, overriding filename and visit for that purpose.The function
write-regionconverts the data which it writes to the appropriate file formats specified bybuffer-file-formatand also calls the functions in the listwrite-region-annotate-functions. See Format Conversion.Normally,
write-regiondisplays the message `Wrote filename' in the echo area. This message is inhibited if visit is neithertnornilnor a string, or if Emacs is operating in batch mode (see Batch Mode). This feature is useful for programs that use files for internal purposes, files that the user does not need to know about.
The
with-temp-filemacro evaluates the body forms with a temporary buffer as the current buffer; then, at the end, it writes the buffer contents into file file. It kills the temporary buffer when finished, restoring the buffer that was current before thewith-temp-fileform. Then it returns the value of the last form in body.The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).See also
with-temp-bufferin The Current Buffer.
When two users edit the same file at the same time, they are likely to interfere with each other. Emacs tries to prevent this situation from arising by recording a file lock when a file is being modified. Emacs can then detect the first attempt to modify a buffer visiting a file that is locked by another Emacs job, and ask the user what to do. The file lock is really a file, a symbolic link with a special name, stored in the same directory as the file you are editing. (On file systems that do not support symbolic links, a regular file is used.)
When you access files using NFS, there may be a small probability that you and another user will both lock the same file simultaneously. If this happens, it is possible for the two users to make changes simultaneously, but Emacs will still warn the user who saves second. Also, the detection of modification of a buffer visiting a file changed on disk catches some cases of simultaneous editing; see Modification Time.
This function returns
nilif the file filename is not locked. It returnstif it is locked by this Emacs process, and it returns the name of the user who has locked it if it is locked by some other job.(file-locked-p "foo") => nil
This function locks the file filename, if the current buffer is modified. The argument filename defaults to the current buffer's visited file. Nothing is done if the current buffer is not visiting a file, or is not modified, or if the option
create-lockfilesisnil.
This function unlocks the file being visited in the current buffer, if the buffer is modified. If the buffer is not modified, then the file should not be locked, so this function does nothing. It also does nothing if the current buffer is not visiting a file, or is not locked.
This function is called when the user tries to modify file, but it is locked by another user named other-user. The default definition of this function asks the user to say what to do. The value this function returns determines what Emacs does next:
- A value of
tsays to grab the lock on the file. Then this user may edit the file and other-user loses the lock.- A value of
nilsays to ignore the lock and let this user edit the file anyway.- This function may instead signal a
file-lockederror, in which case the change that the user was about to make does not take place.The error message for this error looks like this:
error--> File is locked: file other-userwhere
fileis the name of the file and other-user is the name of the user who has locked the file.If you wish, you can replace the
ask-user-about-lockfunction with your own version that makes the decision in another way.
This section describes the functions for retrieving various types of information about files (or directories or symbolic links), such as whether a file is readable or writable, and its size. These functions all take arguments which are file names. Except where noted, these arguments need to specify existing files, or an error is signaled.
Be careful with file names that end in spaces. On some filesystems (notably, MS-Windows), trailing whitespace characters in file names are silently and automatically ignored.
These functions test for permission to access a file for reading, writing, or execution. Unless explicitly stated otherwise, they recursively follow symbolic links for their file name arguments, at all levels (at the level of the file itself and at all levels of parent directories).
On some operating systems, more complex sets of access permissions can be specified, via mechanisms such as Access Control Lists (ACLs). See Extended Attributes, for how to query and set those permissions.
This function returns
tif a file named filename appears to exist. This does not mean you can necessarily read the file, only that you can find out its attributes. (On Unix and GNU/Linux, this is true if the file exists and you have execute permission on the containing directories, regardless of the permissions of the file itself.)If the file does not exist, or if access control policies prevent you from finding its attributes, this function returns
nil.Directories are files, so
file-exists-preturnstwhen given a directory name. However, symbolic links are treated specially;file-exists-preturnstfor a symbolic link name only if the target file exists.
This function returns
tif a file named filename exists and you can read it. It returnsnilotherwise.
This function returns
tif a file named filename exists and you can execute it. It returnsnilotherwise. On Unix and GNU/Linux, if the file is a directory, execute permission means you can check the existence and attributes of files inside the directory, and open those files if their modes permit.
This function returns
tif the file filename can be written or created by you, andnilotherwise. A file is writable if the file exists and you can write it. It is creatable if it does not exist, but the specified directory does exist and you can write in that directory.In the example below, foo is not writable because the parent directory does not exist, even though the user could create such a directory.
(file-writable-p "~/no-such-dir/foo") => nil
This function returns
tif you have permission to open existing files in the directory whose name as a file is dirname; otherwise (or if there is no such directory), it returnsnil. The value of dirname may be either a directory name (such as /foo/) or the file name of a file which is a directory (such as /foo, without the final slash).For example, from the following we deduce that any attempt to read a file in /foo/ will give an error:
(file-accessible-directory-p "/foo") => nil
This function opens file filename for reading, then closes it and returns
nil. However, if the open fails, it signals an error using string as the error message text.
This function returns
tif deleting the file filename and then creating it anew would keep the file's owner unchanged. It also returnstfor nonexistent files.If the optional argument group is non-
nil, this function also checks that the file's group would be unchanged.If filename is a symbolic link, then, unlike the other functions discussed here,
file-ownership-preserved-pdoes not replace filename with its target. However, it does recursively follow symbolic links at all levels of parent directories.
This function returns the mode bits of filename—an integer summarizing its read, write, and execution permissions. Symbolic links in filename are recursively followed at all levels. If the file does not exist, the return value is
nil.See File permissions, for a description of mode bits. For example, if the low-order bit is 1, the file is executable by all users; if the second-lowest-order bit is 1, the file is writable by all users; etc. The highest possible value is 4095 (7777 octal), meaning that everyone has read, write, and execute permission, the SUID bit is set for both others and group, and the sticky bit is set.
See Changing Files, for the
set-file-modesfunction, which can be used to set these permissions.(file-modes "~/junk/diffs") => 492 ; Decimal integer. (format "%o" 492) => "754" ; Convert to octal. (set-file-modes "~/junk/diffs" #o666) => nil $ ls -l diffs -rw-rw-rw- 1 lewis lewis 3063 Oct 30 16:00 diffsMS-DOS note: On MS-DOS, there is no such thing as an executable file mode bit. So
file-modesconsiders a file executable if its name ends in one of the standard executable extensions, such as .com, .bat, .exe, and some others. Files that begin with the Unix-standard `#!' signature, such as shell and Perl scripts, are also considered executable. Directories are also reported as executable, for compatibility with Unix. These conventions are also followed byfile-attributes(see File Attributes).
This section describes how to distinguish various kinds of files, such as directories, symbolic links, and ordinary files.
If the file filename is a symbolic link, the
file-symlink-pfunction returns its (non-recursive) link target as a string. (The link target string is not necessarily the full absolute file name of the target; determining the full file name that the link points to is nontrivial, see below.) If the leading directories of filename include symbolic links, this function recursively follows them.If the file filename is not a symbolic link, or does not exist,
file-symlink-preturnsnil.Here are a few examples of using this function:
(file-symlink-p "not-a-symlink") => nil (file-symlink-p "sym-link") => "not-a-symlink" (file-symlink-p "sym-link2") => "sym-link" (file-symlink-p "/bin") => "/pub/bin"Note that in the third example, the function returned sym-link, but did not proceed to resolve it, although that file is itself a symbolic link. This is what we meant by “non-recursive” above—the process of following the symbolic links does not recurse if the link target is itself a link.
The string that this function returns is what is recorded in the symbolic link; it may or may not include any leading directories. This function does not expand the link target to produce a fully-qualified file name, and in particular does not use the leading directories, if any, of the filename argument if the link target is not an absolute file name. Here's an example:
(file-symlink-p "/foo/bar/baz") => "some-file"Here, although /foo/bar/baz was given as a fully-qualified file name, the result is not, and in fact does not have any leading directories at all. And since some-file might itself be a symbolic link, you cannot simply prepend leading directories to it, nor even naively use
expand-file-name(see File Name Expansion) to produce its absolute file name.For this reason, this function is seldom useful if you need to determine more than just the fact that a file is or isn't a symbolic link. If you actually need the file name of the link target, use
file-chase-linksorfile-truename, described in Truenames.
The next two functions recursively follow symbolic links at all levels for filename.
This function returns
tif filename is the name of an existing directory,nilotherwise.(file-directory-p "~rms") => t (file-directory-p "~rms/lewis/files.texi") => nil (file-directory-p "~rms/lewis/no-such-file") => nil (file-directory-p "$HOME") => nil (file-directory-p (substitute-in-file-name "$HOME")) => t
This function returns
tif the file filename exists and is a regular file (not a directory, named pipe, terminal, or other I/O device).
The truename of a file is the name that you get by following symbolic links at all levels until none remain, then simplifying away `.' and `..' appearing as name components. This results in a sort of canonical name for the file. A file does not always have a unique truename; the number of distinct truenames a file has is equal to the number of hard links to the file. However, truenames are useful because they eliminate symbolic links as a cause of name variation.
This function returns the truename of the file filename. If the argument is not an absolute file name, this function first expands it against
default-directory.This function does not expand environment variables. Only
substitute-in-file-namedoes that. See Definition of substitute-in-file-name.If you may need to follow symbolic links preceding `..' appearing as a name component, call
file-truenamewithout prior direct or indirect calls toexpand-file-name. Otherwise, the file name component immediately preceding `..' will be simplified away beforefile-truenameis called. To eliminate the need for a call toexpand-file-name,file-truenamehandles `~' in the same way thatexpand-file-namedoes. See Functions that Expand Filenames.
This function follows symbolic links, starting with filename, until it finds a file name which is not the name of a symbolic link. Then it returns that file name. This function does not follow symbolic links at the level of parent directories.
If you specify a number for limit, then after chasing through that many links, the function just returns what it has even if that is still a symbolic link.
To illustrate the difference between file-chase-links and
file-truename, suppose that /usr/foo is a symbolic link to
the directory /home/foo, and /home/foo/hello is an
ordinary file (or at least, not a symbolic link) or nonexistent. Then
we would have:
(file-chase-links "/usr/foo/hello")
;; This does not follow the links in the parent directories.
=> "/usr/foo/hello"
(file-truename "/usr/foo/hello")
;; Assuming that /home is not a symbolic link.
=> "/home/foo/hello"
This function returns
tif the files file1 and file2 name the same file. This is similar to comparing their truenames, except that remote file names are also handled in an appropriate manner. If file1 or file2 does not exist, the return value is unspecified.
This function returns
tif file is a file in directory dir, or in a subdirectory of dir. It also returnstif file and dir are the same directory. It compares the truenames of the two directories. If dir does not name an existing directory, the return value isnil.
This section describes the functions for getting detailed information about a file, including the owner and group numbers, the number of names, the inode number, the size, and the times of access and modification.
This function returns
tif the file filename1 is newer than file filename2. If filename1 does not exist, it returnsnil. If filename1 does exist, but filename2 does not, it returnst.In the following example, assume that the file aug-19 was written on the 19th, aug-20 was written on the 20th, and the file no-file doesn't exist at all.
(file-newer-than-file-p "aug-19" "aug-20") => nil (file-newer-than-file-p "aug-20" "aug-19") => t (file-newer-than-file-p "aug-19" "no-file") => t (file-newer-than-file-p "no-file" "aug-19") => nil
If the filename argument to the next two functions is a symbolic link, then these function do not replace it with its target. However, they both recursively follow symbolic links at all levels of parent directories.
This function returns a list of attributes of file filename. If the specified file cannot be opened, it returns
nil. The optional parameter id-format specifies the preferred format of attributes UID and GID (see below)—the valid values are'stringand'integer. The latter is the default, but we plan to change that, so you should specify a non-nilvalue for id-format if you use the returned UID or GID.The elements of the list, in order, are:
tfor a directory, a string for a symbolic link (the name linked to), ornilfor a text file.- The number of names the file has. Alternate names, also known as hard links, can be created by using the
add-name-to-filefunction (see Changing Files).- The file's UID, normally as a string. However, if it does not correspond to a named user, the value is a number.
- The file's GID, likewise.
- The time of last access, as a list of four integers
(sec-high sec-low microsec picosec). (This is similar to the value ofcurrent-time; see Time of Day.) Note that on some FAT-based filesystems, only the date of last access is recorded, so this time will always hold the midnight of the day of last access.- The time of last modification as a list of four integers (as above). This is the last time when the file's contents were modified.
- The time of last status change as a list of four integers (as above). This is the time of the last change to the file's access mode bits, its owner and group, and other information recorded in the filesystem for the file, beyond the file's contents.
- The size of the file in bytes. This is floating point if the size is too large to fit in a Lisp integer.
- The file's modes, as a string of ten letters or dashes, as in `ls -l'.
- An unspecified value, present for backward compatibility.
- The file's inode number. If possible, this is an integer. If the inode number is too large to be represented as an integer in Emacs Lisp but dividing it by 2^16 yields a representable integer, then the value has the form
(high.low), where low holds the low 16 bits. If the inode number is too wide for even that, the value is of the form(high middle.low), wherehighholds the high bits, middle the middle 24 bits, and low the low 16 bits.- The filesystem number of the device that the file is on. Depending on the magnitude of the value, this can be either an integer or a cons cell, in the same manner as the inode number. This element and the file's inode number together give enough information to distinguish any two files on the system—no two files can have the same values for both of these numbers.
For example, here are the file attributes for files.texi:
(file-attributes "files.texi" 'string) => (nil 1 "lh" "users" (20614 64019 50040 152000) (20000 23 0 0) (20614 64555 902289 872000) 122295 "-rw-rw-rw-" t (5888 2 . 43978) (15479 . 46724))and here is how the result is interpreted:
nil- is neither a directory nor a symbolic link.
1- has only one name (the name files.texi in the current default directory).
"lh"- is owned by the user with name `lh'.
"users"- is in the group with name `users'.
(20614 64019 50040 152000)- was last accessed on October 23, 2012, at 20:12:03.050040152 UTC.
(20000 23 0 0)- was last modified on July 15, 2001, at 08:53:43 UTC.
(20614 64555 902289 872000)- last had its status changed on October 23, 2012, at 20:20:59.902289872 UTC.
122295- is 122295 bytes long. (It may not contain 122295 characters, though, if some of the bytes belong to multibyte sequences, and also if the end-of-line format is CR-LF.)
"-rw-rw-rw-"- has a mode of read and write access for the owner, group, and world.
t- is merely a placeholder; it carries no information.
(5888 2 . 43978)- has an inode number of 6473924464520138.
(15479 . 46724)- is on the file-system device whose number is 1014478468.
This function returns the number of names (i.e., hard links) that file filename has. If the file does not exist, this function returns
nil. Note that symbolic links have no effect on this function, because they are not considered to be names of the files they link to.$ ls -l foo* -rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo -rw-rw-rw- 2 rms rms 4 Aug 19 01:27 foo1 (file-nlinks "foo") => 2 (file-nlinks "doesnt-exist") => nil
On some operating systems, each file can be associated with arbitrary extended file attributes. At present, Emacs supports querying and setting two specific sets of extended file attributes: Access Control Lists (ACLs) and SELinux contexts. These extended file attributes are used, on some systems, to impose more sophisticated file access controls than the basic Unix-style permissions discussed in the previous sections.
A detailed explanation of ACLs and SELinux is beyond the scope of this manual. For our purposes, each file can be associated with an ACL, which specifies its properties under an ACL-based file control system, and/or an SELinux context, which specifies its properties under the SELinux system.
This function returns the ACL for the file filename. The exact Lisp representation of the ACL is unspecified (and may change in future Emacs versions), but it is the same as what
set-file-acltakes for its acl argument (see Changing Files).The underlying ACL implementation is platform-specific; on GNU/Linux and BSD, Emacs uses the POSIX ACL interface, while on MS-Windows Emacs emulates the POSIX ACL interface with native file security APIs.
If Emacs was not compiled with ACL support, or the file does not exist or is inaccessible, or Emacs was unable to determine the ACL entries for any other reason, then the return value is
nil.
This function returns the SELinux context of the file filename, as a list of the form
(user role type range). The list elements are the context's user, role, type, and range respectively, as Lisp strings; see the SELinux documentation for details about what these actually mean. The return value has the same form as whatset-file-selinux-contexttakes for its context argument (see Changing Files).If Emacs was not compiled with SELinux support, or the file does not exist or is inaccessible, or if the system does not support SELinux, then the return value is
(nil nil nil nil).
This function returns an alist of the Emacs-recognized extended attributes of file filename. Currently, it serves as a convenient way to retrieve both the ACL and SELinux context; you can then call the function
set-file-extended-attributes, with the returned alist as its second argument, to apply the same file access attributes to another file (see Changing Files).One of the elements is
(acl .acl), where acl has the same form returned byfile-acl.Another element is
(selinux-context .context), where context is the SELinux context, in the same form returned byfile-selinux-context.
This section explains how to search for a file in a list of directories (a path), or for an executable file in the standard list of executable file directories.
To search for a user-specific configuration file, See Standard File Names, for the locate-user-emacs-file function.
This function searches for a file whose name is filename in a list of directories given by path, trying the suffixes in suffixes. If it finds such a file, it returns the file's absolute file name (see Relative File Names); otherwise it returns
nil.The optional argument suffixes gives the list of file-name suffixes to append to filename when searching.
locate-filetries each possible directory with each of these suffixes. If suffixes isnil, or(""), then there are no suffixes, and filename is used only as-is. Typical values of suffixes areexec-suffixes(see Subprocess Creation),load-suffixes,load-file-rep-suffixesand the return value of the functionget-load-suffixes(see Load Suffixes).Typical values for path are
exec-path(see Subprocess Creation) when looking for executable programs, orload-path(see Library Search) when looking for Lisp files. If filename is absolute, path has no effect, but the suffixes in suffixes are still tried.The optional argument predicate, if non-
nil, specifies a predicate function for testing whether a candidate file is suitable. The predicate is passed the candidate file name as its single argument. If predicate isnilor omitted,locate-fileusesfile-readable-pas the predicate. See Kinds of Files, for other useful predicates, e.g.,file-executable-pandfile-directory-p.For compatibility, predicate can also be one of the symbols
executable,readable,writable,exists, or a list of one or more of these symbols.
This function searches for the executable file of the named program and returns the absolute file name of the executable, including its file-name extensions, if any. It returns
nilif the file is not found. The functions searches in all the directories inexec-path, and tries all the file-name extensions inexec-suffixes(see Subprocess Creation).
The functions in this section rename, copy, delete, link, and set
the modes (permissions) of files. They all signal a file-error
error if they fail to perform their function, reporting the
system-dependent error message that describes the reason for the
failure.
In the functions that have an argument newname, if a file by the name of newname already exists, the actions taken depend on the value of the argument ok-if-already-exists:
file-already-exists error if
ok-if-already-exists is nil.
The next four commands all recursively follow symbolic links at all
levels of parent directories for their first argument, but, if that
argument is itself a symbolic link, then only copy-file
replaces it with its (recursive) target.
This function gives the file named oldname the additional name newname. This means that newname becomes a new hard link to oldname.
In the first part of the following example, we list two files, foo and foo3.
$ ls -li fo* 81908 -rw-rw-rw- 1 rms rms 29 Aug 18 20:32 foo 84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3Now we create a hard link, by calling
add-name-to-file, then list the files again. This shows two names for one file, foo and foo2.(add-name-to-file "foo" "foo2") => nil $ ls -li fo* 81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 2 rms rms 29 Aug 18 20:32 foo2 84302 -rw-rw-rw- 1 rms rms 24 Aug 18 20:31 foo3Finally, we evaluate the following:
(add-name-to-file "foo" "foo3" t)and list the files again. Now there are three names for one file: foo, foo2, and foo3. The old contents of foo3 are lost.
(add-name-to-file "foo1" "foo3") => nil $ ls -li fo* 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo2 81908 -rw-rw-rw- 3 rms rms 29 Aug 18 20:32 foo3This function is meaningless on operating systems where multiple names for one file are not allowed. Some systems implement multiple names by copying the file instead.
See also
file-nlinksin File Attributes.
This command renames the file filename as newname.
If filename has additional names aside from filename, it continues to have those names. In fact, adding the name newname with
add-name-to-fileand then deleting filename has the same effect as renaming, aside from momentary intermediate states.
This command copies the file oldname to newname. An error is signaled if oldname does not exist. If newname names a directory, it copies oldname into that directory, preserving its final name component.
If time is non-
nil, then this function gives the new file the same last-modified time that the old one has. (This works on only some operating systems.) If setting the time gets an error,copy-filesignals afile-date-errorerror. In an interactive call, a prefix argument specifies a non-nilvalue for time.If argument preserve-uid-gid is
nil, we let the operating system decide the user and group ownership of the new file (this is usually set to the user running Emacs). If preserve-uid-gid is non-nil, we attempt to copy the user and group ownership of the file. This works only on some operating systems, and only if you have the correct permissions to do so.If the optional argument preserve-permissions is non-
nil, this function copies the file modes (or “permissions”) of oldname to newname, as well as the Access Control List and SELinux context (if any). See Information about Files.Otherwise, the file modes of newname are left unchanged if it is an existing file, and set to those of oldname, masked by the default file permissions (see
set-default-file-modesbelow), if newname is to be newly created. The Access Control List or SELinux context are not copied over in either case.
This command makes a symbolic link to filename, named newname. This is like the shell command `ln -s filename newname'.
This function is not available on systems that don't support symbolic links.
This command deletes the file filename. If the file has multiple names, it continues to exist under the other names. If filename is a symbolic link,
delete-filedeletes only the symbolic link and not its target (though it does follow symbolic links at all levels of parent directories).A suitable kind of
file-errorerror is signaled if the file does not exist, or is not deletable. (On Unix and GNU/Linux, a file is deletable if its directory is writable.)If the optional argument trash is non-
niland the variabledelete-by-moving-to-trashis non-nil, this command moves the file into the system Trash instead of deleting it. See Miscellaneous File Operations. When called interactively, trash istif no prefix argument is given, andnilotherwise.See also
delete-directoryin Create/Delete Dirs.
This function sets the file mode (or permissions) of filename to mode. It recursively follows symbolic links at all levels for filename.
If called non-interactively, mode must be an integer. Only the lowest 12 bits of the integer are used; on most systems, only the lowest 9 bits are meaningful. You can use the Lisp construct for octal numbers to enter mode. For example,
(set-file-modes #o644)specifies that the file should be readable and writable for its owner, readable for group members, and readable for all other users. See File permissions, for a description of mode bit specifications.
Interactively, mode is read from the minibuffer using
read-file-modes(see below), which lets the user type in either an integer or a string representing the permissions symbolically.See File Attributes, for the function
file-modes, which returns the permissions of a file.
This function sets the default permissions for new files created by Emacs and its subprocesses. Every file created with Emacs initially has these permissions, or a subset of them (
write-regionwill not grant execute permissions even if the default file permissions allow execution). On Unix and GNU/Linux, the default permissions are given by the bitwise complement of the `umask' value.The argument mode should be an integer which specifies the permissions, similar to
set-file-modesabove. Only the lowest 9 bits are meaningful.The default file permissions have no effect when you save a modified version of an existing file; saving a file preserves its existing permissions.
This macro evaluates the body forms with the default permissions for new files temporarily set to modes (whose value is as for
set-file-modesabove). When finished, it restores the original default file permissions, and returns the value of the last form in body.This is useful for creating private files, for example.
This function reads a set of file mode bits from the minibuffer. The first optional argument prompt specifies a non-default prompt. Second second optional argument base-file is the name of a file on whose permissions to base the mode bits that this function returns, if what the user types specifies mode bits relative to permissions of an existing file.
If user input represents an octal number, this function returns that number. If it is a complete symbolic specification of mode bits, as in
"u=rwx", the function converts it to the equivalent numeric value usingfile-modes-symbolic-to-numberand returns the result. If the specification is relative, as in"o+g", then the permissions on which the specification is based are taken from the mode bits of base-file. If base-file is omitted ornil, the function uses0as the base mode bits. The complete and relative specifications can be combined, as in"u+r,g+rx,o+r,g-w". See File permissions, for a description of file mode specifications.
This function converts a symbolic file mode specification in modes into the equivalent integer. If the symbolic specification is based on an existing file, that file's mode bits are taken from the optional argument base-modes; if that argument is omitted or
nil, it defaults to 0, i.e., no access rights at all.
This function sets the access and modification times of filename to time. The return value is
tif the times are successfully set, otherwise it isnil. time defaults to the current time and must be in the format returned bycurrent-time(see Time of Day).
This function sets the Emacs-recognized extended file attributes for
filename. The second argument attribute-alist should be an alist of the same form returned byfile-extended-attributes. The return value istif the attributes are successfully set, otherwise it isnil. See Extended Attributes.
This function sets the SELinux security context for filename to context. The context argument should be a list
(user role type range), where each element is a string. See Extended Attributes.The function returns
tif it succeeds in setting the SELinux context of filename. It returnsnilif the context was not set (e.g., if SELinux is disabled, or if Emacs was compiled without SELinux support).
This function sets the Access Control List for filename to acl. The acl argument should have the same form returned by the function
file-acl. See Extended Attributes.The function returns
tif it successfully sets the ACL of filename,nilotherwise.
Files are generally referred to by their names, in Emacs as elsewhere. File names in Emacs are represented as strings. The functions that operate on a file all expect a file name argument.
In addition to operating on files themselves, Emacs Lisp programs often need to operate on file names; i.e., to take them apart and to use part of a name to construct related file names. This section describes how to manipulate file names.
The functions in this section do not actually access files, so they can operate on file names that do not refer to an existing file or directory.
On MS-DOS and MS-Windows, these functions (like the function that actually operate on files) accept MS-DOS or MS-Windows file-name syntax, where backslashes separate the components, as well as Unix syntax; but they always return Unix syntax. This enables Lisp programs to specify file names in Unix syntax and work properly on all systems without change.13
The operating system groups files into directories. To specify a file, you must specify the directory and the file's name within that directory. Therefore, Emacs considers a file name as having two main parts: the directory name part, and the nondirectory part (or file name within the directory). Either part may be empty. Concatenating these two parts reproduces the original file name.
On most systems, the directory part is everything up to and including the last slash (backslash is also allowed in input on MS-DOS or MS-Windows); the nondirectory part is the rest.
For some purposes, the nondirectory part is further subdivided into the name proper and the version number. On most systems, only backup files have version numbers in their names.
This function returns the directory part of filename, as a directory name (see Directory Names), or
nilif filename does not include a directory part.On GNU and Unix systems, a string returned by this function always ends in a slash. On MS-DOS it can also end in a colon.
(file-name-directory "lewis/foo") ; Unix example => "lewis/" (file-name-directory "foo") ; Unix example => nil
This function returns the nondirectory part of filename.
(file-name-nondirectory "lewis/foo") => "foo" (file-name-nondirectory "foo") => "foo" (file-name-nondirectory "lewis/") => ""
This function returns filename with any file version numbers, backup version numbers, or trailing tildes discarded.
If keep-backup-version is non-
nil, then true file version numbers understood as such by the file system are discarded from the return value, but backup version numbers are kept.(file-name-sans-versions "~rms/foo.~1~") => "~rms/foo" (file-name-sans-versions "~rms/foo~") => "~rms/foo" (file-name-sans-versions "~rms/foo") => "~rms/foo"
This function returns filename's final extension, if any, after applying
file-name-sans-versionsto remove any version/backup part. The extension, in a file name, is the part that follows the last `.' in the last name component (minus any version/backup part).This function returns
nilfor extensionless file names such as foo. It returns""for null extensions, as in foo.. If the last component of a file name begins with a `.', that `.' doesn't count as the beginning of an extension. Thus, .emacs's extension isnil, not `.emacs'.If period is non-
nil, then the returned value includes the period that delimits the extension, and if filename has no extension, the value is"".
This function returns filename minus its extension, if any. The version/backup part, if present, is only removed if the file has an extension. For example,
(file-name-sans-extension "foo.lose.c") => "foo.lose" (file-name-sans-extension "big.hack/foo") => "big.hack/foo" (file-name-sans-extension "/my/home/.emacs") => "/my/home/.emacs" (file-name-sans-extension "/my/home/.emacs.el") => "/my/home/.emacs" (file-name-sans-extension "~/foo.el.~3~") => "~/foo" (file-name-sans-extension "~/foo.~3~") => "~/foo.~3~"Note that the `.~3~' in the two last examples is the backup part, not an extension.
This function is the composition of
file-name-sans-extensionandfile-name-nondirectory. For example,(file-name-base "/my/home/foo.c") => "foo"The filename argument defaults to
buffer-file-name.
All the directories in the file system form a tree starting at the root directory. A file name can specify all the directory names starting from the root of the tree; then it is called an absolute file name. Or it can specify the position of the file in the tree relative to a default directory; then it is called a relative file name. On Unix and GNU/Linux, an absolute file name starts with a `/' or a `~' (see abbreviate-file-name), and a relative one does not. On MS-DOS and MS-Windows, an absolute file name starts with a slash or a backslash, or with a drive specification `x:/', where x is the drive letter.
This function returns
tif file filename is an absolute file name,nilotherwise.(file-name-absolute-p "~rms/foo") => t (file-name-absolute-p "rms/foo") => nil (file-name-absolute-p "/user/rms/foo") => t
Given a possibly relative file name, you can convert it to an
absolute name using expand-file-name (see File Name Expansion). This function converts absolute file names to relative
names:
This function tries to return a relative name that is equivalent to filename, assuming the result will be interpreted relative to directory (an absolute directory name or directory file name). If directory is omitted or
nil, it defaults to the current buffer's default directory.On some operating systems, an absolute file name begins with a device name. On such systems, filename has no relative equivalent based on directory if they start with two different device names. In this case,
file-relative-namereturns filename in absolute form.(file-relative-name "/foo/bar" "/foo/") => "bar" (file-relative-name "/foo/bar" "/hack/") => "../foo/bar"
A directory name is the name of a directory. A directory is actually a kind of file, so it has a file name (called the directory file name, which is related to the directory name but not identical to it. (This is not quite the same as the usual Unix terminology.) These two different names for the same entity are related by a syntactic transformation. On GNU and Unix systems, this is simple: a directory name ends in a slash, whereas the directory file name lacks that slash. On MS-DOS the relationship is more complicated.
The difference between directory name and directory file name is
subtle but crucial. When an Emacs variable or function argument is
described as being a directory name, a directory file name is not
acceptable. When file-name-directory returns a string, that is
always a directory name.
The following two functions convert between directory names and directory file names. They do nothing special with environment variable substitutions such as `$HOME', and the constructs `~', `.' and `..'.
This function returns a string representing filename in a form that the operating system will interpret as the name of a directory (a directory name). On most systems, this means appending a slash to the string (if it does not already end in one).
(file-name-as-directory "~rms/lewis") => "~rms/lewis/"
This function returns non-
nilif filename ends with a directory separator character. This is the forward slash `/' on Unix and GNU systems; MS-Windows and MS-DOS recognize both the forward slash and the backslash `\' as directory separators.
This function returns a string representing dirname in a form that the operating system will interpret as the name of a file (a directory file name). On most systems, this means removing the final slash (or backslash) from the string.
(directory-file-name "~lewis/") => "~lewis"
Given a directory name, you can combine it with a relative file name
using concat:
(concat dirname relfile)
Be sure to verify that the file name is relative before doing that. If you use an absolute file name, the results could be syntactically invalid or refer to the wrong file.
If you want to use a directory file name in making such a
combination, you must first convert it to a directory name using
file-name-as-directory:
(concat (file-name-as-directory dirfile) relfile)
Don't try concatenating a slash by hand, as in
;;; Wrong!
(concat dirfile "/" relfile)
because this is not portable. Always use
file-name-as-directory.
To avoid the issues mentioned above, or if the dirname value
might be nil (for example, from an element of load-path), use:
(expand-file-name relfile dirname)
To convert a directory name to its abbreviation, use this function:
This function returns an abbreviated form of filename. It applies the abbreviations specified in
directory-abbrev-alist(see File Aliases), then substitutes `~' for the user's home directory if the argument names a file in the home directory or one of its subdirectories. If the home directory is a root directory, it is not replaced with `~', because this does not make the result shorter on many systems.You can use this function for directory names and for file names, because it recognizes abbreviations even as part of the name.
Expanding a file name means converting a relative file name to an absolute one. Since this is done relative to a default directory, you must specify the default directory name as well as the file name to be expanded. It also involves expanding abbreviations like ~/ (see abbreviate-file-name), and eliminating redundancies like ./ and name/../.
This function converts filename to an absolute file name. If directory is supplied, it is the default directory to start with if filename is relative. (The value of directory should itself be an absolute directory name or directory file name; it may start with `~'.) Otherwise, the current buffer's value of
default-directoryis used. For example:(expand-file-name "foo") => "/xcssun/users/rms/lewis/foo" (expand-file-name "../foo") => "/xcssun/users/rms/foo" (expand-file-name "foo" "/usr/spool/") => "/usr/spool/foo"If the part of the combined file name before the first slash is `~', it expands to the value of the HOME environment variable (usually your home directory). If the part before the first slash is `~user' and if user is a valid login name, it expands to user's home directory.
Filenames containing `.' or `..' are simplified to their canonical form:
(expand-file-name "bar/../foo") => "/xcssun/users/rms/lewis/foo"In some cases, a leading `..' component can remain in the output:
(expand-file-name "../home" "/") => "/../home"This is for the sake of filesystems that have the concept of a superroot above the root directory /. On other filesystems, /../ is interpreted exactly the same as /.
Note that
expand-file-namedoes not expand environment variables; onlysubstitute-in-file-namedoes that:(expand-file-name "$HOME/foo") => "/xcssun/users/rms/lewis/$HOME/foo"Note also that
expand-file-namedoes not follow symbolic links at any level. This results in a difference between the wayfile-truenameandexpand-file-nametreat `..'. Assuming that `/tmp/bar' is a symbolic link to the directory `/tmp/foo/bar' we get:(file-truename "/tmp/bar/../myfile") => "/tmp/foo/myfile" (expand-file-name "/tmp/bar/../myfile") => "/tmp/myfile"If you may need to follow symbolic links preceding `..', you should make sure to call
file-truenamewithout prior direct or indirect calls toexpand-file-name. See Truenames.
The value of this buffer-local variable is the default directory for the current buffer. It should be an absolute directory name; it may start with `~'. This variable is buffer-local in every buffer.
expand-file-nameuses the default directory when its second argument isnil.The value is always a string ending with a slash.
default-directory => "/user/lewis/manual/"
This function replaces environment variable references in filename with the environment variable values. Following standard Unix shell syntax, `$' is the prefix to substitute an environment variable value. If the input contains `$$', that is converted to `$'; this gives the user a way to quote a `$'.
The environment variable name is the series of alphanumeric characters (including underscores) that follow the `$'. If the character following the `$' is a `{', then the variable name is everything up to the matching `}'.
Calling
substitute-in-file-nameon output produced bysubstitute-in-file-nametends to give incorrect results. For instance, use of `$$' to quote a single `$' won't work properly, and `$' in an environment variable's value could lead to repeated substitution. Therefore, programs that call this function and put the output where it will be passed to this function need to double all `$' characters to prevent subsequent incorrect results.Here we assume that the environment variable HOME, which holds the user's home directory name, has value `/xcssun/users/rms'.
(substitute-in-file-name "$HOME/foo") => "/xcssun/users/rms/foo"After substitution, if a `~' or a `/' appears immediately after another `/', the function discards everything before it (up through the immediately preceding `/').
(substitute-in-file-name "bar/~/foo") => "~/foo" (substitute-in-file-name "/usr/local/$HOME/foo") => "/xcssun/users/rms/foo" ;; /usr/local/ has been discarded.
Some programs need to write temporary files. Here is the usual way to construct a name for such a file:
(make-temp-file name-of-application)
The job of make-temp-file is to prevent two different users or
two different jobs from trying to use the exact same file name.
This function creates a temporary file and returns its name. Emacs creates the temporary file's name by adding to prefix some random characters that are different in each Emacs job. The result is guaranteed to be a newly created empty file. On MS-DOS, this function can truncate the string prefix to fit into the 8+3 file-name limits. If prefix is a relative file name, it is expanded against
temporary-file-directory.(make-temp-file "foo") => "/tmp/foo232J6v"When
make-temp-filereturns, the file has been created and is empty. At that point, you should write the intended contents into the file.If dir-flag is non-
nil,make-temp-filecreates an empty directory instead of an empty file. It returns the file name, not the directory name, of that directory. See Directory Names.If suffix is non-
nil,make-temp-fileadds it at the end of the file name.To prevent conflicts among different libraries running in the same Emacs, each Lisp program that uses
make-temp-fileshould have its own prefix. The number added to the end of prefix distinguishes between the same application running in different Emacs jobs. Additional added characters permit a large number of distinct names even in one Emacs job.
The default directory for temporary files is controlled by the
variable temporary-file-directory. This variable gives the user
a uniform way to specify the directory for all temporary files. Some
programs use small-temporary-file-directory instead, if that is
non-nil. To use it, you should expand the prefix against
the proper directory before calling make-temp-file.
This variable specifies the directory name for creating temporary files. Its value should be a directory name (see Directory Names), but it is good for Lisp programs to cope if the value is a directory's file name instead. Using the value as the second argument to
expand-file-nameis a good way to achieve that.The default value is determined in a reasonable way for your operating system; it is based on the TMPDIR, TMP and TEMP environment variables, with a fall-back to a system-dependent name if none of these variables is defined.
Even if you do not use
make-temp-fileto create the temporary file, you should still use this variable to decide which directory to put the file in. However, if you expect the file to be small, you should usesmall-temporary-file-directoryfirst if that is non-nil.
This variable specifies the directory name for creating certain temporary files, which are likely to be small.
If you want to write a temporary file which is likely to be small, you should compute the directory like this:
(make-temp-file (expand-file-name prefix (or small-temporary-file-directory temporary-file-directory)))
This function generates a string that can be used as a unique file name. The name starts with base-name, and has several random characters appended to it, which are different in each Emacs job. It is like
make-temp-fileexcept that (i) it just constructs a name, and does not create a file, and (ii) base-name should be an absolute file name (on MS-DOS, this function can truncate base-name to fit into the 8+3 file-name limits).Warning: In most cases, you should not use this function; use
make-temp-fileinstead! This function is susceptible to a race condition, between themake-temp-namecall and the creation of the file, which in some cases may cause a security hole.
This section describes low-level subroutines for completing a file name. For higher level functions, see Reading File Names.
This function returns a list of all possible completions for a file whose name starts with partial-filename in directory directory. The order of the completions is the order of the files in the directory, which is unpredictable and conveys no useful information.
The argument partial-filename must be a file name containing no directory part and no slash (or backslash on some systems). The current buffer's default directory is prepended to directory, if directory is not absolute.
In the following example, suppose that ~rms/lewis is the current default directory, and has five files whose names begin with `f': foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-all-completions "f" "") => ("foo" "file~" "file.c.~2~" "file.c.~1~" "file.c") (file-name-all-completions "fo" "") => ("foo")
This function completes the file name filename in directory directory. It returns the longest prefix common to all file names in directory directory that start with filename. If predicate is non-
nilthen it ignores possible completions that don't satisfy predicate, after calling that function with one argument, the expanded absolute file name.If only one match exists and filename matches it exactly, the function returns
t. The function returnsnilif directory directory contains no name starting with filename.In the following example, suppose that the current default directory has five files whose names begin with `f': foo, file~, file.c, file.c.~1~, and file.c.~2~.
(file-name-completion "fi" "") => "file" (file-name-completion "file.c.~1" "") => "file.c.~1~" (file-name-completion "file.c.~1~" "") => t (file-name-completion "file.c.~3" "") => nil
file-name-completionusually ignores file names that end in any string in this list. It does not ignore them when all the possible completions end in one of these suffixes. This variable has no effect onfile-name-all-completions.A typical value might look like this:
completion-ignored-extensions => (".o" ".elc" "~" ".dvi")If an element of
completion-ignored-extensionsends in a slash `/', it signals a directory. The elements which do not end in a slash will never match a directory; thus, the above value will not filter out a directory named foo.elc.
Sometimes, an Emacs Lisp program needs to specify a standard file
name for a particular use—typically, to hold configuration data
specified by the current user. Usually, such files should be located
in the directory specified by user-emacs-directory, which is
~/.emacs.d by default (see Init File). For example, abbrev
definitions are stored by default in ~/.emacs.d/abbrev_defs.
The easiest way to specify such a file name is to use the function
locate-user-emacs-file.
This function returns an absolute file name for an Emacs-specific configuration or data file. The argument base-name should be a relative file name. The return value is the absolute name of a file in the directory specified by
user-emacs-directory; if that directory does not exist, this function creates it.If the optional argument old-name is non-
nil, it specifies a file in the user's home directory, ~/old-name. If such a file exists, the return value is the absolute name of that file, instead of the file specified by base-name. This argument is intended to be used by Emacs packages to provide backward compatibility. For instance, prior to the introduction ofuser-emacs-directory, the abbrev file was located in ~/.abbrev_defs. Here is the definition ofabbrev-file-name:(defcustom abbrev-file-name (locate-user-emacs-file "abbrev_defs" ".abbrev_defs") "Default name of file from which to read abbrevs." ... :type 'file)
A lower-level function for standardizing file names, which
locate-user-emacs-file uses as a subroutine, is
convert-standard-filename.
This function returns a file name based on filename, which fits the conventions of the current operating system.
On GNU and Unix systems, this simply returns filename. On other operating systems, it may enforce system-specific file name conventions; for example, on MS-DOS this function performs a variety of changes to enforce MS-DOS file name limitations, including converting any leading `.' to `_' and truncating to three characters after the `.'.
The recommended way to use this function is to specify a name which fits the conventions of GNU and Unix systems, and pass it to
convert-standard-filename.
A directory is a kind of file that contains other files entered under various names. Directories are a feature of the file system.
Emacs can list the names of the files in a directory as a Lisp list,
or display the names in a buffer using the ls shell command. In
the latter case, it can optionally display information about each file,
depending on the options passed to the ls command.
This function returns a list of the names of the files in the directory directory. By default, the list is in alphabetical order.
If full-name is non-
nil, the function returns the files' absolute file names. Otherwise, it returns the names relative to the specified directory.If match-regexp is non-
nil, this function returns only those file names that contain a match for that regular expression—the other file names are excluded from the list. On case-insensitive filesystems, the regular expression matching is case-insensitive.If nosort is non-
nil,directory-filesdoes not sort the list, so you get the file names in no particular order. Use this if you want the utmost possible speed and don't care what order the files are processed in. If the order of processing is visible to the user, then the user will probably be happier if you do sort the names.(directory-files "~lewis") => ("#foo#" "#foo.el#" "." ".." "dired-mods.el" "files.texi" "files.texi.~1~")An error is signaled if directory is not the name of a directory that can be read.
Return all files under directory whose names match regexp. This function searches the specified directory and its sub-directories, recursively, for files whose basenames (i.e., without the leading directories) match the specified regexp, and returns a list of the absolute file names of the matching files (see absolute file names). The file names are returned in depth-first order, meaning that files in some sub-directory are returned before the files in its parent directory. In addition, matching files found in each subdirectory are sorted alphabetically by their basenames. By default, directories whose names match regexp are omitted from the list, but if the optional argument include-directories is non-
nil, they are included.
This is similar to
directory-filesin deciding which files to report on and how to report their names. However, instead of returning a list of file names, it returns for each file a list(filename.attributes), where attributes is whatfile-attributeswould return for that file. The optional argument id-format has the same meaning as the corresponding argument tofile-attributes(see Definition of file-attributes).
This function expands the wildcard pattern pattern, returning a list of file names that match it.
If pattern is written as an absolute file name, the values are absolute also.
If pattern is written as a relative file name, it is interpreted relative to the current default directory. The file names returned are normally also relative to the current default directory. However, if full is non-
nil, they are absolute.
This function inserts (in the current buffer) a directory listing for directory file, formatted with
lsaccording to switches. It leaves point after the inserted text. switches may be a string of options, or a list of strings representing individual options.The argument file may be either a directory name or a file specification including wildcard characters. If wildcard is non-
nil, that means treat file as a file specification with wildcards.If full-directory-p is non-
nil, that means the directory listing is expected to show the full contents of a directory. You should specifytwhen file is a directory and switches do not contain `-d'. (The `-d' option tolssays to describe a directory itself as a file, rather than showing its contents.)On most systems, this function works by running a directory listing program whose name is in the variable
insert-directory-program. If wildcard is non-nil, it also runs the shell specified byshell-file-name, to expand the wildcards.MS-DOS and MS-Windows systems usually lack the standard Unix program
ls, so this function emulates the standard Unix programlswith Lisp code.As a technical detail, when switches contains the long `--dired' option,
insert-directorytreats it specially, for the sake of dired. However, the normally equivalent short `-D' option is just passed on toinsert-directory-program, as any other option.
This variable's value is the program to run to generate a directory listing for the function
insert-directory. It is ignored on systems which generate the listing with Lisp code.
Most Emacs Lisp file-manipulation functions get errors when used on
files that are directories. For example, you cannot delete a directory
with delete-file. These special functions exist to create and
delete directories.
This command creates a directory named dirname. If parents is non-
nil, as is always the case in an interactive call, that means to create the parent directories first, if they don't already exist.
mkdiris an alias for this.
This command copies the directory named dirname to newname. If newname names an existing directory, dirname will be copied to a subdirectory there.
It always sets the file modes of the copied files to match the corresponding original file.
The third argument keep-time non-
nilmeans to preserve the modification time of the copied files. A prefix arg makes keep-time non-nil.The fourth argument parents says whether to create parent directories if they don't exist. Interactively, this happens by default.
The fifth argument copy-contents, if non-
nil, means to copy the contents of dirname directly into newname if the latter is an existing directory, instead of copying dirname into it as a subdirectory.
This command deletes the directory named dirname. The function
delete-filedoes not work for files that are directories; you must usedelete-directoryfor them. If recursive isnil, and the directory contains any files,delete-directorysignals an error.
delete-directoryonly follows symbolic links at the level of parent directories.If the optional argument trash is non-
niland the variabledelete-by-moving-to-trashis non-nil, this command moves the file into the system Trash instead of deleting it. See Miscellaneous File Operations. When called interactively, trash istif no prefix argument is given, andnilotherwise.
You can implement special handling for certain file names. This is called making those names magic. The principal use for this feature is in implementing access to remote files (see Remote Files).
To define a kind of magic file name, you must supply a regular expression to define the class of names (all those that match the regular expression), plus a handler that implements all the primitive Emacs file operations for file names that match.
The variable file-name-handler-alist holds a list of handlers,
together with regular expressions that determine when to apply each
handler. Each element has this form:
(regexp . handler)
All the Emacs primitives for file access and file name transformation
check the given file name against file-name-handler-alist. If
the file name matches regexp, the primitives handle that file by
calling handler.
The first argument given to handler is the name of the primitive, as a symbol; the remaining arguments are the arguments that were passed to that primitive. (The first of these arguments is most often the file name itself.) For example, if you do this:
(file-exists-p filename)
and filename has handler handler, then handler is called like this:
(funcall handler 'file-exists-p filename)
When a function takes two or more arguments that must be file names, it checks each of those names for a handler. For example, if you do this:
(expand-file-name filename dirname)
then it checks for a handler for filename and then for a handler for dirname. In either case, the handler is called like this:
(funcall handler 'expand-file-name filename dirname)
The handler then needs to figure out whether to handle filename or dirname.
If the specified file name matches more than one handler, the one whose match starts last in the file name gets precedence. This rule is chosen so that handlers for jobs such as uncompression are handled first, before handlers for jobs such as remote file access.
Here are the operations that a magic file name handler gets to handle:
access-file, add-name-to-file,
byte-compiler-base-file-name,
copy-directory, copy-file,
delete-directory, delete-file,
diff-latest-backup-file,
directory-file-name,
directory-files,
directory-files-and-attributes,
dired-compress-file, dired-uncache,
expand-file-name,
file-accessible-directory-p,
file-acl,
file-attributes,
file-directory-p,
file-equal-p,
file-executable-p, file-exists-p,
file-in-directory-p,
file-local-copy,
file-modes, file-name-all-completions,
file-name-as-directory,
file-name-completion,
file-name-directory,
file-name-nondirectory,
file-name-sans-versions, file-newer-than-file-p,
file-notify-add-watch, file-notify-rm-watch,
file-notify-valid-p,
file-ownership-preserved-p,
file-readable-p, file-regular-p,
file-remote-p, file-selinux-context,
file-symlink-p, file-truename, file-writable-p,
find-backup-file-name,
get-file-buffer,
insert-directory,
insert-file-contents,
load,
make-auto-save-file-name,
make-directory,
make-directory-internal,
make-symbolic-link,
process-file,
rename-file, set-file-acl, set-file-modes,
set-file-selinux-context, set-file-times,
set-visited-file-modtime, shell-command,
start-file-process,
substitute-in-file-name,
unhandled-file-name-directory,
vc-registered,
verify-visited-file-modtime,
write-region.
Handlers for insert-file-contents typically need to clear the
buffer's modified flag, with (set-buffer-modified-p nil), if the
visit argument is non-nil. This also has the effect of
unlocking the buffer if it is locked.
The handler function must handle all of the above operations, and possibly others to be added in the future. It need not implement all these operations itself—when it has nothing special to do for a certain operation, it can reinvoke the primitive, to handle the operation in the usual way. It should always reinvoke the primitive for an operation it does not recognize. Here's one way to do this:
(defun my-file-handler (operation &rest args)
;; First check for the specific operations
;; that we have special handling for.
(cond ((eq operation 'insert-file-contents) ...)
((eq operation 'write-region) ...)
...
;; Handle any operation we don't know about.
(t (let ((inhibit-file-name-handlers
(cons 'my-file-handler
(and (eq inhibit-file-name-operation operation)
inhibit-file-name-handlers)))
(inhibit-file-name-operation operation))
(apply operation args)))))
When a handler function decides to call the ordinary Emacs primitive for
the operation at hand, it needs to prevent the primitive from calling
the same handler once again, thus leading to an infinite recursion. The
example above shows how to do this, with the variables
inhibit-file-name-handlers and
inhibit-file-name-operation. Be careful to use them exactly as
shown above; the details are crucial for proper behavior in the case of
multiple handlers, and for operations that have two file names that may
each have handlers.
Handlers that don't really do anything special for actual access to the
file—such as the ones that implement completion of host names for
remote file names—should have a non-nil safe-magic
property. For instance, Emacs normally protects directory names
it finds in PATH from becoming magic, if they look like magic
file names, by prefixing them with `/:'. But if the handler that
would be used for them has a non-nil safe-magic
property, the `/:' is not added.
A file name handler can have an operations property to
declare which operations it handles in a nontrivial way. If this
property has a non-nil value, it should be a list of
operations; then only those operations will call the handler. This
avoids inefficiency, but its main purpose is for autoloaded handler
functions, so that they won't be loaded except when they have real
work to do.
Simply deferring all operations to the usual primitives does not
work. For instance, if the file name handler applies to
file-exists-p, then it must handle load itself, because
the usual load code won't work properly in that case. However,
if the handler uses the operations property to say it doesn't
handle file-exists-p, then it need not handle load
nontrivially.
This variable holds a list of handlers whose use is presently inhibited for a certain operation.
The operation for which certain handlers are presently inhibited.
This function returns the handler function for file name file, or
nilif there is none. The argument operation should be the operation to be performed on the file—the value you will pass to the handler as its first argument when you call it. If operation equalsinhibit-file-name-operation, or if it is not found in theoperationsproperty of the handler, this function returnsnil.
This function copies file filename to an ordinary non-magic file on the local machine, if it isn't on the local machine already. Magic file names should handle the
file-local-copyoperation if they refer to files on other machines. A magic file name that is used for other purposes than remote file access should not handlefile-local-copy; then this function will treat the file as local.If filename is local, whether magic or not, this function does nothing and returns
nil. Otherwise it returns the file name of the local copy file.
This function tests whether filename is a remote file. If filename is local (not remote), the return value is
nil. If filename is indeed remote, the return value is a string that identifies the remote system.This identifier string can include a host name and a user name, as well as characters designating the method used to access the remote system. For example, the remote identifier string for the filename
/sudo::/some/fileis/sudo:root@localhost:.If
file-remote-preturns the same identifier for two different filenames, that means they are stored on the same file system and can be accessed locally with respect to each other. This means, for example, that it is possible to start a remote process accessing both files at the same time. Implementers of file handlers need to ensure this principle is valid.identification specifies which part of the identifier shall be returned as string. identification can be the symbol
method,userorhost; any other value is handled likeniland means to return the complete identifier string. In the example above, the remoteuseridentifier string would beroot.If connected is non-
nil, this function returnsnileven if filename is remote, if Emacs has no network connection to its host. This is useful when you want to avoid the delay of making connections when they don't exist.
This function returns the name of a directory that is not magic. For a non-magic filename it returns the corresponding directory name (see Directory Names). For a magic filename, it invokes the file name handler, which therefore decides what value to return. If filename is not accessible from a local process, then the file name handler should indicate that by returning
nil.This is useful for running a subprocess; every subprocess must have a non-magic directory to serve as its current directory, and this function is a good way to come up with one.
The attributes of remote files can be cached for better performance. If they are changed outside of Emacs's control, the cached values become invalid, and must be reread.
When this variable is set to
nil, cached values are never expired. Use this setting with caution, only if you are sure nothing other than Emacs ever changes the remote files. If it is set tot, cached values are never used. This is the safest value, but could result in performance degradation.A compromise is to set it to a positive number. This means that cached values are used for that amount of seconds since they were cached. If a remote file is checked regularly, it might be a good idea to let-bind this variable to a value less than the time period between consecutive checks. For example:
(defun display-time-file-nonempty-p (file) (let ((remote-file-name-inhibit-cache (- display-time-interval 5))) (and (file-exists-p file) (< 0 (nth 7 (file-attributes (file-chase-links file)))))))
Emacs performs several steps to convert the data in a buffer (text,
text properties, and possibly other information) to and from a
representation suitable for storing into a file. This section describes
the fundamental functions that perform this format conversion,
namely insert-file-contents for reading a file into a buffer,
and write-region for writing a buffer into a file.
The function insert-file-contents:
format-alist; and
after-insert-file-functions.
The function write-region:
write-region-annotate-functions;
format-alist;
This shows the symmetry of the lowest-level operations; reading and writing handle things in opposite order. The rest of this section describes the two facilities surrounding the three variables named above, as well as some related functions. Coding Systems, for details on character encoding and decoding.
The most general of the two facilities is controlled by the variable
format-alist, a list of file format specifications, which
describe textual representations used in files for the data in an Emacs
buffer. The descriptions for reading and writing are paired, which is
why we call this “round-trip” specification
(see Format Conversion Piecemeal, for non-paired specification).
This list contains one format definition for each defined file format. Each format definition is a list of this form:
(name doc-string regexp from-fn to-fn modify mode-fn preserve)
Here is what the elements in a format definition mean:
nil, the format is never applied automatically.
A shell command is represented as a string; Emacs runs the command as a filter to perform the conversion.
If from-fn is a function, it is called with two arguments, begin and end, which specify the part of the buffer it should convert. It should convert the text by editing it in place. Since this can change the length of the text, from-fn should return the modified end position.
One responsibility of from-fn is to make sure that the beginning
of the file no longer matches regexp. Otherwise it is likely to
get called again.
If to-fn is a string, it is a shell command; Emacs runs the command as a filter to perform the conversion.
If to-fn is a function, it is called with three arguments: begin and end, which specify the part of the buffer it should convert, and buffer, which specifies which buffer. There are two ways it can do the conversion:
(position . string), where position is an
integer specifying the relative position in the text to be written, and
string is the annotation to add there. The list must be sorted in
order of position when to-fn returns it.
When write-region actually writes the text from the buffer to the
file, it intermixes the specified annotations at the corresponding
positions. All this takes place without modifying the buffer.
t if the encoding function modifies the buffer, and
nil if it works by returning a list of annotations.
t if format-write-file should not remove this format
from buffer-file-format.
The function insert-file-contents automatically recognizes file
formats when it reads the specified file. It checks the text of the
beginning of the file against the regular expressions of the format
definitions, and if it finds a match, it calls the decoding function for
that format. Then it checks all the known formats over again.
It keeps checking them until none of them is applicable.
Visiting a file, with find-file-noselect or the commands that use
it, performs conversion likewise (because it calls
insert-file-contents); it also calls the mode function for each
format that it decodes. It stores a list of the format names in the
buffer-local variable buffer-file-format.
This variable states the format of the visited file. More precisely, this is a list of the file format names that were decoded in the course of visiting the current buffer's file. It is always buffer-local in all buffers.
When write-region writes data into a file, it first calls the
encoding functions for the formats listed in buffer-file-format,
in the order of appearance in the list.
This command writes the current buffer contents into the file file in a format based on format, which is a list of format names. It constructs the actual format starting from format, then appending any elements from the value of
buffer-file-formatwith a non-nilpreserve flag (see above), if they are not already present in format. It then updatesbuffer-file-formatwith this format, making it the default for future saves. Except for the format argument, this command is similar towrite-file. In particular, confirm has the same meaning and interactive treatment as the corresponding argument towrite-file. See Definition of write-file.
This command finds the file file, converting it according to format format. It also makes format the default if the buffer is saved later.
The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just <RET> for format specifiesnil.
This command inserts the contents of file file, converting it according to format format. If beg and end are non-
nil, they specify which part of the file to read, as ininsert-file-contents(see Reading from Files).The return value is like what
insert-file-contentsreturns: a list of the absolute file name and the length of the data inserted (after conversion).The argument format is a list of format names. If format is
nil, no conversion takes place. Interactively, typing just <RET> for format specifiesnil.
This variable specifies the format to use for auto-saving. Its value is a list of format names, just like the value of
buffer-file-format; however, it is used instead ofbuffer-file-formatfor writing auto-save files. If the value ist, the default, auto-saving uses the same format as a regular save in the same buffer. This variable is always buffer-local in all buffers.
In contrast to the round-trip specification described in the previous
subsection (see Format Conversion Round-Trip), you can use the variables
after-insert-file-functions and write-region-annotate-functions
to separately control the respective reading and writing conversions.
Conversion starts with one representation and produces another representation. When there is only one conversion to do, there is no conflict about what to start with. However, when there are multiple conversions involved, conflict may arise when two conversions need to start with the same data.
This situation is best understood in the context of converting text
properties during write-region. For example, the character at
position 42 in a buffer is `X' with a text property foo. If
the conversion for foo is done by inserting into the buffer, say,
`FOO:', then that changes the character at position 42 from
`X' to `F'. The next conversion will start with the wrong
data straight away.
To avoid conflict, cooperative conversions do not modify the buffer,
but instead specify annotations, a list of elements of the form
(position . string), sorted in order of increasing
position.
If there is more than one conversion, write-region merges their
annotations destructively into one sorted list. Later, when the text
from the buffer is actually written to the file, it intermixes the
specified annotations at the corresponding positions. All this takes
place without modifying the buffer.
In contrast, when reading, the annotations intermixed with the text
are handled immediately. insert-file-contents sets point to
the beginning of some text to be converted, then calls the conversion
functions with the length of that text. These functions should always
return with point at the beginning of the inserted text. This
approach makes sense for reading because annotations removed by the
first converter can't be mistakenly processed by a later converter.
Each conversion function should scan for the annotations it
recognizes, remove the annotation, modify the buffer text (to set a
text property, for example), and return the updated length of the
text, as it stands after those changes. The value returned by one
function becomes the argument to the next function.
A list of functions for
write-regionto call. Each function in the list is called with two arguments: the start and end of the region to be written. These functions should not alter the contents of the buffer. Instead, they should return annotations.As a special case, a function may return with a different buffer current. Emacs takes this to mean that the current buffer contains altered text to be output. It therefore changes the start and end arguments of the
write-regioncall, giving them the values ofpoint-minandpoint-maxin the new buffer, respectively. It also discards all previous annotations, because they should have been dealt with by this function.
The value of this variable, if non-
nil, should be a function. This function is called, with no arguments, afterwrite-regionhas completed.If any function in
write-region-annotate-functionsreturns with a different buffer current, Emacs callswrite-region-post-annotation-functionmore than once. Emacs calls it with the last buffer that was current, and again with the buffer before that, and so on back to the original buffer.Thus, a function in
write-region-annotate-functionscan create a buffer, give this variable the local value ofkill-bufferin that buffer, set up the buffer with altered text, and make the buffer current. The buffer will be killed afterwrite-regionis done.
Each function in this list is called by
insert-file-contentswith one argument, the number of characters inserted, and with point at the beginning of the inserted text. Each function should leave point unchanged, and return the new character count describing the inserted text as modified by the function.
We invite users to write Lisp programs to store and retrieve text properties in files, using these hooks, and thus to experiment with various data formats and find good ones. Eventually we hope users will produce good, general extensions we can install in Emacs.
We suggest not trying to handle arbitrary Lisp objects as text property names or values—because a program that general is probably difficult to write, and slow. Instead, choose a set of possible data types that are reasonably flexible, and not too hard to encode.
Backup files and auto-save files are two methods by which Emacs tries to protect the user from the consequences of crashes or of the user's own errors. Auto-saving preserves the text from earlier in the current editing session; backup files preserve file contents prior to the current session.
A backup file is a copy of the old contents of a file you are editing. Emacs makes a backup file the first time you save a buffer into its visited file. Thus, normally, the backup file contains the contents of the file as it was before the current editing session. The contents of the backup file normally remain unchanged once it exists.
Backups are usually made by renaming the visited file to a new name. Optionally, you can specify that backup files should be made by copying the visited file. This choice makes a difference for files with multiple names; it also can affect whether the edited file remains owned by the original owner or becomes owned by the user editing it.
By default, Emacs makes a single backup file for each file edited. You can alternatively request numbered backups; then each new backup file gets a new name. You can delete old numbered backups when you don't want them any more, or Emacs can delete them automatically.
This function makes a backup of the file visited by the current buffer, if appropriate. It is called by
save-bufferbefore saving the buffer the first time.If a backup was made by renaming, the return value is a cons cell of the form (modes extra-alist backupname), where modes are the mode bits of the original file, as returned by
file-modes(see Testing Accessibility), extra-alist is an alist describing the original file's extended attributes, as returned byfile-extended-attributes(see Extended Attributes), and backupname is the name of the backup.In all other cases (i.e., if a backup was made by copying or if no backup was made), this function returns
nil.
This buffer-local variable says whether this buffer's file has been backed up on account of this buffer. If it is non-
nil, the backup file has been written. Otherwise, the file should be backed up when it is next saved (if backups are enabled). This is a permanent local;kill-all-local-variablesdoes not alter it.
This variable determines whether or not to make backup files. If it is non-
nil, then Emacs creates a backup of each file when it is saved for the first time—provided thatbackup-inhibitedisnil(see below).The following example shows how to change the
make-backup-filesvariable only in the Rmail buffers and not elsewhere. Setting itnilstops Emacs from making backups of these files, which may save disk space. (You would put this code in your init file.)(add-hook 'rmail-mode-hook (lambda () (setq-local make-backup-files nil)))
This variable's value is a function to be called on certain occasions to decide whether a file should have backup files. The function receives one argument, an absolute file name to consider. If the function returns
nil, backups are disabled for that file. Otherwise, the other variables in this section say whether and how to make backups.The default value is
normal-backup-enable-predicate, which checks for files intemporary-file-directoryandsmall-temporary-file-directory.
If this variable is non-
nil, backups are inhibited. It records the result of testingbackup-enable-predicateon the visited file name. It can also coherently be used by other mechanisms that inhibit backups based on which file is visited. For example, VC sets this variable non-nilto prevent making backups for files managed with a version control system.This is a permanent local, so that changing the major mode does not lose its value. Major modes should not set this variable—they should set
make-backup-filesinstead.
This variable's value is an alist of filename patterns and backup directory names. Each element looks like
(regexp . directory)Backups of files with names matching regexp will be made in directory. directory may be relative or absolute. If it is absolute, so that all matching files are backed up into the same directory, the file names in this directory will be the full name of the file backed up with all directory separators changed to `!' to prevent clashes. This will not work correctly if your filesystem truncates the resulting name.
For the common case of all backups going into one directory, the alist should contain a single element pairing `"."' with the appropriate directory name.
If this variable is
nil(the default), or it fails to match a filename, the backup is made in the original file's directory.On MS-DOS filesystems without long names this variable is always ignored.
This variable's value is a function to use for making backup file names. The function
make-backup-file-namecalls it. See Naming Backup Files.This could be buffer-local to do something special for specific files. If you change it, you may need to change
backup-file-name-pandfile-name-sans-versionstoo.
There are two ways that Emacs can make a backup file:
The first method, renaming, is the default.
The variable backup-by-copying, if non-nil, says to use
the second method, which is to copy the original file and overwrite it
with the new buffer contents. The variable file-precious-flag,
if non-nil, also has this effect (as a sideline of its main
significance). See Saving Buffers.
If this variable is non-
nil, Emacs always makes backup files by copying. The default isnil.
The following three variables, when non-nil, cause the second
method to be used in certain special cases. They have no effect on the
treatment of files that don't fall into the special cases.
If this variable is non-
nil, Emacs makes backups by copying for files with multiple names (hard links). The default isnil.This variable is significant only if
backup-by-copyingisnil, since copying is always used when that variable is non-nil.
If this variable is non-
nil(the default), Emacs makes backups by copying in cases where renaming would change either the owner or the group of the file.The value has no effect when renaming would not alter the owner or group of the file; that is, for files which are owned by the user and whose group matches the default for a new file created there by the user.
This variable is significant only if
backup-by-copyingisnil, since copying is always used when that variable is non-nil.
This variable, if non-
nil, specifies the same behavior asbackup-by-copying-when-mismatch, but only for certain user-id values: namely, those less than or equal to a certain number. You set this variable to that number.Thus, if you set
backup-by-copying-when-privileged-mismatchto 0, backup by copying is done for the superuser only, when necessary to prevent a change in the owner of the file.The default is 200.
If a file's name is foo, the names of its numbered backup versions are foo.~v~, for various integers v, like this: foo.~1~, foo.~2~, foo.~3~, ..., foo.~259~, and so on.
This variable controls whether to make a single non-numbered backup file or multiple numbered backups.
nil- Make numbered backups if the visited file already has numbered backups; otherwise, do not. This is the default.
never- Do not make numbered backups.
- anything else
- Make numbered backups.
The use of numbered backups ultimately leads to a large number of backup versions, which must then be deleted. Emacs can do this automatically or it can ask the user whether to delete them.
The value of this variable is the number of newest versions to keep when a new numbered backup is made. The newly made backup is included in the count. The default value is 2.
The value of this variable is the number of oldest versions to keep when a new numbered backup is made. The default value is 2.
If there are backups numbered 1, 2, 3, 5, and 7, and both of these
variables have the value 2, then the backups numbered 1 and 2 are kept
as old versions and those numbered 5 and 7 are kept as new versions;
backup version 3 is excess. The function find-backup-file-name
(see Backup Names) is responsible for determining which backup
versions to delete, but does not delete them itself.
If this variable is
t, then saving a file deletes excess backup versions silently. If it isnil, that means to ask for confirmation before deleting excess backups. Otherwise, they are not deleted at all.
This variable specifies how many of the newest backup versions to keep in the Dired command . (
dired-clean-directory). That's the same thingkept-new-versionsspecifies when you make a new backup file. The default is 2.
The functions in this section are documented mainly because you can customize the naming conventions for backup files by redefining them. If you change one, you probably need to change the rest.
This function returns a non-
nilvalue if filename is a possible name for a backup file. It just checks the name, not whether a file with the name filename exists.(backup-file-name-p "foo") => nil (backup-file-name-p "foo~") => 3The standard definition of this function is as follows:
(defun backup-file-name-p (file) "Return non-nil if FILE is a backup file \ name (numeric or not)..." (string-match "~\\'" file))Thus, the function returns a non-
nilvalue if the file name ends with a `~'. (We use a backslash to split the documentation string's first line into two lines in the text, but produce just one line in the string itself.)This simple expression is placed in a separate function to make it easy to redefine for customization.
This function returns a string that is the name to use for a non-numbered backup file for file filename. On Unix, this is just filename with a tilde appended.
The standard definition of this function, on most operating systems, is as follows:
(defun make-backup-file-name (file) "Create the non-numeric backup file name for FILE..." (concat file "~"))You can change the backup-file naming convention by redefining this function. The following example redefines
make-backup-file-nameto prepend a `.' in addition to appending a tilde:(defun make-backup-file-name (filename) (expand-file-name (concat "." (file-name-nondirectory filename) "~") (file-name-directory filename))) (make-backup-file-name "backups.texi") => ".backups.texi~"Some parts of Emacs, including some Dired commands, assume that backup file names end with `~'. If you do not follow that convention, it will not cause serious problems, but these commands may give less-than-desirable results.
This function computes the file name for a new backup file for filename. It may also propose certain existing backup files for deletion.
find-backup-file-namereturns a list whose car is the name for the new backup file and whose cdr is a list of backup files whose deletion is proposed. The value can also benil, which means not to make a backup.Two variables,
kept-old-versionsandkept-new-versions, determine which backup versions should be kept. This function keeps those versions by excluding them from the cdr of the value. See Numbered Backups.In this example, the value says that ~rms/foo.~5~ is the name to use for the new backup file, and ~rms/foo.~3~ is an excess version that the caller should consider deleting now.
(find-backup-file-name "~rms/foo") => ("~rms/foo.~5~" "~rms/foo.~3~")
This function returns the name of the most recent backup file for filename, or
nilif that file has no backup files.Some file comparison commands use this function so that they can automatically compare a file with its most recent backup.
Emacs periodically saves all files that you are visiting; this is called auto-saving. Auto-saving prevents you from losing more than a limited amount of work if the system crashes. By default, auto-saves happen every 300 keystrokes, or after around 30 seconds of idle time. See Auto Save, for information on auto-save for users. Here we describe the functions used to implement auto-saving and the variables that control them.
This buffer-local variable is the name of the file used for auto-saving the current buffer. It is
nilif the buffer should not be auto-saved.buffer-auto-save-file-name => "/xcssun/users/rms/lewis/#backups.texi#"
This is the mode command for Auto Save mode, a buffer-local minor mode. When Auto Save mode is enabled, auto-saving is enabled in the buffer. The calling convention is the same as for other minor mode commands (see Minor Mode Conventions).
Unlike most minor modes, there is no
auto-save-modevariable. Auto Save mode is enabled ifbuffer-auto-save-file-nameis non-nilandbuffer-saved-size(see below) is non-zero.
This function returns a non-
nilvalue if filename is a string that could be the name of an auto-save file. It assumes the usual naming convention for auto-save files: a name that begins and ends with hash marks (`#') is a possible auto-save file name. The argument filename should not contain a directory part.(make-auto-save-file-name) => "/xcssun/users/rms/lewis/#backups.texi#" (auto-save-file-name-p "#backups.texi#") => 0 (auto-save-file-name-p "backups.texi") => nilThe standard definition of this function is as follows:
(defun auto-save-file-name-p (filename) "Return non-nil if FILENAME can be yielded by..." (string-match "^#.*#$" filename))This function exists so that you can customize it if you wish to change the naming convention for auto-save files. If you redefine it, be sure to redefine the function
make-auto-save-file-namecorrespondingly.
This function returns the file name to use for auto-saving the current buffer. This is just the file name with hash marks (`#') prepended and appended to it. This function does not look at the variable
auto-save-visited-file-name(described below); callers of this function should check that variable first.(make-auto-save-file-name) => "/xcssun/users/rms/lewis/#backups.texi#"Here is a simplified version of the standard definition of this function:
(defun make-auto-save-file-name () "Return file name to use for auto-saves \ of current buffer.." (if buffer-file-name (concat (file-name-directory buffer-file-name) "#" (file-name-nondirectory buffer-file-name) "#") (expand-file-name (concat "#%" (buffer-name) "#"))))This exists as a separate function so that you can redefine it to customize the naming convention for auto-save files. Be sure to change
auto-save-file-name-pin a corresponding way.
If this variable is non-
nil, Emacs auto-saves buffers in the files they are visiting. That is, the auto-save is done in the same file that you are editing. Normally, this variable isnil, so auto-save files have distinct names that are created bymake-auto-save-file-name.When you change the value of this variable, the new value does not take effect in an existing buffer until the next time auto-save mode is reenabled in it. If auto-save mode is already enabled, auto-saves continue to go in the same file name until
auto-save-modeis called again.
This function returns
tif the current buffer has been auto-saved since the last time it was read in or saved.
This function marks the current buffer as auto-saved. The buffer will not be auto-saved again until the buffer text is changed again. The function returns
nil.
The value of this variable specifies how often to do auto-saving, in terms of number of input events. Each time this many additional input events are read, Emacs does auto-saving for all buffers in which that is enabled. Setting this to zero disables autosaving based on the number of characters typed.
The value of this variable is the number of seconds of idle time that should cause auto-saving. Each time the user pauses for this long, Emacs does auto-saving for all buffers in which that is enabled. (If the current buffer is large, the specified timeout is multiplied by a factor that increases as the size increases; for a million-byte buffer, the factor is almost 4.)
If the value is zero or
nil, then auto-saving is not done as a result of idleness, only after a certain number of input events as specified byauto-save-interval.
If this variable is non-
nil, buffers that are visiting files have auto-saving enabled by default. Otherwise, they do not.
This function auto-saves all buffers that need to be auto-saved. It saves all buffers for which auto-saving is enabled and that have been changed since the previous auto-save.
If any buffers are auto-saved,
do-auto-savenormally displays a message saying `Auto-saving...' in the echo area while auto-saving is going on. However, if no-message is non-nil, the message is inhibited.If current-only is non-
nil, only the current buffer is auto-saved.
This function deletes the current buffer's auto-save file if
delete-auto-save-filesis non-nil. It is called every time a buffer is saved.Unless force is non-
nil, this function only deletes the file if it was written by the current Emacs session since the last true save.
This variable is used by the function
delete-auto-save-file-if-necessary. If it is non-nil, Emacs deletes auto-save files when a true save is done (in the visited file). This saves disk space and unclutters your directory.
This function adjusts the current buffer's auto-save file name if the visited file name has changed. It also renames an existing auto-save file, if it was made in the current Emacs session. If the visited file name has not changed, this function does nothing.
The value of this buffer-local variable is the length of the current buffer, when it was last read in, saved, or auto-saved. This is used to detect a substantial decrease in size, and turn off auto-saving in response.
If it is −1, that means auto-saving is temporarily shut off in this buffer due to a substantial decrease in size. Explicitly saving the buffer stores a positive value in this variable, thus reenabling auto-saving. Turning auto-save mode off or on also updates this variable, so that the substantial decrease in size is forgotten.
If it is −2, that means this buffer should disregard changes in buffer size; in particular, it should not shut off auto-saving temporarily due to changes in buffer size.
This variable (if non-
nil) specifies a file for recording the names of all the auto-save files. Each time Emacs does auto-saving, it writes two lines into this file for each buffer that has auto-saving enabled. The first line gives the name of the visited file (it's empty if the buffer has none), and the second gives the name of the auto-save file.When Emacs exits normally, it deletes this file; if Emacs crashes, you can look in the file to find all the auto-save files that might contain work that was otherwise lost. The
recover-sessioncommand uses this file to find them.The default name for this file specifies your home directory and starts with `.saves-'. It also contains the Emacs process ID and the host name.
After Emacs reads your init file, it initializes
auto-save-list-file-name(if you have not already set it non-nil) based on this prefix, adding the host name and process ID. If you set this tonilin your init file, then Emacs does not initializeauto-save-list-file-name.
If you have made extensive changes to a file and then change your mind
about them, you can get rid of them by reading in the previous version
of the file with the revert-buffer command. See Reverting a Buffer.
This command replaces the buffer text with the text of the visited file on disk. This action undoes all changes since the file was visited or saved.
By default, if the latest auto-save file is more recent than the visited file, and the argument ignore-auto is
nil,revert-bufferasks the user whether to use that auto-save instead. When you invoke this command interactively, ignore-auto istif there is no numeric prefix argument; thus, the interactive default is not to check the auto-save file.Normally,
revert-bufferasks for confirmation before it changes the buffer; but if the argument noconfirm is non-nil,revert-bufferdoes not ask for confirmation.Normally, this command reinitializes the buffer's major and minor modes using
normal-mode. But if preserve-modes is non-nil, the modes remain unchanged.Reverting tries to preserve marker positions in the buffer by using the replacement feature of
insert-file-contents. If the buffer contents and the file contents are identical before the revert operation, reverting preserves all the markers. If they are not identical, reverting does change the buffer; in that case, it preserves the markers in the unchanged text (if any) at the beginning and end of the buffer. Preserving any additional markers would be problematical.
revert-bufferbinds this variable to a non-nilvalue while it is working.
You can customize how revert-buffer does its work by setting
the variables described in the rest of this section.
This variable holds a list of files that should be reverted without query. The value is a list of regular expressions. If the visited file name matches one of these regular expressions, and the file has changed on disk but the buffer is not modified, then
revert-bufferreverts the file without asking the user for confirmation.
Some major modes customize revert-buffer by making
buffer-local bindings for these variables:
The value of this variable is the function to use to revert this buffer. It should be a function with two optional arguments to do the work of reverting. The two optional arguments, ignore-auto and noconfirm, are the arguments that
revert-bufferreceived.Modes such as Dired mode, in which the text being edited does not consist of a file's contents but can be regenerated in some other fashion, can give this variable a buffer-local value that is a special function to regenerate the contents.
The value of this variable specifies the function to use to insert the updated contents when reverting this buffer. The function receives two arguments: first the file name to use; second,
tif the user has asked to read the auto-save file.The reason for a mode to change this variable instead of
revert-buffer-functionis to avoid duplicating or replacing the rest of whatrevert-bufferdoes: asking for confirmation, clearing the undo list, deciding the proper major mode, and running the hooks listed below.
This normal hook is run by the default
revert-buffer-functionbefore inserting the modified contents. A customrevert-buffer-functionmay or may not run this hook.
This normal hook is run by the default
revert-buffer-functionafter inserting the modified contents. A customrevert-buffer-functionmay or may not run this hook.
The value of this variable specifies a function to call to check whether a buffer needs reverting. The default value only handles buffers that are visiting files, by checking their modification time. Buffers that are not visiting files require a custom function (see Supporting additional buffers).
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. While several buffers may exist at one time, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
A buffer is a Lisp object containing text to be edited. Buffers are used to hold the contents of files that are being visited; there may also be buffers that are not visiting files. Although several buffers normally exist, only one buffer is designated the current buffer at any time. Most editing commands act on the contents of the current buffer. Each buffer, including the current buffer, may or may not be displayed in any windows.
Buffers in Emacs editing are objects that have distinct names and hold text that can be edited. Buffers appear to Lisp programs as a special data type. You can think of the contents of a buffer as a string that you can extend; insertions and deletions may occur in any part of the buffer. See Text.
A Lisp buffer object contains numerous pieces of information. Some of this information is directly accessible to the programmer through variables, while other information is accessible only through special-purpose functions. For example, the visited file name is directly accessible through a variable, while the value of point is accessible only through a primitive function.
Buffer-specific information that is directly accessible is stored in
buffer-local variable bindings, which are variable values that are
effective only in a particular buffer. This feature allows each buffer
to override the values of certain variables. Most major modes override
variables such as fill-column or comment-column in this
way. For more information about buffer-local variables and functions
related to them, see Buffer-Local Variables.
For functions and variables related to visiting files in buffers, see Visiting Files and Saving Buffers. For functions and variables related to the display of buffers in windows, see Buffers and Windows.
There are, in general, many buffers in an Emacs session. At any time, one of them is designated the current buffer—the buffer in which most editing takes place. Most of the primitives for examining or changing text operate implicitly on the current buffer (see Text).
Normally, the buffer displayed in the selected window is the current
buffer, but this is not always so: a Lisp program can temporarily
designate any buffer as current in order to operate on its contents,
without changing what is displayed on the screen. The most basic
function for designating a current buffer is set-buffer.
This function returns the current buffer.
(current-buffer) => #<buffer buffers.texi>
This function makes buffer-or-name the current buffer. buffer-or-name must be an existing buffer or the name of an existing buffer. The return value is the buffer made current.
This function does not display the buffer in any window, so the user cannot necessarily see the buffer. But Lisp programs will now operate on it.
When an editing command returns to the editor command loop, Emacs
automatically calls set-buffer on the buffer shown in the
selected window. This is to prevent confusion: it ensures that the
buffer that the cursor is in, when Emacs reads a command, is the
buffer to which that command applies (see Command Loop). Thus,
you should not use set-buffer to switch visibly to a different
buffer; for that, use the functions described in Switching Buffers.
When writing a Lisp function, do not rely on this behavior of the command loop to restore the current buffer after an operation. Editing commands can also be called as Lisp functions by other programs, not just from the command loop; it is convenient for the caller if the subroutine does not change which buffer is current (unless, of course, that is the subroutine's purpose).
To operate temporarily on another buffer, put the set-buffer
within a save-current-buffer form. Here, as an example, is a
simplified version of the command append-to-buffer:
(defun append-to-buffer (buffer start end)
"Append the text of the region to BUFFER."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(save-current-buffer
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end))))
Here, we bind a local variable to record the current buffer, and then
save-current-buffer arranges to make it current again later.
Next, set-buffer makes the specified buffer current, and
insert-buffer-substring copies the string from the original
buffer to the specified (and now current) buffer.
Alternatively, we can use the with-current-buffer macro:
(defun append-to-buffer (buffer start end)
"Append the text of the region to BUFFER."
(interactive "BAppend to buffer: \nr")
(let ((oldbuf (current-buffer)))
(with-current-buffer (get-buffer-create buffer)
(insert-buffer-substring oldbuf start end))))
In either case, if the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. If it is not displayed in any window, you will not see the change immediately on the screen. The command causes the buffer to become current temporarily, but does not cause it to be displayed.
If you make local bindings (with let or function arguments)
for a variable that may also have buffer-local bindings, make sure
that the same buffer is current at the beginning and at the end of the
local binding's scope. Otherwise you might bind it in one buffer and
unbind it in another!
Do not rely on using set-buffer to change the current buffer
back, because that won't do the job if a quit happens while the wrong
buffer is current. For instance, in the previous example, it would
have been wrong to do this:
(let ((oldbuf (current-buffer)))
(set-buffer (get-buffer-create buffer))
(insert-buffer-substring oldbuf start end)
(set-buffer oldbuf))
Using save-current-buffer or with-current-buffer, as we
did, correctly handles quitting, errors, and throw, as well as
ordinary evaluation.
The
save-current-bufferspecial form saves the identity of the current buffer, evaluates the body forms, and finally restores that buffer as current. The return value is the value of the last form in body. The current buffer is restored even in case of an abnormal exit viathrowor error (see Nonlocal Exits).If the buffer that used to be current has been killed by the time of exit from
save-current-buffer, then it is not made current again, of course. Instead, whichever buffer was current just before exit remains current.
The
with-current-buffermacro saves the identity of the current buffer, makes buffer-or-name current, evaluates the body forms, and finally restores the current buffer. buffer-or-name must specify an existing buffer or the name of an existing buffer.The return value is the value of the last form in body. The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).
The
with-temp-buffermacro evaluates the body forms with a temporary buffer as the current buffer. It saves the identity of the current buffer, creates a temporary buffer and makes it current, evaluates the body forms, and finally restores the previous current buffer while killing the temporary buffer. By default, undo information (see Undo) is not recorded in the buffer created by this macro (but body can enable that, if needed).The return value is the value of the last form in body. You can return the contents of the temporary buffer by using
(buffer-string)as the last form.The current buffer is restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).See also
with-temp-filein Writing to Files.
Each buffer has a unique name, which is a string. Many of the functions that work on buffers accept either a buffer or a buffer name as an argument. Any argument called buffer-or-name is of this sort, and an error is signaled if it is neither a string nor a buffer. Any argument called buffer must be an actual buffer object, not a name.
Buffers that are ephemeral and generally uninteresting to the user
have names starting with a space, so that the list-buffers and
buffer-menu commands don't mention them (but if such a buffer
visits a file, it is mentioned). A name starting with
space also initially disables recording undo information; see
Undo.
This function returns the name of buffer as a string. buffer defaults to the current buffer.
If
buffer-namereturnsnil, it means that buffer has been killed. See Killing Buffers.(buffer-name) => "buffers.texi" (setq foo (get-buffer "temp")) => #<buffer temp> (kill-buffer foo) => nil (buffer-name foo) => nil foo => #<killed buffer>
This function renames the current buffer to newname. An error is signaled if newname is not a string.
Ordinarily,
rename-buffersignals an error if newname is already in use. However, if unique is non-nil, it modifies newname to make a name that is not in use. Interactively, you can make unique non-nilwith a numeric prefix argument. (This is how the commandrename-uniquelyis implemented.)This function returns the name actually given to the buffer.
This function returns the buffer specified by buffer-or-name. If buffer-or-name is a string and there is no buffer with that name, the value is
nil. If buffer-or-name is a buffer, it is returned as given; that is not very useful, so the argument is usually a name. For example:(setq b (get-buffer "lewis")) => #<buffer lewis> (get-buffer b) => #<buffer lewis> (get-buffer "Frazzle-nots") => nilSee also the function
get-buffer-createin Creating Buffers.
This function returns a name that would be unique for a new buffer—but does not create the buffer. It starts with starting-name, and produces a name not currently in use for any buffer by appending a number inside of `<...>'. It starts at 2 and keeps incrementing the number until it is not the name of an existing buffer.
If the optional second argument ignore is non-
nil, it should be a string, a potential buffer name. It means to consider that potential buffer acceptable, if it is tried, even it is the name of an existing buffer (which would normally be rejected). Thus, if buffers named `foo', `foo<2>', `foo<3>' and `foo<4>' exist,(generate-new-buffer-name "foo") => "foo<5>" (generate-new-buffer-name "foo" "foo<3>") => "foo<3>" (generate-new-buffer-name "foo" "foo<6>") => "foo<5>"See the related function
generate-new-bufferin Creating Buffers.
The buffer file name is the name of the file that is visited in
that buffer. When a buffer is not visiting a file, its buffer file name
is nil. Most of the time, the buffer name is the same as the
nondirectory part of the buffer file name, but the buffer file name and
the buffer name are distinct and can be set independently.
See Visiting Files.
This function returns the absolute file name of the file that buffer is visiting. If buffer is not visiting any file,
buffer-file-namereturnsnil. If buffer is not supplied, it defaults to the current buffer.(buffer-file-name (other-buffer)) => "/usr/user/lewis/manual/files.texi"
This buffer-local variable contains the name of the file being visited in the current buffer, or
nilif it is not visiting a file. It is a permanent local variable, unaffected bykill-all-local-variables.buffer-file-name => "/usr/user/lewis/manual/buffers.texi"It is risky to change this variable's value without doing various other things. Normally it is better to use
set-visited-file-name(see below); some of the things done there, such as changing the buffer name, are not strictly necessary, but others are essential to avoid confusing Emacs.
This buffer-local variable holds the abbreviated truename of the file visited in the current buffer, or
nilif no file is visited. It is a permanent local, unaffected bykill-all-local-variables. See Truenames, and abbreviate-file-name.
This buffer-local variable holds the file number and directory device number of the file visited in the current buffer, or
nilif no file or a nonexistent file is visited. It is a permanent local, unaffected bykill-all-local-variables.The value is normally a list of the form
(filenum devnum). This pair of numbers uniquely identifies the file among all files accessible on the system. See the functionfile-attributes, in File Attributes, for more information about them.If
buffer-file-nameis the name of a symbolic link, then both numbers refer to the recursive target.
This function returns the buffer visiting file filename. If there is no such buffer, it returns
nil. The argument filename, which must be a string, is expanded (see File Name Expansion), then compared against the visited file names of all live buffers. Note that the buffer'sbuffer-file-namemust match the expansion of filename exactly. This function will not recognize other names for the same file.(get-file-buffer "buffers.texi") => #<buffer buffers.texi>In unusual circumstances, there can be more than one buffer visiting the same file name. In such cases, this function returns the first such buffer in the buffer list.
This is like
get-file-buffer, except that it can return any buffer visiting the file possibly under a different name. That is, the buffer'sbuffer-file-namedoes not need to match the expansion of filename exactly, it only needs to refer to the same file. If predicate is non-nil, it should be a function of one argument, a buffer visiting filename. The buffer is only considered a suitable return value if predicate returns non-nil. If it can not find a suitable buffer to return,find-buffer-visitingreturnsnil.
If filename is a non-empty string, this function changes the name of the file visited in the current buffer to filename. (If the buffer had no visited file, this gives it one.) The next time the buffer is saved it will go in the newly-specified file.
This command marks the buffer as modified, since it does not (as far as Emacs knows) match the contents of filename, even if it matched the former visited file. It also renames the buffer to correspond to the new file name, unless the new name is already in use.
If filename is
nilor the empty string, that stands for “no visited file”. In this case,set-visited-file-namemarks the buffer as having no visited file, without changing the buffer's modified flag.Normally, this function asks the user for confirmation if there already is a buffer visiting filename. If no-query is non-
nil, that prevents asking this question. If there already is a buffer visiting filename, and the user confirms or no-query is non-nil, this function makes the new buffer name unique by appending a number inside of `<...>' to filename.If along-with-file is non-
nil, that means to assume that the former visited file has been renamed to filename. In this case, the command does not change the buffer's modified flag, nor the buffer's recorded last file modification time as reported byvisited-file-modtime(see Modification Time). If along-with-file isnil, this function clears the recorded last file modification time, after whichvisited-file-modtimereturns zero.When the function
set-visited-file-nameis called interactively, it prompts for filename in the minibuffer.
This buffer-local variable specifies a string to display in a buffer listing where the visited file name would go, for buffers that don't have a visited file name. Dired buffers use this variable.
Emacs keeps a flag called the modified flag for each buffer, to
record whether you have changed the text of the buffer. This flag is
set to t whenever you alter the contents of the buffer, and
cleared to nil when you save it. Thus, the flag shows whether
there are unsaved changes. The flag value is normally shown in the mode
line (see Mode Line Variables), and controls saving (see Saving Buffers) and auto-saving (see Auto-Saving).
Some Lisp programs set the flag explicitly. For example, the function
set-visited-file-name sets the flag to t, because the text
does not match the newly-visited file, even if it is unchanged from the
file formerly visited.
The functions that modify the contents of buffers are described in Text.
This function returns
tif the buffer buffer has been modified since it was last read in from a file or saved, ornilotherwise. If buffer is not supplied, the current buffer is tested.
This function marks the current buffer as modified if flag is non-
nil, or as unmodified if the flag isnil.Another effect of calling this function is to cause unconditional redisplay of the mode line for the current buffer. In fact, the function
force-mode-line-updateworks by doing this:(set-buffer-modified-p (buffer-modified-p))
Like
set-buffer-modified-p, but does not force redisplay of mode lines.
This command marks the current buffer as unmodified, and not needing to be saved. If arg is non-
nil, it marks the buffer as modified, so that it will be saved at the next suitable occasion. Interactively, arg is the prefix argument.Don't use this function in programs, since it prints a message in the echo area; use
set-buffer-modified-p(above) instead.
This function returns buffer's modification-count. This is a counter that increments every time the buffer is modified. If buffer is
nil(or omitted), the current buffer is used. The counter can wrap around occasionally.
This function returns buffer's character-change modification-count. Changes to text properties leave this counter unchanged; however, each time text is inserted or removed from the buffer, the counter is reset to the value that would be returned by
buffer-modified-tick. By comparing the values returned by twobuffer-chars-modified-tickcalls, you can tell whether a character change occurred in that buffer in between the calls. If buffer isnil(or omitted), the current buffer is used.
Suppose that you visit a file and make changes in its buffer, and meanwhile the file itself is changed on disk. At this point, saving the buffer would overwrite the changes in the file. Occasionally this may be what you want, but usually it would lose valuable information. Emacs therefore checks the file's modification time using the functions described below before saving the file. (See File Attributes, for how to examine a file's modification time.)
This function compares what buffer (by default, the current-buffer) has recorded for the modification time of its visited file against the actual modification time of the file as recorded by the operating system. The two should be the same unless some other process has written the file since Emacs visited or saved it.
The function returns
tif the last actual modification time and Emacs's recorded modification time are the same,nilotherwise. It also returnstif the buffer has no recorded last modification time, that is ifvisited-file-modtimewould return zero.It always returns
tfor buffers that are not visiting a file, even ifvisited-file-modtimereturns a non-zero value. For instance, it always returnstfor dired buffers. It returnstfor buffers that are visiting a file that does not exist and never existed, butnilfor file-visiting buffers whose file has been deleted.
This function clears out the record of the last modification time of the file being visited by the current buffer. As a result, the next attempt to save this buffer will not complain of a discrepancy in file modification times.
This function is called in
set-visited-file-nameand other exceptional places where the usual test to avoid overwriting a changed file should not be done.
This function returns the current buffer's recorded last file modification time, as a list of the form
(high low microsec picosec). (This is the same format thatfile-attributesuses to return time values; see File Attributes.)If the buffer has no recorded last modification time, this function returns zero. This case occurs, for instance, if the buffer is not visiting a file or if the time has been explicitly cleared by
clear-visited-file-modtime. Note, however, thatvisited-file-modtimereturns a list for some non-file buffers too. For instance, in a Dired buffer listing a directory, it returns the last modification time of that directory, as recorded by Dired.If the buffer is not visiting a file, this function returns -1.
This function updates the buffer's record of the last modification time of the visited file, to the value specified by time if time is not
nil, and otherwise to the last modification time of the visited file.If time is neither
nilnor zero, it should have the form(high low microsec picosec), the format used bycurrent-time(see Time of Day).This function is useful if the buffer was not read from the file normally, or if the file itself has been changed for some known benign reason.
This function is used to ask a user how to proceed after an attempt to modify an buffer visiting file filename when the file is newer than the buffer text. Emacs detects this because the modification time of the file on disk is newer than the last save-time of the buffer. This means some other program has probably altered the file.
Depending on the user's answer, the function may return normally, in which case the modification of the buffer proceeds, or it may signal a
file-supersessionerror with data(filename), in which case the proposed buffer modification is not allowed.This function is called automatically by Emacs on the proper occasions. It exists so you can customize Emacs by redefining it. See the file userlock.el for the standard definition.
See also the file locking mechanism in File Locks.
If a buffer is read-only, then you cannot change its contents, although you may change your view of the contents by scrolling and narrowing.
Read-only buffers are used in two kinds of situations:
Here, the purpose is to inform the user that editing the buffer with the aim of saving it in the file may be futile or undesirable. The user who wants to change the buffer text despite this can do so after clearing the read-only flag with C-x C-q.
The special commands of these modes bind buffer-read-only to
nil (with let) or bind inhibit-read-only to
t around the places where they themselves change the text.
This buffer-local variable specifies whether the buffer is read-only. The buffer is read-only if this variable is non-
nil. However, characters that have theinhibit-read-onlytext property can still be modified. See inhibit-read-only.
If this variable is non-
nil, then read-only buffers and, depending on the actual value, some or all read-only characters may be modified. Read-only characters in a buffer are those that have a non-nilread-onlytext property. See Special Properties, for more information about text properties.If
inhibit-read-onlyist, allread-onlycharacter properties have no effect. Ifinhibit-read-onlyis a list, thenread-onlycharacter properties have no effect if they are members of the list (comparison is done witheq).
This is the mode command for Read Only minor mode, a buffer-local minor mode. When the mode is enabled,
buffer-read-onlyis non-nilin the buffer; when disabled,buffer-read-onlyisnilin the buffer. The calling convention is the same as for other minor mode commands (see Minor Mode Conventions).This minor mode mainly serves as a wrapper for
buffer-read-only; unlike most minor modes, there is no separateread-only-modevariable. Even when Read Only mode is disabled, characters with non-nilread-onlytext properties remain read-only. To temporarily ignore all read-only states, bindinhibit-read-only, as described above.When enabling Read Only mode, this mode command also enables View mode if the option
view-read-onlyis non-nil. See Miscellaneous Buffer Operations. When disabling Read Only mode, it disables View mode if View mode was enabled.
This function signals a
buffer-read-onlyerror if the current buffer is read-only. If the text at position (which defaults to point) has theinhibit-read-onlytext property set, the error will not be raised.See Using Interactive, for another way to signal an error if the current buffer is read-only.
The buffer list is a list of all live buffers. The order of the
buffers in this list is based primarily on how recently each buffer has
been displayed in a window. Several functions, notably
other-buffer, use this ordering. A buffer list displayed for the
user also follows this order.
Creating a buffer adds it to the end of the buffer list, and killing
a buffer removes it from that list. A buffer moves to the front of
this list whenever it is chosen for display in a window
(see Switching Buffers) or a window displaying it is selected
(see Selecting Windows). A buffer moves to the end of the list
when it is buried (see bury-buffer, below). There are no
functions available to the Lisp programmer which directly manipulate
the buffer list.
In addition to the fundamental buffer list just described, Emacs
maintains a local buffer list for each frame, in which the buffers that
have been displayed (or had their windows selected) in that frame come
first. (This order is recorded in the frame's buffer-list frame
parameter; see Buffer Parameters.) Buffers never displayed in
that frame come afterward, ordered according to the fundamental buffer
list.
This function returns the buffer list, including all buffers, even those whose names begin with a space. The elements are actual buffers, not their names.
If frame is a frame, this returns frame's local buffer list. If frame is
nilor omitted, the fundamental buffer list is used: the buffers appear in order of most recent display or selection, regardless of which frames they were displayed on.(buffer-list) => (#<buffer buffers.texi> #<buffer *Minibuf-1*> #<buffer buffer.c> #<buffer *Help*> #<buffer TAGS>) ;; Note that the name of the minibuffer ;; begins with a space! (mapcar (function buffer-name) (buffer-list)) => ("buffers.texi" " *Minibuf-1*" "buffer.c" "*Help*" "TAGS")
The list returned by buffer-list is constructed specifically;
it is not an internal Emacs data structure, and modifying it has no
effect on the order of buffers. If you want to change the order of
buffers in the fundamental buffer list, here is an easy way:
(defun reorder-buffer-list (new-list)
(while new-list
(bury-buffer (car new-list))
(setq new-list (cdr new-list))))
With this method, you can specify any order for the list, but there is no danger of losing a buffer or adding something that is not a valid live buffer.
To change the order or value of a specific frame's buffer list, set
that frame's buffer-list parameter with
modify-frame-parameters (see Parameter Access).
This function returns the first buffer in the buffer list other than buffer. Usually, this is the buffer appearing in the most recently selected window (in frame frame or else the selected frame, see Input Focus), aside from buffer. Buffers whose names start with a space are not considered at all.
If buffer is not supplied (or if it is not a live buffer), then
other-bufferreturns the first buffer in the selected frame's local buffer list. (If frame is non-nil, it returns the first buffer in frame's local buffer list instead.)If frame has a non-
nilbuffer-predicateparameter, thenother-bufferuses that predicate to decide which buffers to consider. It calls the predicate once for each buffer, and if the value isnil, that buffer is ignored. See Buffer Parameters.If visible-ok is
nil,other-bufferavoids returning a buffer visible in any window on any visible frame, except as a last resort. If visible-ok is non-nil, then it does not matter whether a buffer is displayed somewhere or not.If no suitable buffer exists, the buffer *scratch* is returned (and created, if necessary).
This function returns the last buffer in frame's buffer list other than buffer. If frame is omitted or
nil, it uses the selected frame's buffer list.The argument visible-ok is handled as with
other-buffer, see above. If no suitable buffer can be found, the buffer *scratch* is returned.
This command puts buffer-or-name at the end of the buffer list, without changing the order of any of the other buffers on the list. This buffer therefore becomes the least desirable candidate for
other-bufferto return. The argument can be either a buffer itself or the name of one.This function operates on each frame's
buffer-listparameter as well as the fundamental buffer list; therefore, the buffer that you bury will come last in the value of(buffer-listframe)and in the value of(buffer-list). In addition, it also puts the buffer at the end of the list of buffer of the selected window (see Window History) provided it is shown in that window.If buffer-or-name is
nilor omitted, this means to bury the current buffer. In addition, if the current buffer is displayed in the selected window, this makes sure that the window is either deleted or another buffer is shown in it. More precisely, if the selected window is dedicated (see Dedicated Windows) and there are other windows on its frame, the window is deleted. If it is the only window on its frame and that frame is not the only frame on its terminal, the frame is dismissed by calling the function specified byframe-auto-hide-function(see Quitting Windows). Otherwise, it callsswitch-to-prev-buffer(see Window History) to show another buffer in that window. If buffer-or-name is displayed in some other window, it remains displayed there.To replace a buffer in all the windows that display it, use
replace-buffer-in-windows, See Buffers and Windows.
This command switches to the last buffer in the local buffer list of the selected frame. More precisely, it calls the function
switch-to-buffer(see Switching Buffers), to display the buffer returned bylast-buffer(see above), in the selected window.
This is a normal hook run whenever the buffer list changes. Functions (implicitly) running this hook are
get-buffer-create(see Creating Buffers),rename-buffer(see Buffer Names),kill-buffer(see Killing Buffers),bury-buffer(see above) andselect-window(see Selecting Windows).
This section describes the two primitives for creating buffers.
get-buffer-create creates a buffer if it finds no existing buffer
with the specified name; generate-new-buffer always creates a new
buffer and gives it a unique name.
Other functions you can use to create buffers include
with-output-to-temp-buffer (see Temporary Displays) and
create-file-buffer (see Visiting Files). Starting a
subprocess can also create a buffer (see Processes).
This function returns a buffer named buffer-or-name. The buffer returned does not become the current buffer—this function does not change which buffer is current.
buffer-or-name must be either a string or an existing buffer. If it is a string and a live buffer with that name already exists,
get-buffer-createreturns that buffer. If no such buffer exists, it creates a new buffer. If buffer-or-name is a buffer instead of a string, it is returned as given, even if it is dead.(get-buffer-create "foo") => #<buffer foo>The major mode for a newly created buffer is set to Fundamental mode. (The default value of the variable
major-modeis handled at a higher level; see Auto Major Mode.) If the name begins with a space, the buffer initially disables undo information recording (see Undo).
This function returns a newly created, empty buffer, but does not make it current. The name of the buffer is generated by passing name to the function
generate-new-buffer-name(see Buffer Names). Thus, if there is no buffer named name, then that is the name of the new buffer; if that name is in use, a suffix of the form `<n>', where n is an integer, is appended to name.An error is signaled if name is not a string.
(generate-new-buffer "bar") => #<buffer bar> (generate-new-buffer "bar") => #<buffer bar<2>> (generate-new-buffer "bar") => #<buffer bar<3>>The major mode for the new buffer is set to Fundamental mode. The default value of the variable
major-modeis handled at a higher level. See Auto Major Mode.
Killing a buffer makes its name unknown to Emacs and makes the memory space it occupied available for other use.
The buffer object for the buffer that has been killed remains in
existence as long as anything refers to it, but it is specially marked
so that you cannot make it current or display it. Killed buffers retain
their identity, however; if you kill two distinct buffers, they remain
distinct according to eq although both are dead.
If you kill a buffer that is current or displayed in a window, Emacs automatically selects or displays some other buffer instead. This means that killing a buffer can change the current buffer. Therefore, when you kill a buffer, you should also take the precautions associated with changing the current buffer (unless you happen to know that the buffer being killed isn't current). See Current Buffer.
If you kill a buffer that is the base buffer of one or more indirect buffers (see Indirect Buffers), the indirect buffers are automatically killed as well.
The buffer-name of a buffer is nil if, and only if,
the buffer is killed. A buffer that has not been killed is called a
live buffer. To test whether a buffer is live or killed, use
the function buffer-live-p (see below).
This function kills the buffer buffer-or-name, freeing all its memory for other uses or to be returned to the operating system. If buffer-or-name is
nilor omitted, it kills the current buffer.Any processes that have this buffer as the
process-bufferare sent theSIGHUP(hangup) signal, which normally causes them to terminate. See Signals to Processes.If the buffer is visiting a file and contains unsaved changes,
kill-bufferasks the user to confirm before the buffer is killed. It does this even if not called interactively. To prevent the request for confirmation, clear the modified flag before callingkill-buffer. See Buffer Modification.This function calls
replace-buffer-in-windowsfor cleaning up all windows currently displaying the buffer to be killed.Killing a buffer that is already dead has no effect.
This function returns
tif it actually killed the buffer. It returnsnilif the user refuses to confirm or if buffer-or-name was already dead.(kill-buffer "foo.unchanged") => t (kill-buffer "foo.changed") ---------- Buffer: Minibuffer ---------- Buffer foo.changed modified; kill anyway? (yes or no) yes ---------- Buffer: Minibuffer ---------- => t
Before confirming unsaved changes,
kill-buffercalls the functions in the listkill-buffer-query-functions, in order of appearance, with no arguments. The buffer being killed is the current buffer when they are called. The idea of this feature is that these functions will ask for confirmation from the user. If any of them returnsnil,kill-bufferspares the buffer's life.
This is a normal hook run by
kill-bufferafter asking all the questions it is going to ask, just before actually killing the buffer. The buffer to be killed is current when the hook functions run. See Hooks. This variable is a permanent local, so its local binding is not cleared by changing major modes.
This variable, if non-
nilin a particular buffer, tellssave-buffers-kill-emacsandsave-some-buffers(if the second optional argument to that function ist) to offer to save that buffer, just as they offer to save file-visiting buffers. See Definition of save-some-buffers. The variablebuffer-offer-saveautomatically becomes buffer-local when set for any reason. See Buffer-Local Variables.
This variable, if non-
nilin a particular buffer, tellssave-buffers-kill-emacsandsave-some-buffersto save this buffer (if it's modified) without asking the user. The variable automatically becomes buffer-local when set for any reason.
This function returns
tif object is a live buffer (a buffer which has not been killed),nilotherwise.
An indirect buffer shares the text of some other buffer, which is called the base buffer of the indirect buffer. In some ways it is the analogue, for buffers, of a symbolic link among files. The base buffer may not itself be an indirect buffer.
The text of the indirect buffer is always identical to the text of its base buffer; changes made by editing either one are visible immediately in the other. This includes the text properties as well as the characters themselves.
In all other respects, the indirect buffer and its base buffer are completely separate. They have different names, independent values of point, independent narrowing, independent markers and overlays (though inserting or deleting text in either buffer relocates the markers and overlays for both), independent major modes, and independent buffer-local variable bindings.
An indirect buffer cannot visit a file, but its base buffer can. If you try to save the indirect buffer, that actually saves the base buffer.
Killing an indirect buffer has no effect on its base buffer. Killing the base buffer effectively kills the indirect buffer in that it cannot ever again be the current buffer.
This creates and returns an indirect buffer named name whose base buffer is base-buffer. The argument base-buffer may be a live buffer or the name (a string) of an existing buffer. If name is the name of an existing buffer, an error is signaled.
If clone is non-
nil, then the indirect buffer originally shares the state of base-buffer such as major mode, minor modes, buffer local variables and so on. If clone is omitted ornilthe indirect buffer's state is set to the default state for new buffers.If base-buffer is an indirect buffer, its base buffer is used as the base for the new buffer. If, in addition, clone is non-
nil, the initial state is copied from the actual base buffer, not from base-buffer.
This function creates and returns a new indirect buffer that shares the current buffer's base buffer and copies the rest of the current buffer's attributes. (If the current buffer is not indirect, it is used as the base buffer.)
If display-flag is non-
nil, that means to display the new buffer by callingpop-to-buffer. If norecord is non-nil, that means not to put the new buffer to the front of the buffer list.
This function returns the base buffer of buffer, which defaults to the current buffer. If buffer is not indirect, the value is
nil. Otherwise, the value is another buffer, which is never an indirect buffer.
Specialized modes sometimes need to let the user access from the same buffer several vastly different types of text. For example, you may need to display a summary of the buffer text, in addition to letting the user access the text itself.
This could be implemented with multiple buffers (kept in sync when the user edits the text), or with narrowing (see Narrowing). But these alternatives might sometimes become tedious or prohibitively expensive, especially if each type of text requires expensive buffer-global operations in order to provide correct display and editing commands.
Emacs provides another facility for such modes: you can quickly swap
buffer text between two buffers with buffer-swap-text. This
function is very fast because it doesn't move any text, it only
changes the internal data structures of the buffer object to point to
a different chunk of text. Using it, you can pretend that a group of
two or more buffers are actually a single virtual buffer that holds
the contents of all the individual buffers together.
This function swaps the text of the current buffer and that of its argument buffer. It signals an error if one of the two buffers is an indirect buffer (see Indirect Buffers) or is a base buffer of an indirect buffer.
All the buffer properties that are related to the buffer text are swapped as well: the positions of point and mark, all the markers, the overlays, the text properties, the undo list, the value of the
enable-multibyte-charactersflag (see enable-multibyte-characters), etc.
If you use buffer-swap-text on a file-visiting buffer, you
should set up a hook to save the buffer's original text rather than
what it was swapped with. write-region-annotate-functions
works for this purpose. You should probably set
buffer-saved-size to −2 in the buffer, so that changes
in the text it is swapped with will not interfere with auto-saving.
Emacs buffers are implemented using an invisible gap to make insertion and deletion faster. Insertion works by filling in part of the gap, and deletion adds to the gap. Of course, this means that the gap must first be moved to the locus of the insertion or deletion. Emacs moves the gap only when you try to insert or delete. This is why your first editing command in one part of a large buffer, after previously editing in another far-away part, sometimes involves a noticeable delay.
This mechanism works invisibly, and Lisp code should never be affected by the gap's current location, but these functions are available for getting information about the gap status.
This chapter describes the functions and variables related to Emacs windows. See Frames, for how windows are assigned an area of screen available for Emacs to use. See Display, for information on how text is displayed in windows.
A window is an area of the screen that is used to display a buffer (see Buffers). In Emacs Lisp, windows are represented by a special Lisp object type.
Windows are grouped into frames (see Frames). Each frame contains at least one window; the user can subdivide it into multiple, non-overlapping windows to view several buffers at once. Lisp programs can use multiple windows for a variety of purposes. In Rmail, for example, you can view a summary of message titles in one window, and the contents of the selected message in another window.
Emacs uses the word “window” with a different meaning than in graphical desktop environments and window systems, such as the X Window System. When Emacs is run on X, each of its graphical X windows is an Emacs frame (containing one or more Emacs windows). When Emacs is run on a text terminal, the frame fills the entire terminal screen.
Unlike X windows, Emacs windows are tiled; they never overlap within the area of the frame. When a window is created, resized, or deleted, the change in window space is taken from or given to the adjacent windows, so that the total area of the frame is unchanged.
This function returns
tif object is a window (whether or not it displays a buffer). Otherwise, it returnsnil.
A live window is one that is actually displaying a buffer in a frame.
This function returns
tif object is a live window andnilotherwise. A live window is one that displays a buffer.
The windows in each frame are organized into a window tree. See Windows and Frames. The leaf nodes of each window tree are live windows—the ones actually displaying buffers. The internal nodes of the window tree are internal windows, which are not live.
A valid window is one that is either live or internal. A valid window can be deleted, i.e., removed from its frame (see Deleting Windows); then it is no longer valid, but the Lisp object representing it might be still referenced from other Lisp objects. A deleted window may be made valid again by restoring a saved window configuration (see Window Configurations).
You can distinguish valid windows from deleted windows with
window-valid-p.
This function returns
tif object is a live window, or an internal window in a window tree. Otherwise, it returnsnil, including for the case where object is a deleted window.
In each frame, at any time, exactly one Emacs window is designated
as selected within the frame. For the selected frame, that
window is called the selected window—the one in which most
editing takes place, and in which the cursor for selected windows
appears (see Cursor Parameters). The selected window's buffer is
usually also the current buffer, except when set-buffer has
been used (see Current Buffer). As for non-selected frames, the
window selected within the frame becomes the selected window if the
frame is ever selected. See Selecting Windows.
This function returns the selected window (which is always a live window).
Sometimes several windows collectively and
cooperatively display a buffer, for example, under the management of
Follow Mode (see Follow Mode), where the windows together
display a bigger portion of the buffer than one window could alone.
It is often useful to consider such a window group as a single
entity. Several functions such as window-group-start
(see Window Start and End) allow you to do this by supplying, as
an argument, one of the windows as a stand in for the whole group.
When the selected window is a member of a group of windows, this function returns a list of the windows in the group, ordered such that the first window in the list is displaying the earliest part of the buffer, and so on. Otherwise the function returns a list containing just the selected window.
The selected window is considered part of a group when the buffer local variable
selected-window-group-functionis set to a function. In this case,selected-window-groupcalls it with no arguments and returns its result (which should be the list of windows in the group).
Each window belongs to exactly one frame (see Frames).
This function returns the frame that the window window belongs to. If window is
nil, it defaults to the selected window.
This function returns a list of live windows belonging to the frame frame. If frame is omitted or
nil, it defaults to the selected frame.The optional argument minibuffer specifies whether to include the minibuffer window in the returned list. If minibuffer is
t, the minibuffer window is included. If minibuffer isnilor omitted, the minibuffer window is included only if it is active. If minibuffer is neithernilnort, the minibuffer window is never included.The optional argument window, if non-
nil, should be a live window on the specified frame; then window will be the first element in the returned list. If window is omitted ornil, the window selected within the frame is the first element.
Windows in the same frame are organized into a window tree, whose leaf nodes are the live windows. The internal nodes of a window tree are not live; they exist for the purpose of organizing the relationships between live windows. The root node of a window tree is called the root window. It can be either a live window (if the frame has just one window), or an internal window.
A minibuffer window (see Minibuffer Windows) is not part of its
frame's window tree unless the frame is a minibuffer-only frame.
Nonetheless, most of the functions in this section accept the
minibuffer window as an argument. Also, the function
window-tree described at the end of this section lists the
minibuffer window alongside the actual window tree.
This function returns the root window for frame-or-window. The argument frame-or-window should be either a window or a frame; if omitted or
nil, it defaults to the selected frame. If frame-or-window is a window, the return value is the root window of that window's frame.
When a window is split, there are two live windows where previously there was one. One of these is represented by the same Lisp window object as the original window, and the other is represented by a newly-created Lisp window object. Both of these live windows become leaf nodes of the window tree, as child windows of a single internal window. If necessary, Emacs automatically creates this internal window, which is also called the parent window, and assigns it to the appropriate position in the window tree. A set of windows that share the same parent are called siblings.
This function returns the parent window of window. If window is omitted or
nil, it defaults to the selected window. The return value isnilif window has no parent (i.e., it is a minibuffer window or the root window of its frame).
Each internal window always has at least two child windows. If this number falls to one as a result of window deletion, Emacs automatically deletes the internal window, and its sole remaining child window takes its place in the window tree.
Each child window can be either a live window, or an internal window (which in turn would have its own child windows). Therefore, each internal window can be thought of as occupying a certain rectangular screen area—the union of the areas occupied by the live windows that are ultimately descended from it.
For each internal window, the screen areas of the immediate children are arranged either vertically or horizontally (never both). If the child windows are arranged one above the other, they are said to form a vertical combination; if they are arranged side by side, they are said to form a horizontal combination. Consider the following example:
______________________________________
| ______ ____________________________ |
|| || __________________________ ||
|| ||| |||
|| ||| |||
|| ||| |||
|| |||____________W4____________|||
|| || __________________________ ||
|| ||| |||
|| ||| |||
|| |||____________W5____________|||
||__W2__||_____________W3_____________ |
|__________________W1__________________|
The root window of this frame is an internal window, W1. Its child windows form a horizontal combination, consisting of the live window W2 and the internal window W3. The child windows of W3 form a vertical combination, consisting of the live windows W4 and W5. Hence, the live windows in this window tree are W2, W4, and W5.
The following functions can be used to retrieve a child window of an internal window, and the siblings of a child window.
This function returns the topmost child window of window, if window is an internal window whose children form a vertical combination. For any other type of window, the return value is
nil.
This function returns the leftmost child window of window, if window is an internal window whose children form a horizontal combination. For any other type of window, the return value is
nil.
This function returns the first child window of the internal window window—the topmost child window for a vertical combination, or the leftmost child window for a horizontal combination. If window is a live window, the return value is
nil.
This function returns a non-
nilvalue if and only if window is part of a vertical combination. If window is omitted ornil, it defaults to the selected one.If the optional argument horizontal is non-
nil, this means to return non-nilif and only if window is part of a horizontal combination.
This function returns the next sibling of the window window. If omitted or
nil, window defaults to the selected window. The return value isnilif window is the last child of its parent.
This function returns the previous sibling of the window window. If omitted or
nil, window defaults to the selected window. The return value isnilif window is the first child of its parent.
The functions window-next-sibling and
window-prev-sibling should not be confused with the functions
next-window and previous-window, which return the next
and previous window, respectively, in the cyclic ordering of windows
(see Cyclic Window Ordering).
You can use the following functions to find the first live window on a frame and the window nearest to a given window.
This function returns the live window at the upper left corner of the frame specified by frame-or-window. The argument frame-or-window must denote a window or a live frame and defaults to the selected frame. If frame-or-window specifies a window, this function returns the first window on that window's frame. Under the assumption that the frame from our canonical example is selected
(frame-first-window)returns W2.
This function returns the nearest live window in direction direction as seen from the position of
window-pointin window window. The argument direction must be one ofabove,below,leftorright. The optional argument window must denote a live window and defaults to the selected one.This function does not return a window whose
no-other-windowparameter is non-nil(see Window Parameters). If the nearest window'sno-other-windowparameter is non-nil, this function tries to find another window in the indicated direction whoseno-other-windowparameter isnil. If the optional argument ignore is non-nil, a window may be returned even if itsno-other-windowparameter is non-nil.If the optional argument sign is a negative number, it means to use the right or bottom edge of window as reference position instead of
window-point. If sign is a positive number, it means to use the left or top edge of window as reference position.If the optional argument wrap is non-
nil, this means to wrap direction around frame borders. For example, if window is at the top of the frame and direction isabove, then this function usually returns the frame's minibuffer window if it's active and a window at the bottom of the frame otherwise.If the optional argument mini is
nil, this means to return the minibuffer window if and only if it is currently active. If mini is non-nil, this function may return the minibuffer window even when it's not active. However, if wrap is non-nil, it always acts as if mini werenil.If it doesn't find a suitable window, this function returns
nil.
The following function allows the entire window tree of a frame to be retrieved:
This function returns a list representing the window tree for frame frame. If frame is omitted or
nil, it defaults to the selected frame.The return value is a list of the form
(root mini), where root represents the window tree of the frame's root window, and mini is the frame's minibuffer window.If the root window is live, root is that window itself. Otherwise, root is a list
(dir edges w1 w2...)where dir isnilfor a horizontal combination andtfor a vertical combination, edges gives the size and position of the combination, and the remaining elements are the child windows. Each child window may again be a window object (for a live window) or a list with the same format as above (for an internal window). The edges element is a list(left top right bottom), similar to the value returned bywindow-edges(see Coordinates and Windows).
The following schematic shows the structure of a live window:
____________________________________________
|______________ Header Line ______________|RD| ^
^ |LS|LM|LF| |RF|RM|RS| | |
| | | | | | | | | | |
Window | | | | Text Area | | | | | Window
Body | | | | | (Window Body) | | | | | Total
Height | | | | | | | | | Height
| | | | |<- Window Body Width ->| | | | | |
v |__|__|__|_______________________|__|__|__| | |
|_________ Horizontal Scroll Bar _________| | |
|_______________ Mode Line _______________|__| |
|_____________ Bottom Divider _______________| v
<---------- Window Total Width ------------>
At the center of the window is the text area, or body, where the buffer text is displayed. The text area can be surrounded by a series of optional areas. On the left and right, from innermost to outermost, these are the left and right fringes, denoted by LF and RF (see Fringes); the left and right margins, denoted by LM and RM in the schematic (see Display Margins); the left or right vertical scroll bar, only one of which is present at any time, denoted by LS and RS (see Scroll Bars); and the right divider, denoted by RD (see Window Dividers). At the top of the window is the header line (see Header Lines). At the bottom of the window are the horizontal scroll bar (see Scroll Bars); the mode line (see Mode Line Format); and the bottom divider (see Window Dividers).
Emacs provides miscellaneous functions for finding the height and
width of a window. The return value of many of these functions can be
specified either in units of pixels or in units of lines and columns.
On a graphical display, the latter actually correspond to the height and
width of a default character specified by the frame's default font
as returned by frame-char-height and frame-char-width
(see Frame Font). Thus, if a window is displaying text with a
different font or size, the reported line height and column width for
that window may differ from the actual number of text lines or columns
displayed within it.
The total height of a window is the number of lines comprising the window's body, the header line, the horizontal scroll bar, the mode line and the bottom divider (if any).
This function returns the total height, in lines, of the window window. If window is omitted or
nil, it defaults to the selected window. If window is an internal window, the return value is the total height occupied by its descendant windows.If a window's pixel height is not an integral multiple of its frame's default character height, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total heights of all its child windows internally equals the total height of their parent. This means that although two windows have the same pixel height, their internal total heights may differ by one line. This means also, that if window is vertically combined and has a next sibling, the topmost row of that sibling can be calculated as the sum of this window's topmost row and total height (see Coordinates and Windows)
If the optional argument round is
ceiling, this function returns the smallest integer larger than window's pixel height divided by the character height of its frame; if it isfloor, it returns the largest integer smaller than said value; with any other round it returns the internal value of windows's total height.
The total width of a window is the number of lines comprising the window's body, its margins, fringes, scroll bars and a right divider (if any).
This function returns the total width, in columns, of the window window. If window is omitted or
nil, it defaults to the selected window. If window is internal, the return value is the total width occupied by its descendant windows.If a window's pixel width is not an integral multiple of its frame's character width, the number of lines occupied by the window is rounded internally. This is done in a way such that, if the window is a parent window, the sum of the total widths of all its children internally equals the total width of their parent. This means that although two windows have the same pixel width, their internal total widths may differ by one column. This means also, that if this window is horizontally combined and has a next sibling, the leftmost column of that sibling can be calculated as the sum of this window's leftmost column and total width (see Coordinates and Windows). The optional argument round behaves as it does for
window-total-height.
This function returns either the total height in lines or the total width in columns of the window window. If horizontal is omitted or
nil, this is equivalent to callingwindow-total-heightfor window; otherwise it is equivalent to callingwindow-total-widthfor window. The optional argument round behaves as it does forwindow-total-height.
The following two functions can be used to return the total size of a window in units of pixels.
This function returns the total height of window window in pixels. window must be a valid window and defaults to the selected one.
The return value includes mode and header line, a horizontal scroll bar and a bottom divider, if any. If window is an internal window, its pixel height is the pixel height of the screen areas spanned by its children.
This function returns the width of window window in pixels. window must be a valid window and defaults to the selected one.
The return value includes the fringes and margins of window as well as any vertical dividers or scroll bars belonging to window. If window is an internal window, its pixel width is the width of the screen areas spanned by its children.
The following functions can be used to determine whether a given window has any adjacent windows.
This function returns non-
nilif window has no other window above or below it in its frame. More precisely, this means that the total height of window equals the total height of the root window on that frame. The minibuffer window does not count in this regard. If window is omitted ornil, it defaults to the selected window.
This function returns non-
nilif window has no other window to the left or right in its frame, i.e., its total width equals that of the root window on that frame. If window is omitted ornil, it defaults to the selected window.
The body height of a window is the height of its text area, which does not include a mode or header line, a horizontal scroll bar, or a bottom divider.
This function returns the height, in lines, of the body of window window. If window is omitted or
nil, it defaults to the selected window; otherwise it must be a live window.If the optional argument pixelwise is non-
nil, this function returns the body height of window counted in pixels.If pixelwise is
nil, the return value is rounded down to the nearest integer, if necessary. This means that if a line at the bottom of the text area is only partially visible, that line is not counted. It also means that the height of a window's body can never exceed its total height as returned bywindow-total-height.
The body width of a window is the width of its text area, which
does not include the scroll bar, fringes, margins or a right divider.
Note that when one or both fringes are removed (by setting their width
to zero), the display engine reserves two character cells, one on each
side of the window, for displaying the continuation and truncation
glyphs, which leaves 2 columns less for text display. (The function
window-max-chars-per-line, described below, takes this
peculiarity into account.)
This function returns the width, in columns, of the body of window window. If window is omitted or
nil, it defaults to the selected window; otherwise it must be a live window.If the optional argument pixelwise is non-
nil, this function returns the body width of window in units of pixels.If pixelwise is
nil, the return value is rounded down to the nearest integer, if necessary. This means that if a column on the right of the text area is only partially visible, that column is not counted. It also means that the width of a window's body can never exceed its total width as returned bywindow-total-width.
This function returns the body height or body width of window. If horizontal is omitted or
nil, it is equivalent to callingwindow-body-heightfor window; otherwise it is equivalent to callingwindow-body-width. In either case, the optional argument pixelwise is passed to the function called.
For compatibility with previous versions of Emacs,
window-height is an alias for window-total-height, and
window-width is an alias for window-body-width. These
aliases are considered obsolete and will be removed in the future.
The pixel heights of a window's mode and header line can be retrieved with the functions given below. Their return value is usually accurate unless the window has not been displayed before: In that case, the return value is based on an estimate of the font used for the window's frame.
This function returns the height in pixels of window's mode line. window must be a live window and defaults to the selected one. If window has no mode line, the return value is zero.
This function returns the height in pixels of window's header line. window must be a live window and defaults to the selected one. If window has no header line, the return value is zero.
Functions for retrieving the height and/or width of window dividers (see Window Dividers), fringes (see Fringes), scroll bars (see Scroll Bars), and display margins (see Display Margins) are described in the corresponding sections.
If your Lisp program needs to make layout decisions, you will find the following function useful:
This function returns the number of characters displayed in the specified face face in the specified window window (which must be a live window). If face was remapped (see Face Remapping), the information is returned for the remapped face. If omitted or
nil, face defaults to the default face, and window defaults to the selected window.Unlike
window-body-width, this function accounts for the actual size of face's font, instead of working in units of the canonical character width of window's frame (see Frame Font). It also accounts for space used by the continuation glyph, if window lacks one or both of its fringes.
Commands that change the size of windows (see Resizing Windows),
or split them (see Splitting Windows), obey the variables
window-min-height and window-min-width, which specify the
smallest allowable window height and width. They also obey the variable
window-size-fixed, with which a window can be fixed in
size (see Preserving Window Sizes).
This option specifies the minimum total height, in lines, of any window. Its value has to accommodate at least one text line as well as a mode and header line, a horizontal scroll bar and a bottom divider, if present.
This option specifies the minimum total width, in columns, of any window. Its value has to accommodate two text columns as well as margins, fringes, a scroll bar and a right divider, if present.
The following function tells how small a specific window can get taking
into account the sizes of its areas and the values of
window-min-height, window-min-width and
window-size-fixed (see Preserving Window Sizes).
This function returns the minimum size of window. window must be a valid window and defaults to the selected one. The optional argument horizontal non-
nilmeans to return the minimum number of columns of window; otherwise return the minimum number of window's lines.The return value makes sure that all components of window remain fully visible if window's size were actually set to it. With horizontal
nilit includes the mode and header line, the horizontal scroll bar and the bottom divider, if present. With horizontal non-nilit includes the margins and fringes, the vertical scroll bar and the right divider, if present.The optional argument ignore, if non-
nil, means ignore restrictions imposed by fixed size windows,window-min-heightorwindow-min-widthsettings. If ignore equalssafe, live windows may get as small aswindow-safe-min-heightlines andwindow-safe-min-widthcolumns. If ignore is a window, ignore restrictions for that window only. Any other non-nilvalue means ignore all of the above restrictions for all windows.The optional argument pixelwise non-
nilmeans to return the minimum size of window counted in pixels.
This section describes functions for resizing a window without changing the size of its frame. Because live windows do not overlap, these functions are meaningful only on frames that contain two or more windows: resizing a window also changes the size of a neighboring window. If there is just one window on a frame, its size cannot be changed except by resizing the frame (see Size and Position).
Except where noted, these functions also accept internal windows as arguments. Resizing an internal window causes its child windows to be resized to fit the same space.
This function returns delta if the size of window can be changed vertically by delta lines. If the optional argument horizontal is non-
nil, it instead returns delta if window can be resized horizontally by delta columns. It does not actually change the window size.If window is
nil, it defaults to the selected window.A positive value of delta means to check whether the window can be enlarged by that number of lines or columns; a negative value of delta means to check whether the window can be shrunk by that many lines or columns. If delta is non-zero, a return value of 0 means that the window cannot be resized.
Normally, the variables
window-min-heightandwindow-min-widthspecify the smallest allowable window size (see Window Sizes). However, if the optional argument ignore is non-nil, this function ignoreswindow-min-heightandwindow-min-width, as well aswindow-size-fixed. Instead, it considers the minimum-height window to be one consisting of a header and a mode line, a horizontal scrollbar and a bottom divider (if any), plus a text area one line tall; and a minimum-width window as one consisting of fringes, margins, a scroll bar and a right divider (if any), plus a text area two columns wide.If the optional argument pixelwise is non-
nil, delta is interpreted as pixels.
This function resizes window by delta increments. If horizontal is
nil, it changes the height by delta lines; otherwise, it changes the width by delta columns. A positive delta means to enlarge the window, and a negative delta means to shrink it.If window is
nil, it defaults to the selected window. If the window cannot be resized as demanded, an error is signaled.The optional argument ignore has the same meaning as for the function
window-resizableabove.If the optional argument pixelwise is non-
nil, delta will be interpreted as pixels.The choice of which window edges this function alters depends on the values of the option
window-combination-resizeand the combination limits of the involved windows; in some cases, it may alter both edges. See Recombining Windows. To resize by moving only the bottom or right edge of a window, use the functionadjust-window-trailing-edge.
This function moves window's bottom edge by delta lines. If optional argument horizontal is non-
nil, it instead moves the right edge by delta columns. If window isnil, it defaults to the selected window.If the optional argument pixelwise is non-
nil, delta is interpreted as pixels.A positive delta moves the edge downwards or to the right; a negative delta moves it upwards or to the left. If the edge cannot be moved as far as specified by delta, this function moves it as far as possible but does not signal a error.
This function tries to resize windows adjacent to the edge that is moved. If this is not possible for some reason (e.g., if that adjacent window is fixed-size), it may resize other windows.
If the value of this option is non-
nil, Emacs resizes windows in units of pixels. This currently affects functions likesplit-window(see Splitting Windows),maximize-window,minimize-window,fit-window-to-buffer,fit-frame-to-bufferandshrink-window-if-larger-than-buffer(all listed below).Note that when a frame's pixel size is not a multiple of its character size, at least one window may get resized pixelwise even if this option is
nil. The default value isnil.
The following commands resize windows in more specific ways. When called interactively, they act on the selected window.
This command adjusts the height or width of window to fit the text in it. It returns non-
nilif it was able to resize window, andnilotherwise. If window is omitted ornil, it defaults to the selected window. Otherwise, it should be a live window.If window is part of a vertical combination, this function adjusts window's height. The new height is calculated from the actual height of the accessible portion of its buffer. The optional argument max-height, if non-
nil, specifies the maximum total height that this function can give window. The optional argument min-height, if non-nil, specifies the minimum total height that it can give, which overrides the variablewindow-min-height. Both max-height and min-height are specified in lines and include mode and header line and a bottom divider, if any.If window is part of a horizontal combination and the value of the option
fit-window-to-buffer-horizontally(see below) is non-nil, this function adjusts window's height. The new width of window is calculated from the maximum length of its buffer's lines that follow the current start position of window. The optional argument max-width specifies a maximum width and defaults to the width of window's frame. The optional argument min-width specifies a minimum width and defaults towindow-min-width. Both max-width and min-width are specified in columns and include fringes, margins and scrollbars, if any.The optional argument preserve-size, if non-
nil, will install a parameter to preserve the size of window during future resize operations (see Preserving Window Sizes).If the option
fit-frame-to-buffer(see below) is non-nil, this function will try to resize the frame of window to fit its contents by callingfit-frame-to-buffer(see below).
If this is non-
nil,fit-window-to-buffercan resize windows horizontally. If this isnil(the default)fit-window-to-buffernever resizes windows horizontally. If this isonly, it can resize windows horizontally only. Any other value meansfit-window-to-buffercan resize windows in both dimensions.
If this option is non-
nil,fit-window-to-buffercan fit a frame to its buffer. A frame is fit if and only if its root window is a live window and this option is non-nil. If this ishorizontally, frames are fit horizontally only. If this isvertically, frames are fit vertically only. Any other non-nilvalue means frames can be resized in both dimensions.
If you have a frame that displays only one window, you can fit that
frame to its buffer using the command fit-frame-to-buffer.
This command adjusts the size of frame to display the contents of its buffer exactly. frame can be any live frame and defaults to the selected one. Fitting is done only if frame's root window is live. The arguments max-height, min-height, max-width and min-width specify bounds on the new total size of frame's root window. min-height and min-width default to the values of
window-min-heightandwindow-min-widthrespectively.If the optional argument only is
vertically, this function may resize the frame vertically only. If only ishorizontally, it may resize the frame horizontally only.
The behavior of fit-frame-to-buffer can be controlled with the
help of the two options listed next.
This option can be used to specify margins around frames to be fit by
fit-frame-to-buffer. Such margins can be useful to avoid, for example, that such frames overlap the taskbar.It specifies the numbers of pixels to be left free on the left, above, the right, and below a frame that shall be fit. The default specifies
nilfor each which means to use no margins. The value specified here can be overridden for a specific frame by that frame'sfit-frame-to-buffer-marginsparameter, if present.
This option specifies size boundaries for
fit-frame-to-buffer. It specifies the total maximum and minimum lines and maximum and minimum columns of the root window of any frame that shall be fit to its buffer. If any of these values is non-nil, it overrides the corresponding argument offit-frame-to-buffer.
This command attempts to reduce window's height as much as possible while still showing its full buffer, but no less than
window-min-heightlines. The return value is non-nilif the window was resized, andnilotherwise. If window is omitted ornil, it defaults to the selected window. Otherwise, it should be a live window.This command does nothing if the window is already too short to display all of its buffer, or if any of the buffer is scrolled off-screen, or if the window is the only live window in its frame.
This command calls
fit-window-to-buffer(see above) to do its work.
This function balances windows in a way that gives more space to full-width and/or full-height windows. If window-or-frame specifies a frame, it balances all windows on that frame. If window-or-frame specifies a window, it balances only that window and its siblings (see Windows and Frames).
This function attempts to give all windows on the selected frame approximately the same share of the screen area. Full-width or full-height windows are not given more space than other windows.
This function attempts to make window as large as possible, in both dimensions, without resizing its frame or deleting other windows. If window is omitted or
nil, it defaults to the selected window.
This function attempts to make window as small as possible, in both dimensions, without deleting it or resizing its frame. If window is omitted or
nil, it defaults to the selected window.
A window can get resized explicitly by using one of the functions from the preceding section or implicitly, for example, when resizing an adjacent window, when splitting or deleting a window (see Splitting Windows, see Deleting Windows) or when resizing the window's frame (see Size and Position).
It is possible to avoid implicit resizing of a specific window when there are one or more other resizable windows on the same frame. For this purpose, Emacs must be advised to preserve the size of that window. There are two basic ways to do that.
If this buffer-local variable is non-
nil, the size of any window displaying the buffer cannot normally be changed. Deleting a window or changing the frame's size may still change the window's size, if there is no choice.If the value is
height, then only the window's height is fixed; if the value iswidth, then only the window's width is fixed. Any other non-nilvalue fixes both the width and the height.If this variable is
nil, this does not necessarily mean that any window showing the buffer can be resized in the desired direction. To determine that, use the functionwindow-resizable. See Resizing Windows.
Often window-size-fixed is overly aggressive because it inhibits
any attempt to explicitly resize or split an affected window as well.
This may even happen after the window has been resized implicitly, for
example, when deleting an adjacent window or resizing the window's
frame. The following function tries hard to never disallow resizing
such a window explicitly:
This function (un-)marks the height of window window as preserved for future resize operations. window must be a live window and defaults to the selected one. If the optional argument horizontal is non-
nil, it (un-)marks the width of window as preserved.If the optional argument preserve is
t, this means to preserve the current height/width of window's body. The height/width of window will change only if Emacs has no better choice. Resizing a window whose height/width is preserved by this function never throws an error.If preserve is
nil, this means to stop preserving the height/width of window, lifting any respective restraint induced by a previous call of this function for window. Callingenlarge-window,shrink-windoworfit-window-to-bufferwith window as argument may also remove the respective restraint.
window-preserve-size is currently invoked by the following
functions:
fit-window-to-buffernil, the size established by
that function is preserved.
display-bufferpreserve-size entry, the size of the window produced
by that function is preserved.
window-preserve-size installs a window parameter (see Window Parameters) called preserved-size which is consulted by the
window resizing functions. This parameter will not prevent resizing the
window when the window shows another buffer than the one when
window-preserve-size was invoked or if its size has changed since
then.
The following function can be used to check whether the height of a particular window is preserved:
This function returns the preserved height of window window in pixels. window must be a live window and defaults to the selected one. If the optional argument horizontal is non-
nil, it returns the preserved width of window. It returnsnilif the size of window is not preserved.
This section describes functions for creating a new window by splitting an existing one.
This function creates a new live window next to the window window. If window is omitted or
nil, it defaults to the selected window. That window is split, and reduced in size. The space is taken up by the new window, which is returned.The optional second argument size determines the sizes of window and/or the new window. If it is omitted or
nil, both windows are given equal sizes; if there is an odd line, it is allocated to the new window. If size is a positive number, window is given size lines (or columns, depending on the value of side). If size is a negative number, the new window is given −size lines (or columns).If size is
nil, this function obeys the variableswindow-min-heightandwindow-min-width(see Window Sizes). Thus, it signals an error if splitting would result in making a window smaller than those variables specify. However, a non-nilvalue for size causes those variables to be ignored; in that case, the smallest allowable window is considered to be one that has space for a text area one line tall and/or two columns wide.Hence, if size is specified, it's the caller's responsibility to check whether the emanating windows are large enough to encompass all areas like a mode line or a scroll bar. The function
window-min-size(see Window Sizes) can be used to determine the minimum requirements of window in this regard. Since the new window usually inherits areas like the mode line or the scroll bar from window, that function is also a good guess for the minimum size of the new window. The caller should specify a smaller size only if it correspondingly removes an inherited area before the next redisplay.The optional third argument side determines the position of the new window relative to window. If it is
nilorbelow, the new window is placed below window. If it isabove, the new window is placed above window. In both these cases, size specifies a total window height, in lines.If side is
torright, the new window is placed on the right of window. If side isleft, the new window is placed on the left of window. In both these cases, size specifies a total window width, in columns.The optional fourth argument pixelwise, if non-
nil, means to interpret size in units of pixels, instead of lines and columns.If window is a live window, the new window inherits various properties from it, including margins and scroll bars. If window is an internal window, the new window inherits the properties of the window selected within window's frame.
The behavior of this function may be altered by the window parameters of window, so long as the variable
ignore-window-parametersisnil. If the value of thesplit-windowwindow parameter ist, this function ignores all other window parameters. Otherwise, if the value of thesplit-windowwindow parameter is a function, that function is called with the arguments window, size, and side, in lieu of the usual action ofsplit-window. Otherwise, this function obeys thewindow-atomorwindow-sidewindow parameter, if any. See Window Parameters.
As an example, here is a sequence of split-window calls that
yields the window configuration discussed in Windows and Frames.
This example demonstrates splitting a live window as well as splitting
an internal window. We begin with a frame containing a single window
(a live root window), which we denote by W4. Calling
(split-window W4) yields this window configuration:
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The split-window call has created a new live window, denoted by
W5. It has also created a new internal window, denoted by
W3, which becomes the root window and the parent of both
W4 and W5.
Next, we call (split-window W3 nil 'left), passing the
internal window W3 as the argument. The result:
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A new live window W2 is created, to the left of the internal window W3. A new internal window W1 is created, becoming the new root window.
For interactive use, Emacs provides two commands which always split
the selected window. These call split-window internally.
This function splits the selected window into two side-by-side windows, putting the selected window on the left. If size is positive, the left window gets size columns; if size is negative, the right window gets −size columns.
This function splits the selected window into two windows, one above the other, leaving the upper window selected. If size is positive, the upper window gets size lines; if size is negative, the lower window gets −size lines.
If the value of this variable is non-
nil(the default),split-window-belowbehaves as described above.If it is
nil,split-window-belowadjusts point in each of the two windows to minimize redisplay. (This is useful on slow terminals.) It selects whichever window contains the screen line that point was previously on. Note that this only affectssplit-window-below, not the lower-levelsplit-windowfunction.
Deleting a window removes it from the frame's window tree. If the window is a live window, it disappears from the screen. If the window is an internal window, its child windows are deleted too.
Even after a window is deleted, it continues to exist as a Lisp object, until there are no more references to it. Window deletion can be reversed, by restoring a saved window configuration (see Window Configurations).
This function removes window from display and returns
nil. If window is omitted ornil, it defaults to the selected window. If deleting the window would leave no more windows in the window tree (e.g., if it is the only live window in the frame), an error is signaled.By default, the space taken up by window is given to one of its adjacent sibling windows, if any. However, if the variable
window-combination-resizeis non-nil, the space is proportionally distributed among any remaining windows in the same window combination. See Recombining Windows.The behavior of this function may be altered by the window parameters of window, so long as the variable
ignore-window-parametersisnil. If the value of thedelete-windowwindow parameter ist, this function ignores all other window parameters. Otherwise, if the value of thedelete-windowwindow parameter is a function, that function is called with the argument window, in lieu of the usual action ofdelete-window. Otherwise, this function obeys thewindow-atomorwindow-sidewindow parameter, if any. See Window Parameters.
This function makes window fill its frame, by deleting other windows as necessary. If window is omitted or
nil, it defaults to the selected window. The return value isnil.The behavior of this function may be altered by the window parameters of window, so long as the variable
ignore-window-parametersisnil. If the value of thedelete-other-windowswindow parameter ist, this function ignores all other window parameters. Otherwise, if the value of thedelete-other-windowswindow parameter is a function, that function is called with the argument window, in lieu of the usual action ofdelete-other-windows. Otherwise, this function obeys thewindow-atomorwindow-sidewindow parameter, if any. See Window Parameters.
This function deletes all windows showing buffer-or-name, by calling
delete-windowon those windows. buffer-or-name should be a buffer, or the name of a buffer; if omitted ornil, it defaults to the current buffer. If there are no windows showing the specified buffer, this function does nothing. If the specified buffer is a minibuffer, an error is signaled.If there is a dedicated window showing the buffer, and that window is the only one on its frame, this function also deletes that frame if it is not the only frame on the terminal.
The optional argument frame specifies which frames to operate on:
nilmeans operate on all frames.tmeans operate on the selected frame.visiblemeans operate on all visible frames.0means operate on all visible or iconified frames.- A frame means operate on that frame.
Note that this argument does not have the same meaning as in other functions which scan all live windows (see Cyclic Window Ordering). Specifically, the meanings of
tandnilhere are the opposite of what they are in those other functions.
When deleting the last sibling of a window W, its parent window is deleted too, with W replacing it in the window tree. This means that W must be recombined with its parent's siblings to form a new window combination (see Windows and Frames). In some occasions, deleting a live window may even entail the deletion of two internal windows.
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Deleting W5 in this configuration normally causes the deletion of W3 and W4. The remaining live windows W2, W6 and W7 are recombined to form a new horizontal combination with parent W1.
Sometimes, however, it makes sense to not delete a parent window like W4. In particular, a parent window should not be removed when it was used to preserve a combination embedded in a combination of the same type. Such embeddings make sense to assure that when you split a window and subsequently delete the new window, Emacs reestablishes the layout of the associated frame as it existed before the splitting.
Consider a scenario starting with two live windows W2 and W3 and their parent W1.
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Split W2 to make a new window W4 as follows.
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Now, when enlarging a window vertically, Emacs tries to obtain the corresponding space from its lower sibling, provided such a window exists. In our scenario, enlarging W4 will steal space from W3.
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Deleting W4 will now give its entire space to W2, including the space earlier stolen from W3.
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This can be counterintuitive, in particular if W4 were used for displaying a buffer only temporarily (see Temporary Displays), and you want to continue working with the initial layout.
The behavior can be fixed by making a new parent window when splitting W2. The variable described next allows that to be done.
This variable controls whether splitting a window shall make a new parent window. The following values are recognized:
nil- This means that the new live window is allowed to share the existing parent window, if one exists, provided the split occurs in the same direction as the existing window combination (otherwise, a new internal window is created anyway).
window-size- In this case
display-buffermakes a new parent window if it is passed awindow-heightorwindow-widthentry in the alist argument (see Display Action Functions).
temp-buffer- This value causes the creation of a new parent window when a window is split for showing a temporary buffer (see Temporary Displays) only.
display-buffer- This means that when
display-buffer(see Choosing Window) splits a window it always makes a new parent window.
t- In this case a new parent window is always created when splitting a window. Thus, if the value of this variable is at all times
t, then at all times every window tree is a binary tree (a tree where each window except the root window has exactly one sibling).The default is
nil. Other values are reserved for future use.If, as a consequence of this variable's setting,
split-windowmakes a new parent window, it also callsset-window-combination-limit(see below) on the newly-created internal window. This affects how the window tree is rearranged when the child windows are deleted (see below).
If window-combination-limit is t, splitting W2 in
the initial configuration of our scenario would have produced this:
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A new internal window W5 has been created; its children are W2 and the new live window W4. Now, W2 is the only sibling of W4, so enlarging W4 will try to shrink W2, leaving W3 unaffected. Observe that W5 represents a vertical combination of two windows embedded in the vertical combination W1.
This function sets the combination limit of the window window to limit. This value can be retrieved via the function
window-combination-limit. See below for its effects; note that it is only meaningful for internal windows. Thesplit-windowfunction automatically calls this function, passing ittas limit, provided the value of the variablewindow-combination-limitistwhen it is called.
This function returns the combination limit for window.
The combination limit is meaningful only for an internal window. If it is
nil, then Emacs is allowed to automatically delete window, in response to a window deletion, in order to group the child windows of window with its sibling windows to form a new window combination. If the combination limit ist, the child windows of window are never automatically recombined with its siblings.If, in the configuration shown at the beginning of this section, the combination limit of W4 (the parent window of W6 and W7) is
t, deleting W5 will not implicitly delete W4 too.
Alternatively, the problems sketched above can be avoided by always resizing all windows in the same combination whenever one of its windows is split or deleted. This also permits splitting windows that would be otherwise too small for such an operation.
If this variable is
nil,split-windowcan only split a window (denoted by window) if window's screen area is large enough to accommodate both itself and the new window.If this variable is
t,split-windowtries to resize all windows that are part of the same combination as window, in order to accommodate the new window. In particular, this may allowsplit-windowto succeed even if window is a fixed-size window or too small to ordinarily split. Furthermore, subsequently resizing or deleting window may resize all other windows in its combination.The default is
nil. Other values are reserved for future use. The value of this variable is ignored whenwindow-combination-limitis non-nil.
To illustrate the effect of window-combination-resize, consider
the following frame layout.
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If window-combination-resize is nil, splitting window
W3 leaves the size of W2 unchanged:
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If window-combination-resize is t, splitting W3
instead leaves all three live windows with approximately the same
height:
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Deleting any of the live windows W2, W3 or W4 will distribute its space proportionally among the two remaining live windows.
This function makes window the selected window and the window selected within its frame (see Basic Windows) and selects that frame. It also makes window's buffer (see Buffers and Windows) current and sets that buffer's value of
pointto the value ofwindow-point(see Window Point) in window. window must be a live window. The return value is window.By default, this function also moves window's buffer to the front of the buffer list (see Buffer List), and makes window the most recently selected window. However, if the optional argument norecord is non-
nil, these additional actions are omitted.This function runs
buffer-list-update-hook(see Buffer List) unless norecord is non-nil. Note that applications and internal routines often temporarily select a window in order to simplify coding. As a rule, such selections (including those made by the macrossave-selected-windowandwith-selected-windowbelow) are not recorded thus avoiding to pollutebuffer-list-update-hook. Selections that really count are those causing a visible change in the next redisplay of window's frame and should be always recorded. This also means that to run a function each time a window gets selected, putting it onbuffer-list-update-hookshould be the right choice.
The sequence of calls to select-window with a non-nil
norecord argument determines an ordering of windows by their
selection time. The function get-lru-window can be used to
retrieve the least recently selected live window (see Cyclic Window Ordering).
This macro records the selected frame, as well as the selected window of each frame, executes forms in sequence, then restores the earlier selected frame and windows. It also saves and restores the current buffer. It returns the value of the last form in forms.
This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if forms change them, the change persists. If the previously selected window of some frame is no longer live at the time of exit from forms, that frame's selected window is left alone. If the previously selected window is no longer live, then whatever window is selected at the end of forms remains selected. The current buffer is restored if and only if it is still live when exiting forms.
This macro changes neither the ordering of recently selected windows nor the buffer list.
This macro selects window, executes forms in sequence, then restores the previously selected window and current buffer. The ordering of recently selected windows and the buffer list remain unchanged unless you deliberately change them within forms; for example, by calling
select-windowwith argument norecordnil.This macro does not change the order of recently selected windows or the buffer list.
This function returns the window on frame that is selected within that frame. frame should be a live frame; if omitted or
nil, it defaults to the selected frame.
This function makes window the window selected within the frame frame. frame should be a live frame; if
nil, it defaults to the selected frame. window should be a live window; ifnil, it defaults to the selected window.If frame is the selected frame, this makes window the selected window.
If the optional argument norecord is non-
nil, this function does not alter the list of most recently selected windows, nor the buffer list.
This functions returns the use time of window window. window must be a live window and defaults to the selected one.
The use time of a window is not really a time value, but an integer that does increase monotonically with each call of
select-windowwith anilnorecord argument. The window with the lowest use time is usually called the least recently used window while the window with the highest use time is called the most recently used one (see Cyclic Window Ordering).
When you use the command C-x o (other-window) to select
some other window, it moves through live windows in a specific order.
For any given configuration of windows, this order never varies. It
is called the cyclic ordering of windows.
The ordering is determined by a depth-first traversal of each frame's window tree, retrieving the live windows which are the leaf nodes of the tree (see Windows and Frames). If the minibuffer is active, the minibuffer window is included too. The ordering is cyclic, so the last window in the sequence is followed by the first one.
This function returns a live window, the one following window in the cyclic ordering of windows. window should be a live window; if omitted or
nil, it defaults to the selected window.The optional argument minibuf specifies whether minibuffer windows should be included in the cyclic ordering. Normally, when minibuf is
nil, a minibuffer window is included only if it is currently active; this matches the behavior of C-x o. (Note that a minibuffer window is active as long as its minibuffer is in use; see Minibuffers).If minibuf is
t, the cyclic ordering includes all minibuffer windows. If minibuf is neithertnornil, minibuffer windows are not included even if they are active.The optional argument all-frames specifies which frames to consider:
nilmeans to consider windows on window's frame. If the minibuffer window is considered (as specified by the minibuf argument), then frames that share the minibuffer window are considered too.tmeans to consider windows on all existing frames.visiblemeans to consider windows on all visible frames.- 0 means to consider windows on all visible or iconified frames.
- A frame means to consider windows on that specific frame.
- Anything else means to consider windows on window's frame, and no others.
If more than one frame is considered, the cyclic ordering is obtained by appending the orderings for those frames, in the same order as the list of all live frames (see Finding All Frames).
This function returns a live window, the one preceding window in the cyclic ordering of windows. The other arguments are handled like in
next-window.
This function selects a live window, one count places from the selected window in the cyclic ordering of windows. If count is a positive number, it skips count windows forwards; if count is negative, it skips −count windows backwards; if count is zero, that simply re-selects the selected window. When called interactively, count is the numeric prefix argument.
The optional argument all-frames has the same meaning as in
next-window, like anilminibuf argument tonext-window.This function does not select a window that has a non-
nilno-other-windowwindow parameter (see Window Parameters).
This function calls the function fun once for each live window, with the window as the argument.
It follows the cyclic ordering of windows. The optional arguments minibuf and all-frames specify the set of windows included; these have the same arguments as in
next-window. If all-frames specifies a frame, the first window walked is the first window on that frame (the one returned byframe-first-window), not necessarily the selected window.If fun changes the window configuration by splitting or deleting windows, that does not alter the set of windows walked, which is determined prior to calling fun for the first time.
This function returns
tif the selected window is the only live window, andnilotherwise.If the minibuffer window is active, it is normally considered (so that this function returns
nil). However, if the optional argument no-mini is non-nil, the minibuffer window is ignored even if active. The optional argument all-frames has the same meaning as fornext-window.
The following functions return a window which satisfies some criterion, without selecting it:
This function returns a live window which is heuristically the least recently used. The optional argument all-frames has the same meaning as in
next-window.If any full-width windows are present, only those windows are considered. A minibuffer window is never a candidate. A dedicated window (see Dedicated Windows) is never a candidate unless the optional argument dedicated is non-
nil. The selected window is never returned, unless it is the only candidate. However, if the optional argument not-selected is non-nil, this function returnsnilin that case.
This function is like
get-lru-window, but it returns the most recently used window instead. The meaning of the arguments is the same as described forget-lru-window.
This function returns the window with the largest area (height times width). The optional argument all-frames specifies the windows to search, and has the same meaning as in
next-window.A minibuffer window is never a candidate. A dedicated window (see Dedicated Windows) is never a candidate unless the optional argument dedicated is non-
nil. The selected window is not a candidate if the optional argument not-selected is non-nil. If the optional argument not-selected is non-niland the selected window is the only candidate, this function returnsnil.If there are two candidate windows of the same size, this function prefers the one that comes first in the cyclic ordering of windows, starting from the selected window.
This function calls the function predicate for each of the windows in the cyclic order of windows in turn, passing it the window as an argument. If the predicate returns non-
nilfor any window, this function stops and returns that window. If no such window is found, the return value is default (which defaults tonil).The optional arguments minibuf and all-frames specify the windows to search, and have the same meanings as in
next-window.
This section describes low-level functions for examining and setting the contents of windows. See Switching Buffers, for higher-level functions for displaying a specific buffer in a window.
This function returns the buffer that window is displaying. If window is omitted or
nilit defaults to the selected window. If window is an internal window, this function returnsnil.
This function makes window display buffer-or-name. window should be a live window; if
nil, it defaults to the selected window. buffer-or-name should be a buffer, or the name of an existing buffer. This function does not change which window is selected, nor does it directly change which buffer is current (see Current Buffer). Its return value isnil.If window is strongly dedicated to a buffer and buffer-or-name does not specify that buffer, this function signals an error. See Dedicated Windows.
By default, this function resets window's position, display margins, fringe widths, and scroll bar settings, based on the local variables in the specified buffer. However, if the optional argument keep-margins is non-
nil, it leaves the display margins and fringe widths unchanged.When writing an application, you should normally use the higher-level functions described in Switching Buffers, instead of calling
set-window-bufferdirectly.This runs
window-scroll-functions, followed bywindow-configuration-change-hook. See Window Hooks.
This buffer-local variable records the number of times a buffer has been displayed in a window. It is incremented each time
set-window-bufferis called for the buffer.
This buffer-local variable records the time at which a buffer was last displayed in a window. The value is
nilif the buffer has never been displayed. It is updated each timeset-window-bufferis called for the buffer, with the value returned bycurrent-time(see Time of Day).
This function returns the first window displaying buffer-or-name in the cyclic ordering of windows, starting from the selected window (see Cyclic Window Ordering). If no such window exists, the return value is
nil.buffer-or-name should be a buffer or the name of a buffer; if omitted or
nil, it defaults to the current buffer. The optional argument all-frames specifies which windows to consider:
tmeans consider windows on all existing frames.visiblemeans consider windows on all visible frames.- 0 means consider windows on all visible or iconified frames.
- A frame means consider windows on that frame only.
- Any other value means consider windows on the selected frame.
Note that these meanings differ slightly from those of the all-frames argument to
next-window(see Cyclic Window Ordering). This function may be changed in a future version of Emacs to eliminate this discrepancy.
This function returns a list of all windows currently displaying buffer-or-name. buffer-or-name should be a buffer or the name of an existing buffer. If omitted or
nil, it defaults to the current buffer. If the currently selected window displays buffer-or-name, it will be the first in the list returned by this function.The arguments minibuf and all-frames have the same meanings as in the function
next-window(see Cyclic Window Ordering). Note that the all-frames argument does not behave exactly like inget-buffer-window.
This command replaces buffer-or-name with some other buffer, in all windows displaying it. buffer-or-name should be a buffer, or the name of an existing buffer; if omitted or
nil, it defaults to the current buffer.The replacement buffer in each window is chosen via
switch-to-prev-buffer(see Window History). Any dedicated window displaying buffer-or-name is deleted if possible (see Dedicated Windows). If such a window is the only window on its frame and there are other frames on the same terminal, the frame is deleted as well. If the dedicated window is the only window on the only frame on its terminal, the buffer is replaced anyway.
This section describes high-level functions for switching to a specified buffer in some window. In general, “switching to a buffer” means to (1) show the buffer in some window, (2) make that window the selected window (and its frame the selected frame), and (3) make the buffer the current buffer.
Do not use these functions to make a buffer temporarily
current just so a Lisp program can access or modify it. They have
side-effects, such as changing window histories (see Window History), which will surprise the user if used that way. If you want
to make a buffer current to modify it in Lisp, use
with-current-buffer, save-current-buffer, or
set-buffer. See Current Buffer.
This command attempts to display buffer-or-name in the selected window and make it the current buffer. It is often used interactively (as the binding of C-x b), as well as in Lisp programs. The return value is the buffer switched to.
If buffer-or-name is
nil, it defaults to the buffer returned byother-buffer(see Buffer List). If buffer-or-name is a string that is not the name of any existing buffer, this function creates a new buffer with that name; the new buffer's major mode is determined by the variablemajor-mode(see Major Modes).Normally, the specified buffer is put at the front of the buffer list—both the global buffer list and the selected frame's buffer list (see Buffer List). However, this is not done if the optional argument norecord is non-
nil.Sometimes, the selected window may not be suitable for displaying the buffer. This happens if the selected window is a minibuffer window, or if the selected window is strongly dedicated to its buffer (see Dedicated Windows). In such cases, the command normally tries to display the buffer in some other window, by invoking
pop-to-buffer(see below).If the optional argument force-same-window is non-
niland the selected window is not suitable for displaying the buffer, this function always signals an error when called non-interactively. In interactive use, if the selected window is a minibuffer window, this function will try to use some other window instead. If the selected window is strongly dedicated to its buffer, the optionswitch-to-buffer-in-dedicated-windowdescribed next can be used to proceed.
This option, if non-
nil, allowsswitch-to-bufferto proceed when called interactively and the selected window is strongly dedicated to its buffer.The following values are respected:
nil- Disallows switching and signals an error as in non-interactive use.
prompt- Prompts the user whether to allow switching.
pop- Invokes
pop-to-bufferto proceed.
t- Marks the selected window as non-dedicated and proceeds.
This option does not affect non-interactive calls of
switch-to-buffer.
By default, switch-to-buffer shows the buffer at its position of
point. This behavior can be tuned using the following option.
If this variable is
nil,switch-to-bufferdisplays the buffer specified by buffer-or-name at the position of that buffer'spoint. If this variable isalready-displayed, it tries to display the buffer at its previous position in the selected window, provided the buffer is currently displayed in some other window on any visible or iconified frame. If this variable ist,switch-to-bufferunconditionally tries to display the buffer at its previous position in the selected window.This variable is ignored if the buffer is already displayed in the selected window or never appeared in it before, or if
switch-to-buffercallspop-to-bufferto display the buffer.
The next two commands are similar to switch-to-buffer, except for
the described features.
This function displays the buffer specified by buffer-or-name in some window other than the selected window. It uses the function
pop-to-bufferinternally (see below).If the selected window already displays the specified buffer, it continues to do so, but another window is nonetheless found to display it as well.
The buffer-or-name and norecord arguments have the same meanings as in
switch-to-buffer.
This function displays the buffer specified by buffer-or-name in a new frame. It uses the function
pop-to-bufferinternally (see below).If the specified buffer is already displayed in another window, in any frame on the current terminal, this switches to that window instead of creating a new frame. However, the selected window is never used for this.
The buffer-or-name and norecord arguments have the same meanings as in
switch-to-buffer.
The above commands use the function pop-to-buffer, which
flexibly displays a buffer in some window and selects that window for
editing. In turn, pop-to-buffer uses display-buffer for
displaying the buffer. Hence, all the variables affecting
display-buffer will affect it as well. See Choosing Window,
for the documentation of display-buffer.
This function makes buffer-or-name the current buffer and displays it in some window, preferably not the window currently selected. It then selects the displaying window. If that window is on a different graphical frame, that frame is given input focus if possible (see Input Focus). The return value is the buffer that was switched to.
If buffer-or-name is
nil, it defaults to the buffer returned byother-buffer(see Buffer List). If buffer-or-name is a string that is not the name of any existing buffer, this function creates a new buffer with that name; the new buffer's major mode is determined by the variablemajor-mode(see Major Modes).If action is non-
nil, it should be a display action to pass todisplay-buffer(see Choosing Window). Alternatively, a non-nil, non-list value means to pop to a window other than the selected one—even if the buffer is already displayed in the selected window.Like
switch-to-buffer, this function updates the buffer list unless norecord is non-nil.
The command display-buffer flexibly chooses a window for
display, and displays a specified buffer in that window. It can be
called interactively, via the key binding C-x 4 C-o. It is also
used as a subroutine by many functions and commands, including
switch-to-buffer and pop-to-buffer (see Switching Buffers).
This command performs several complex steps to find a window to
display in. These steps are described by means of display
actions, which have the form (function . alist).
Here, function is either a function or a list of functions,
which we refer to as action functions; alist is an
association list, which we refer to as an action alist.
An action function accepts two arguments: the buffer to display and
an action alist. It attempts to display the buffer in some window,
picking or creating a window according to its own criteria. If
successful, it returns the window; otherwise, it returns nil.
See Display Action Functions, for a list of predefined action
functions.
display-buffer works by combining display actions from
several sources, and calling the action functions in turn, until one
of them manages to display the buffer and returns a non-nil
value.
This command makes buffer-or-name appear in some window, without selecting the window or making the buffer current. The argument buffer-or-name must be a buffer or the name of an existing buffer. The return value is the window chosen to display the buffer.
The optional argument action, if non-
nil, should normally be a display action (described above).display-bufferbuilds a list of action functions and an action alist, by consolidating display actions from the following sources (in order):
- The variable
display-buffer-overriding-action.- The user option
display-buffer-alist.- The action argument.
- The user option
display-buffer-base-action.- The constant
display-buffer-fallback-action.Each action function is called in turn, passing the buffer as the first argument and the combined action alist as the second argument, until one of the functions returns non-
nil. The caller can pass(allow-no-window . t)as an element of the action alist to indicate its readiness to handle the case of not displaying the buffer in a window.The argument action can also have a non-
nil, non-list value. This has the special meaning that the buffer should be displayed in a window other than the selected one, even if the selected window is already displaying it. If called interactively with a prefix argument, action ist.The optional argument frame, if non-
nil, specifies which frames to check when deciding whether the buffer is already displayed. It is equivalent to adding an element(reusable-frames .frame)to the action alist of action. See Display Action Functions.
The value of this variable should be a display action, which is treated with the highest priority by
display-buffer. The default value is empty, i.e.,(nil . nil).
The value of this option is an alist mapping conditions to display actions. Each condition may be either a regular expression matching a buffer name or a function that takes two arguments: a buffer name and the action argument passed to
display-buffer. If the name of the buffer passed todisplay-buffereither matches a regular expression in this alist or the function specified by a condition returns non-nil, thendisplay-bufferuses the corresponding display action to display the buffer.
The value of this option should be a display action. This option can be used to define a standard display action for calls to
display-buffer.
This display action specifies the fallback behavior for
display-bufferif no other display actions are given.
display-buffer
The following basic action functions are defined in Emacs. Each of
these functions takes two arguments: buffer, the buffer to
display, and alist, an action alist. Each action function
returns the window if it succeeds, and nil if it fails.
This function tries to display buffer in the selected window. It fails if the selected window is a minibuffer window or is dedicated to another buffer (see Dedicated Windows). It also fails if alist has a non-
nilinhibit-same-windowentry.
This function tries to display buffer by finding a window that is already displaying it.
If alist has a non-
nilinhibit-same-windowentry, the selected window is not eligible for reuse. If alist contains areusable-framesentry, its value determines which frames to search for a reusable window:
nilmeans consider windows on the selected frame. (Actually, the last non-minibuffer frame.)tmeans consider windows on all frames.visiblemeans consider windows on all visible frames.- 0 means consider windows on all visible or iconified frames.
- A frame means consider windows on that frame only.
Note that these meanings differ slightly from those of the all-frames argument to
next-window(see Cyclic Window Ordering).If alist contains no
reusable-framesentry, this function normally searches just the selected frame; however, if the variablepop-up-framesis non-nil, it searches all frames on the current terminal. See Choosing Window Options.If this function chooses a window on another frame, it makes that frame visible and, unless alist contains an
inhibit-switch-frameentry (see Choosing Window Options), raises that frame if necessary.
This function creates a new frame, and displays the buffer in that frame's window. It actually performs the frame creation by calling the function specified in
pop-up-frame-function(see Choosing Window Options). If alist contains apop-up-frame-parametersentry, the associated value is added to the newly created frame's parameters.
This function tries to display buffer by trying to find a frame that meets a predicate (by default any frame other than the current frame).
If this function chooses a window on another frame, it makes that frame visible and, unless alist contains an
inhibit-switch-frameentry (see Choosing Window Options), raises that frame if necessary.If alist has a non-
nilframe-predicateentry, its value is a function taking one argument (a frame), returning non-nilif the frame is a candidate; this function replaces the default predicate.If alist has a non-
nilinhibit-same-windowentry, the selected window is used; thus if the selected frame has a single window, it is not used.
This function tries to display buffer by splitting the largest or least recently-used window (typically one on the selected frame). It actually performs the split by calling the function specified in
split-window-preferred-function(see Choosing Window Options).The size of the new window can be adjusted by supplying
window-heightandwindow-widthentries in alist. To adjust the window's height, use an entry whose car iswindow-heightand whose cdr is one of:
nilmeans to leave the height of the new window alone.- A number specifies the desired height of the new window. An integer specifies the number of lines of the window. A floating-point number gives the fraction of the window's height with respect to the height of the frame's root window.
- If the cdr specifies a function, that function is called with one argument: the new window. The function is supposed to adjust the height of the window; its return value is ignored. Suitable functions are
shrink-window-if-larger-than-bufferandfit-window-to-buffer, see Resizing Windows.To adjust the window's width, use an entry whose car is
window-widthand whose cdr is one of:
nilmeans to leave the width of the new window alone.- A number specifies the desired width of the new window. An integer specifies the number of columns of the window. A floating-point number gives the fraction of the window's width with respect to the width of the frame's root window.
- If the cdr specifies a function, that function is called with one argument: the new window. The function is supposed to adjust the width of the window; its return value is ignored.
If alist contains a
preserve-sizeentry, Emacs will try to preserve the size of the new window during future resize operations (see Preserving Window Sizes). The cdr of that entry must be a cons cell whose car, if non-nil, means to preserve the width of the window and whose cdr, if non-nil, means to preserve the height of the window.This function can fail if no window splitting can be performed for some reason (e.g., if the selected frame has an
unsplittableframe parameter; see Buffer Parameters).
This function tries to display buffer in a window below the selected window. This means to either split the selected window or use the window below the selected one. If it does create a new window, it will also adjust its size provided alist contains a suitable
window-heightorwindow-widthentry, see above.
This function tries to display buffer in a window previously showing it. If alist has a non-
nilinhibit-same-windowentry, the selected window is not eligible for reuse. If alist contains areusable-framesentry, its value determines which frames to search for a suitable window as withdisplay-buffer-reuse-window.If alist has a
previous-windowentry, the window specified by that entry will override any other window found by the methods above, even if that window never showed buffer before.
This function tries to display buffer in a window at the bottom of the selected frame.
This either splits the window at the bottom of the frame or the frame's root window, or reuses an existing window at the bottom of the selected frame.
This function tries to display buffer by choosing an existing window and displaying the buffer in that window. It can fail if all windows are dedicated to another buffer (see Dedicated Windows).
If alist has a non-
nilallow-no-windowentry, then this function does not displaybuffer. This allows you to override the default action and avoid displaying the buffer. It is assumed that when the caller specifies a non-nilallow-no-windowvalue it can handle anilvalue returned fromdisplay-bufferin this case.
To illustrate the use of action functions, consider the following example.
(display-buffer
(get-buffer-create "*foo*")
'((display-buffer-reuse-window
display-buffer-pop-up-window
display-buffer-pop-up-frame)
(reusable-frames . 0)
(window-height . 10) (window-width . 40)))
Evaluating the form above will cause display-buffer to proceed as
follows: If a buffer called *foo* already appears on a visible or
iconified frame, it will reuse its window. Otherwise, it will try to
pop up a new window or, if that is impossible, a new frame and show the
buffer there. If all these steps fail, it will proceed using whatever
display-buffer-base-action and
display-buffer-fallback-action prescribe.
Furthermore, display-buffer will try to adjust a reused window
(provided *foo* was put by display-buffer there before) or a
popped-up window as follows: If the window is part of a vertical
combination, it will set its height to ten lines. Note that if, instead
of the number 10, we specified the function
fit-window-to-buffer, display-buffer would come up with a
one-line window to fit the empty buffer. If the window is part of a
horizontal combination, it sets its width to 40 columns. Whether a new
window is vertically or horizontally combined depends on the shape of
the window split and the values of
split-window-preferred-function, split-height-threshold
and split-width-threshold (see Choosing Window Options).
Now suppose we combine this call with a preexisting setup for
display-buffer-alist as follows.
(let ((display-buffer-alist
(cons
'("\\*foo\\*"
(display-buffer-reuse-window display-buffer-below-selected)
(reusable-frames)
(window-height . 5))
display-buffer-alist)))
(display-buffer
(get-buffer-create "*foo*")
'((display-buffer-reuse-window
display-buffer-pop-up-window
display-buffer-pop-up-frame)
(reusable-frames . 0)
(window-height . 10) (window-width . 40))))
This form will have display-buffer first try reusing a window
that shows *foo* on the selected frame. If there's no such window, it
will try to split the selected window or, if that is impossible, use the
window below the selected window.
If there's no window below the selected one, or the window below the
selected one is dedicated to its buffer, display-buffer will
proceed as described in the previous example. Note, however, that when
it tries to adjust the height of any reused or popped-up window, it will
in any case try to set its number of lines to 5 since that value
overrides the corresponding specification in the action argument
of display-buffer.
The behavior of the standard display actions of display-buffer
(see Choosing Window) can be modified by a variety of user
options.
If the value of this variable is non-
nil,display-bufferis allowed to split an existing window to make a new window for displaying in. This is the default.This variable is provided mainly for backward compatibility. It is obeyed by
display-buffervia a special mechanism indisplay-buffer-fallback-action, which only calls the action functiondisplay-buffer-pop-up-window(see Display Action Functions) when the value isnil. It is not consulted bydisplay-buffer-pop-up-windowitself, which the user may specify directly indisplay-buffer-alistetc.
This variable specifies a function for splitting a window, in order to make a new window for displaying a buffer. It is used by the
display-buffer-pop-up-windowaction function to actually split the window (see Display Action Functions).The default value is
split-window-sensibly, which is documented below. The value must be a function that takes one argument, a window, and return either a new window (which will be used to display the desired buffer) ornil(which means the splitting failed).
This function tries to split window, and return the newly created window. If window cannot be split, it returns
nil. If window is omitted ornil, it defaults to the selected window.This function obeys the usual rules that determine when a window may be split (see Splitting Windows). It first tries to split by placing the new window below, subject to the restriction imposed by
split-height-threshold(see below), in addition to any other restrictions. If that fails, it tries to split by placing the new window to the right, subject tosplit-width-threshold(see below). If that fails, and the window is the only window on its frame, this function again tries to split and place the new window below, disregardingsplit-height-threshold. If this fails as well, this function gives up and returnsnil.
This variable, used by
split-window-sensibly, specifies whether to split the window placing the new window below. If it is an integer, that means to split only if the original window has at least that many lines. If it isnil, that means not to split this way.
This variable, used by
split-window-sensibly, specifies whether to split the window placing the new window to the right. If the value is an integer, that means to split only if the original window has at least that many columns. If the value isnil, that means not to split this way.
This variable, if non-
nil, causesdisplay-bufferto even window sizes whenever it reuses an existing window and that window is adjacent to the selected one.If its value is
width-only, sizes are evened only if the reused window is on the left or right of the selected one and the selected window is wider than the reused one. If its value isheight-onlysizes are evened only if the reused window is above or beneath the selected window and the selected window is higher than the reused one. Any other non-nilvalue means to even sizes in any of these cases provided the selected window is larger than the reused one in the sense of their combination.
If the value of this variable is non-
nil, that meansdisplay-buffermay display buffers by making new frames. The default isnil.A non-
nilvalue also means that whendisplay-bufferis looking for a window already displaying buffer-or-name, it can search any visible or iconified frame, not just the selected frame.This variable is provided mainly for backward compatibility. It is obeyed by
display-buffervia a special mechanism indisplay-buffer-fallback-action, which calls the action functiondisplay-buffer-pop-up-frame(see Display Action Functions) if the value is non-nil. (This is done before attempting to split a window.) This variable is not consulted bydisplay-buffer-pop-up-frameitself, which the user may specify directly indisplay-buffer-alistetc.
This variable specifies a function for creating a new frame, in order to make a new window for displaying a buffer. It is used by the
display-buffer-pop-up-frameaction function (see Display Action Functions).The value should be a function that takes no arguments and returns a frame, or
nilif no frame could be created. The default value is a function that creates a frame using the parameters specified bypop-up-frame-alist(see below).
This variable holds an alist of frame parameters (see Frame Parameters), which is used by the default function in
pop-up-frame-functionto make a new frame. The default isnil.
A list of buffer names for buffers that should be displayed in the selected window. If a buffer's name is in this list,
display-bufferhandles the buffer by showing it in the selected window.
A list of regular expressions that specify buffers that should be displayed in the selected window. If the buffer's name matches any of the regular expressions in this list,
display-bufferhandles the buffer by showing it in the selected window.
This function returns
tif displaying a buffer named buffer-name withdisplay-bufferwould put it in the selected window.
Each window remembers in a list the buffers it has previously displayed,
and the order in which these buffers were removed from it. This history
is used, for example, by replace-buffer-in-windows
(see Buffers and Windows). The list is automatically maintained by
Emacs, but you can use the following functions to explicitly inspect or
alter it:
This function returns a list specifying the previous contents of window. The optional argument window should be a live window and defaults to the selected one.
Each list element has the form
(buffer window-start window-pos), where buffer is a buffer previously shown in the window, window-start is the window start position (see Window Start and End) when that buffer was last shown, and window-pos is the point position (see Window Point) when that buffer was last shown in window.The list is ordered so that earlier elements correspond to more recently-shown buffers, and the first element usually corresponds to the buffer most recently removed from the window.
This function sets window's previous buffers to the value of prev-buffers. The argument window must be a live window and defaults to the selected one. The argument prev-buffers should be a list of the same form as that returned by
window-prev-buffers.
In addition, each buffer maintains a list of next buffers, which
is a list of buffers re-shown by switch-to-prev-buffer (see
below). This list is mainly used by switch-to-prev-buffer and
switch-to-next-buffer for choosing buffers to switch to.
This function returns the list of buffers recently re-shown in window via
switch-to-prev-buffer. The window argument must denote a live window ornil(meaning the selected window).
This function sets the next buffer list of window to next-buffers. The window argument should be a live window or
nil(meaning the selected window). The argument next-buffers should be a list of buffers.
The following commands can be used to cycle through the global buffer
list, much like bury-buffer and unbury-buffer. However,
they cycle according to the specified window's history list, rather
than the global buffer list. In addition, they restore
window-specific window start and point positions, and may show a
buffer even if it is already shown in another window. The
switch-to-prev-buffer command, in particular, is used by
replace-buffer-in-windows, bury-buffer and
quit-window to find a replacement buffer for a window.
This command displays the previous buffer in window. The argument window should be a live window or
nil(meaning the selected window). If the optional argument bury-or-kill is non-nil, this means that the buffer currently shown in window is about to be buried or killed and consequently should not be switched to in future invocations of this command.The previous buffer is usually the buffer shown before the buffer currently shown in window. However, a buffer that has been buried or killed, or has been already shown by a recent invocation of
switch-to-prev-buffer, does not qualify as previous buffer.If repeated invocations of this command have already shown all buffers previously shown in window, further invocations will show buffers from the buffer list of the frame window appears on (see Buffer List), trying to skip buffers that are already shown in another window on that frame.
This command switches to the next buffer in window, thus undoing the effect of the last
switch-to-prev-buffercommand in window. The argument window must be a live window and defaults to the selected one.If there is no recent invocation of
switch-to-prev-bufferthat can be undone, this function tries to show a buffer from the buffer list of the frame window appears on (see Buffer List).
By default switch-to-prev-buffer and switch-to-next-buffer
can switch to a buffer that is already shown in another window on the
same frame. The following option can be used to override this behavior.
If this variable is non-
nil,switch-to-prev-bufferandswitch-to-next-buffermay switch to a buffer that is already visible on the same frame, provided the buffer was shown in the relevant window before. If it isnil,switch-to-prev-bufferandswitch-to-next-bufferalways try to avoid switching to a buffer that is already visible in another window on the same frame. The default ist.
Functions for displaying a buffer can be told to not use specific
windows by marking these windows as dedicated to their buffers.
display-buffer (see Choosing Window) never uses a dedicated
window for displaying another buffer in it. get-lru-window and
get-largest-window (see Cyclic Window Ordering) do not
consider dedicated windows as candidates when their dedicated
argument is non-nil. The behavior of set-window-buffer
(see Buffers and Windows) with respect to dedicated windows is
slightly different, see below.
Functions supposed to remove a buffer from a window or a window from a frame can behave specially when a window they operate on is dedicated. We will distinguish three basic cases, namely where (1) the window is not the only window on its frame, (2) the window is the only window on its frame but there are other frames on the same terminal left, and (3) the window is the only window on the only frame on the same terminal.
In particular, delete-windows-on (see Deleting Windows)
handles case (2) by deleting the associated frame and case (3) by
showing another buffer in that frame's only window. The function
replace-buffer-in-windows (see Buffers and Windows) which is
called when a buffer gets killed, deletes the window in case (1) and
behaves like delete-windows-on otherwise.
When bury-buffer (see Buffer List) operates on the
selected window (which shows the buffer that shall be buried), it
handles case (2) by calling frame-auto-hide-function
(see Quitting Windows) to deal with the selected frame. The other
two cases are handled as with replace-buffer-in-windows.
This function returns non-
nilif window is dedicated to its buffer andnilotherwise. More precisely, the return value is the value assigned by the last call ofset-window-dedicated-pfor window, ornilif that function was never called with window as its argument. The default for window is the selected window.
This function marks window as dedicated to its buffer if flag is non-
nil, and non-dedicated otherwise.As a special case, if flag is
t, window becomes strongly dedicated to its buffer.set-window-buffersignals an error when the window it acts upon is strongly dedicated to its buffer and does not already display the buffer it is asked to display. Other functions do not treattdifferently from any non-nilvalue.
When you want to get rid of a window used for displaying a buffer, you
can call delete-window or delete-windows-on
(see Deleting Windows) to remove that window from its frame. If the
buffer is shown on a separate frame, you might want to call
delete-frame (see Deleting Frames) instead. If, on the other
hand, a window has been reused for displaying the buffer, you might
prefer showing the buffer previously shown in that window, by calling the
function switch-to-prev-buffer (see Window History).
Finally, you might want to either bury (see Buffer List) or kill
(see Killing Buffers) the window's buffer.
The following command uses information on how the window for displaying the buffer was obtained in the first place, thus attempting to automate the above decisions for you.
This command quits window and buries its buffer. The argument window must be a live window and defaults to the selected one. With prefix argument kill non-
nil, it kills the buffer instead of burying it. It calls the functionquit-restore-windowdescribed next to deal with the window and its buffer.
This function tries to restore the state of window that existed before its buffer was displayed in it. The optional argument window must be a live window and defaults to the selected one.
If window was created specially for displaying its buffer, this function deletes window provided its frame contains at least one other live window. If window is the only window on its frame and there are other frames on the frame's terminal, the value of the optional argument bury-or-kill determines how to proceed with the window. If bury-or-kill equals
kill, the frame is deleted unconditionally. Otherwise, the fate of the frame is determined by callingframe-auto-hide-function(see below) with that frame as sole argument.Otherwise, this function tries to redisplay the buffer previously shown in window. It also tries to restore the window start (see Window Start and End) and point (see Window Point) positions of the previously shown buffer. If, in addition, window's buffer was temporarily resized, this function will also try to restore the original height of window.
The cases described so far require that the buffer shown in window is still the buffer displayed by the last buffer display function for this window. If another buffer has been shown in the meantime, or the buffer previously shown no longer exists, this function calls
switch-to-prev-buffer(see Window History) to show some other buffer instead.The optional argument bury-or-kill specifies how to deal with window's buffer. The following values are handled:
nil- This means to not deal with the buffer in any particular way. As a consequence, if window is not deleted, invoking
switch-to-prev-bufferwill usually show the buffer again.
append- This means that if window is not deleted, its buffer is moved to the end of window's list of previous buffers, so it's less likely that a future invocation of
switch-to-prev-bufferwill switch to it. Also, it moves the buffer to the end of the frame's buffer list.
bury- This means that if window is not deleted, its buffer is removed from window's list of previous buffers. Also, it moves the buffer to the end of the frame's buffer list. This value provides the most reliable remedy to not have
switch-to-prev-bufferswitch to this buffer again without killing the buffer.
kill- This means to kill window's buffer.
quit-restore-windowbases its decisions on information stored in window'squit-restorewindow parameter (see Window Parameters), and resets that parameter tonilafter it's done.
The following option specifies how to deal with a frame containing just one window that should be either quit, or whose buffer should be buried.
The function specified by this option is called to automatically hide frames. This function is called with one argument—a frame.
The function specified here is called by
bury-buffer(see Buffer List) when the selected window is dedicated and shows the buffer to bury. It is also called byquit-restore-window(see above) when the frame of the window to quit has been specially created for displaying that window's buffer and the buffer is not killed.The default is to call
iconify-frame(see Visibility of Frames). Alternatively, you may specify eitherdelete-frame(see Deleting Frames) to remove the frame from its display,ignoreto leave the frame unchanged, or any other function that can take a frame as its sole argument.Note that the function specified by this option is called only if the specified frame contains just one live window and there is at least one other frame on the same terminal.
Each window has its own value of point (see Point), independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.
As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.
This function returns the current position of point in window. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected. The default for window is the selected window.
When window is the selected window, the value returned is the value of point in that window's buffer. Strictly speaking, it would be more correct to return the top-level value of point, outside of any
save-excursionforms. But that value is hard to find.
This function positions point in window at position position in window's buffer. It returns position.
If window is selected, this simply does
goto-charin window's buffer.
This variable specifies the marker insertion type (see Marker Insertion Types) of
window-point. The default isnil, sowindow-pointwill stay behind text inserted there.
Each window maintains a marker used to keep track of a buffer position that specifies where in the buffer display should start. This position is called the display-start position of the window (or just the start). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line.
After switching windows or buffers, and in some other cases, if the window start is in the middle of a line, Emacs adjusts the window start to the start of a line. This prevents certain operations from leaving the window start at a meaningless point within a line. This feature may interfere with testing some Lisp code by executing it using the commands of Lisp mode, because they trigger this readjustment. To test such code, put it into a command and bind the command to a key.
This function returns the display-start position of window window. If window is
nil, the selected window is used.When you create a window, or display a different buffer in it, the display-start position is set to a display-start position recently used for the same buffer, or to
point-minif the buffer doesn't have any.Redisplay updates the window-start position (if you have not specified it explicitly since the previous redisplay)—to make sure point appears on the screen. Nothing except redisplay automatically changes the window-start position; if you move point, do not expect the window-start position to change in response until after the next redisplay.
This function is like
window-start, except that when window is a part of a group of windows (see Window Group),window-group-startreturns the start position of the entire group. This condition holds when the buffer local variablewindow-group-start-functionis set to a function. In this case,window-group-startcalls the function with the single argument window, then returns its result.
This function returns the position where display of its buffer ends in window. The default for window is the selected window.
Simply changing the buffer text or moving point does not update the value that
window-endreturns. The value is updated only when Emacs redisplays and redisplay completes without being preempted.If the last redisplay of window was preempted, and did not finish, Emacs does not know the position of the end of display in that window. In that case, this function returns
nil.If update is non-
nil,window-endalways returns an up-to-date value for where display ends, based on the currentwindow-startvalue. If a previously saved value of that position is still valid,window-endreturns that value; otherwise it computes the correct value by scanning the buffer text.Even if update is non-
nil,window-enddoes not attempt to scroll the display if point has moved off the screen, the way real redisplay would do. It does not alter thewindow-startvalue. In effect, it reports where the displayed text will end if scrolling is not required.
This function is like
window-end, except that when window is a part of a group of windows (see Window Group),window-group-endreturns the end position of the entire group. This condition holds when the buffer local variablewindow-group-end-functionis set to a function. In this case,window-group-endcalls the function with the two arguments window and update, then returns its result. The argument update has the same meaning as inwindow-end.
This function sets the display-start position of window to position in window's buffer. It returns position.
The display routines insist that the position of point be visible when a buffer is displayed. Normally, they change the display-start position (that is, scroll the window) whenever necessary to make point visible. However, if you specify the start position with this function using
nilfor noforce, it means you want display to start at position even if that would put the location of point off the screen. If this does place point off screen, the display routines move point to the left margin on the middle line in the window.For example, if point is 1 and you set the start of the window to 37, the start of the next line, point will be above the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example:
;; Here is what `foo' looks like before executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (save-excursion (goto-char 1) (forward-line 1) (point))) => 37 ;; Here is what `foo' looks like after executing ;; theset-window-startexpression. ---------- Buffer: foo ---------- 2 3 -!-4 5 6 ---------- Buffer: foo ----------If noforce is non-
nil, and position would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus position is not used.
This function is like
set-window-start, except that when window is a part of a group of windows (see Window Group),set-window-group-startsets the start position of the entire group. This condition holds when the buffer local variableset-window-group-start-functionis set to a function. In this case,set-window-group-startcalls the function with the three arguments window, position, and noforce, then returns its result. The arguments position and noforce in this function have the same meaning as inset-window-start.
This function returns non-
nilif position is within the range of text currently visible on the screen in window. It returnsnilif position is scrolled vertically out of view. Locations that are partially obscured are not considered visible unless partially is non-nil. The argument position defaults to the current position of point in window; window defaults to the selected window. If position ist, that means to check either the first visible position of the last screen line in window, or the end-of-buffer position, whichever comes first.This function considers only vertical scrolling. If position is out of view only because window has been scrolled horizontally,
pos-visible-in-window-preturns non-nilanyway. See Horizontal Scrolling.If position is visible,
pos-visible-in-window-preturnstif partially isnil; if partially is non-nil, and the character following position is fully visible, it returns a list of the form(x y), where x and y are the pixel coordinates relative to the top left corner of the window; otherwise it returns an extended list of the form(x y rtop rbot rowh vpos), where rtop and rbot specify the number of off-window pixels at the top and bottom of the row at position, rowh specifies the visible height of that row, and vpos specifies the vertical position (zero-based row number) of that row.Here is an example:
;; If point is off the screen now, recenter it now. (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0))
This function is like
pos-visible-in-window-p, except that when window is a part of a group of windows (see Window Group),pos-visible-in-window-group-ptests the visibility of pos in the entire group, not just in the single window. This condition holds when the buffer local variablepos-visible-in-window-group-p-functionis set to a function. In this casepos-visible-in-window-group-pcalls the function with the three arguments position, window, and partially, then returns its result. The arguments position and partially have the same meaning as inpos-visible-in-window-p.
This function returns the height of text line line in window. If line is one of
header-lineormode-line,window-line-heightreturns information about the corresponding line of the window. Otherwise, line is a text line number starting from 0. A negative number counts from the end of the window. The default for line is the current line in window; the default for window is the selected window.If the display is not up to date,
window-line-heightreturnsnil. In that case,pos-visible-in-window-pmay be used to obtain related information.If there is no line corresponding to the specified line,
window-line-heightreturnsnil. Otherwise, it returns a list(height vpos ypos offbot), where height is the height in pixels of the visible part of the line, vpos and ypos are the vertical position in lines and pixels of the line relative to the top of the first text line, and offbot is the number of off-window pixels at the bottom of the text line. If there are off-window pixels at the top of the (first) text line, ypos is negative.
Textual scrolling means moving the text up or down through a
window. It works by changing the window's display-start location. It
may also change the value of window-point to keep point on the
screen (see Window Point).
The basic textual scrolling functions are scroll-up (which
scrolls forward) and scroll-down (which scrolls backward). In
these function names, “up” and “down” refer to the direction of
motion of the buffer text relative to the window. Imagine that the
text is written on a long roll of paper and that the scrolling
commands move the paper up and down. Thus, if you are looking at the
middle of a buffer and repeatedly call scroll-down, you will
eventually see the beginning of the buffer.
Unfortunately, this sometimes causes confusion, because some people tend to think in terms of the opposite convention: they imagine the window moving over text that remains in place, so that “down” commands take you to the end of the buffer. This convention is consistent with fact that such a command is bound to a key named <PageDown> on modern keyboards.
Textual scrolling functions (aside from scroll-other-window)
have unpredictable results if the current buffer is not the one
displayed in the selected window. See Current Buffer.
If the window contains a row taller than the height of the window
(for example in the presence of a large image), the scroll functions
will adjust the window's vertical scroll position to scroll the
partially visible row. Lisp callers can disable this feature by
binding the variable auto-window-vscroll to nil
(see Vertical Scrolling).
This function scrolls forward by count lines in the selected window.
If count is negative, it scrolls backward instead. If count is
nil(or omitted), the distance scrolled isnext-screen-context-lineslines less than the height of the window's text area.If the selected window cannot be scrolled any further, this function signals an error. Otherwise, it returns
nil.
This function scrolls backward by count lines in the selected window.
If count is negative, it scrolls forward instead. In other respects, it behaves the same way as
scroll-updoes.
This behaves like
scroll-up, except that if the selected window cannot be scrolled any further and the value of the variablescroll-error-top-bottomist, it tries to move to the end of the buffer instead. If point is already there, it signals an error.
This behaves like
scroll-down, except that if the selected window cannot be scrolled any further and the value of the variablescroll-error-top-bottomist, it tries to move to the beginning of the buffer instead. If point is already there, it signals an error.
This function scrolls the text in another window upward count lines. Negative values of count, or
nil, are handled as inscroll-up.You can specify which buffer to scroll by setting the variable
other-window-scroll-bufferto a buffer. If that buffer isn't already displayed,scroll-other-windowdisplays it in some window.When the selected window is the minibuffer, the next window is normally the leftmost one immediately above it. You can specify a different window to scroll, when the minibuffer is selected, by setting the variable
minibuffer-scroll-window. This variable has no effect when any other window is selected. When it is non-niland the minibuffer is selected, it takes precedence overother-window-scroll-buffer. See Definition of minibuffer-scroll-window.When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case,
scroll-other-windowattempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message `End of buffer'.
If this variable is non-
nil, it tellsscroll-other-windowwhich buffer's window to scroll.
This option specifies the size of the scroll margin—a minimum number of lines between point and the top or bottom of a window. Whenever point gets within this many lines of the top or bottom of the window, redisplay scrolls the text automatically (if possible) to move point out of the margin, closer to the center of the window.
This variable controls how scrolling is done automatically when point moves off the screen (or into the scroll margin). If the value is a positive integer n, then redisplay scrolls the text up to n lines in either direction, if that will bring point back into proper view. This behavior is called conservative scrolling. Otherwise, scrolling happens in the usual way, under the control of other variables such as
scroll-up-aggressivelyandscroll-down-aggressively.The default value is zero, which means that conservative scrolling never happens.
The value of this variable should be either
nilor a fraction f between 0 and 1. If it is a fraction, that specifies where on the screen to put point when scrolling down. More precisely, when a window scrolls down because point is above the window start, the new start position is chosen to put point f part of the window height from the top. The larger f, the more aggressive the scrolling.A value of
nilis equivalent to .5, since its effect is to center point. This variable automatically becomes buffer-local when set in any fashion.
Likewise, for scrolling up. The value, f, specifies how far point should be placed from the bottom of the window; thus, as with
scroll-up-aggressively, a larger value scrolls more aggressively.
This variable is an older variant of
scroll-conservatively. The difference is that if its value is n, that permits scrolling only by precisely n lines, not a smaller number. This feature does not work withscroll-margin. The default value is zero.
If this option is
t, whenever a scrolling command moves point off-window, Emacs tries to adjust point to keep the cursor at its old vertical position in the window, rather than the window edge.If the value is non-
niland nott, Emacs adjusts point to keep the cursor at the same vertical position, even if the scrolling command didn't move point off-window.This option affects all scroll commands that have a non-
nilscroll-commandsymbol property.
The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example,
scroll-upwith an argument ofnilscrolls so that this many lines at the bottom of the window appear instead at the top. The default value is2.
If this option is
nil(the default),scroll-up-commandandscroll-down-commandsimply signal an error when no more scrolling is possible.If the value is
t, these commands instead move point to the beginning or end of the buffer (depending on scrolling direction); only if point is already on that position do they signal an error.
This function scrolls the text in the selected window so that point is displayed at a specified vertical position within the window. It does not move point with respect to the text.
If count is a non-negative number, that puts the line containing point count lines down from the top of the window. If count is a negative number, then it counts upward from the bottom of the window, so that −1 stands for the last usable line in the window.
If count is
nil(or a non-nillist),recenterputs the line containing point in the middle of the window. If count isnil, this function may redraw the frame, according to the value ofrecenter-redisplay.When
recenteris called interactively, count is the raw prefix argument. Thus, typing C-u as the prefix sets the count to a non-nillist, while typing C-u 4 sets count to 4, which positions the current line four lines from the top.With an argument of zero,
recenterpositions the current line at the top of the window. The commandrecenter-top-bottomoffers a more convenient way to achieve this.
This function is like
recenter, except that when the selected window is part of a group of windows (see Window Group),recenter-window-groupscrolls the entire group. This condition holds when the buffer local variablerecenter-window-group-functionis set to a function. In this case,recenter-window-groupcalls the function with the argument count, then returns its result. The argument count has the same meaning as inrecenter, but with respect to the entire window group.
If this variable is non-
nil, callingrecenterwith anilargument redraws the frame. The default value istty, which means only redraw the frame if it is a tty frame.
This command, which is the default binding for C-l, acts like
recenter, except if called with no argument. In that case, successive calls place point according to the cycling order defined by the variablerecenter-positions.
This variable controls how
recenter-top-bottombehaves when called with no argument. The default value is(middle top bottom), which means that successive calls ofrecenter-top-bottomwith no argument cycle between placing point at the middle, top, and bottom of the window.
Vertical fractional scrolling means shifting text in a window up or down by a specified multiple or fraction of a line. Each window has a vertical scroll position, which is a number, never less than zero. It specifies how far to raise the contents of the window. Raising the window contents generally makes all or part of some lines disappear off the top, and all or part of some other lines appear at the bottom. The usual value is zero.
The vertical scroll position is measured in units of the normal line height, which is the height of the default font. Thus, if the value is .5, that means the window contents are scrolled up half the normal line height. If it is 3.3, that means the window contents are scrolled up somewhat over three times the normal line height.
What fraction of a line the vertical scrolling covers, or how many lines, depends on what the lines contain. A value of .5 could scroll a line whose height is very short off the screen, while a value of 3.3 could scroll just part of the way through a tall line or an image.
This function returns the current vertical scroll position of window. The default for window is the selected window. If pixels-p is non-
nil, the return value is measured in pixels, rather than in units of the normal line height.(window-vscroll) => 0
This function sets window's vertical scroll position to lines. If window is
nil, the selected window is used. The argument lines should be zero or positive; if not, it is taken as zero.The actual vertical scroll position must always correspond to an integral number of pixels, so the value you specify is rounded accordingly.
The return value is the result of this rounding.
(set-window-vscroll (selected-window) 1.2) => 1.13If pixels-p is non-
nil, lines specifies a number of pixels. In this case, the return value is lines.
If this variable is non-
nil, theline-move,scroll-up, andscroll-downfunctions will automatically modify the vertical scroll position to scroll through display rows that are taller than the height of the window, for example in the presence of large images.
Horizontal scrolling means shifting the image in the window left or right by a specified multiple of the normal character width. Each window has a horizontal scroll position, which is a number, never less than zero. It specifies how far to shift the contents left. Shifting the window contents left generally makes all or part of some characters disappear off the left, and all or part of some other characters appear at the right. The usual value is zero.
The horizontal scroll position is measured in units of the normal character width, which is the width of space in the default font. Thus, if the value is 5, that means the window contents are scrolled left by 5 times the normal character width. How many characters actually disappear off to the left depends on their width, and could vary from line to line.
Because we read from side to side in the inner loop, and from top to bottom in the outer loop, the effect of horizontal scrolling is not like that of textual or vertical scrolling. Textual scrolling involves selection of a portion of text to display, and vertical scrolling moves the window contents contiguously; but horizontal scrolling causes part of each line to go off screen.
Usually, no horizontal scrolling is in effect; then the leftmost column is at the left edge of the window. In this state, scrolling to the right is meaningless, since there is no data to the left of the edge to be revealed by it; so this is not allowed. Scrolling to the left is allowed; it scrolls the first columns of text off the edge of the window and can reveal additional columns on the right that were truncated before. Once a window has a nonzero amount of leftward horizontal scrolling, you can scroll it back to the right, but only so far as to reduce the net horizontal scroll to zero. There is no limit to how far left you can scroll, but eventually all the text will disappear off the left edge.
If auto-hscroll-mode is set, redisplay automatically alters
the horizontal scrolling of a window as necessary to ensure that point
is always visible. However, you can still set the horizontal
scrolling value explicitly. The value you specify serves as a lower
bound for automatic scrolling, i.e., automatic scrolling will not
scroll a window to a column less than the specified one.
This function scrolls the selected window count columns to the left (or to the right if count is negative). The default for count is the window width, minus 2.
The return value is the total amount of leftward horizontal scrolling in effect after the change—just like the value returned by
window-hscroll(below).Note that text in paragraphs whose base direction is right-to-left (see Bidirectional Display) moves in the opposite direction: e.g., it moves to the right when
scroll-leftis invoked with a positive value of count.Once you scroll a window as far right as it can go, back to its normal position where the total leftward scrolling is zero, attempts to scroll any farther right have no effect.
If set-minimum is non-
nil, the new scroll amount becomes the lower bound for automatic scrolling; that is, automatic scrolling will not scroll a window to a column less than the value returned by this function. Interactive calls pass non-nilfor set-minimum.
This function scrolls the selected window count columns to the right (or to the left if count is negative). The default for count is the window width, minus 2. Aside from the direction of scrolling, this works just like
scroll-left.
This function returns the total leftward horizontal scrolling of window—the number of columns by which the text in window is scrolled left past the left margin. (In right-to-left paragraphs, the value is the total amount of the rightward scrolling instead.) The default for window is the selected window.
The return value is never negative. It is zero when no horizontal scrolling has been done in window (which is usually the case).
(window-hscroll) => 0 (scroll-left 5) => 5 (window-hscroll) => 5
This function sets horizontal scrolling of window. The value of columns specifies the amount of scrolling, in terms of columns from the left margin (right margin in right-to-left paragraphs). The argument columns should be zero or positive; if not, it is taken as zero. Fractional values of columns are not supported at present.
Note that
set-window-hscrollmay appear not to work if you test it by evaluating a call with M-: in a simple way. What happens is that the function sets the horizontal scroll value and returns, but then redisplay adjusts the horizontal scrolling to make point visible, and this overrides what the function did. You can observe the function's effect if you call it while point is sufficiently far from the left margin that it will remain visible.The value returned is columns.
(set-window-hscroll (selected-window) 10) => 10
Here is how you can determine whether a given position position is off the screen due to horizontal scrolling:
(defun hscroll-on-screen (window position)
(save-excursion
(goto-char position)
(and
(>= (- (current-column) (window-hscroll window)) 0)
(< (- (current-column) (window-hscroll window))
(window-width window)))))
This section describes functions that report the position of a window. Most of these functions report positions relative to an origin at the native position of the window's frame (see Frame Geometry). Some functions report positions relative to the origin of the display of the window's frame. In any case, the origin has the coordinates (0, 0) and X and Y coordinates increase rightward and downward respectively.
For the following functions, X and Y coordinates are reported in integer character units, i.e., numbers of lines and columns respectively. On a graphical display, each “line” and “column” corresponds to the height and width of the default character specified by the frame's default font (see Frame Font).
This function returns a list of the edge coordinates of window. If window is omitted or
nil, it defaults to the selected window.The return value has the form
(left top right bottom). These list elements are, respectively, the X coordinate of the leftmost column occupied by the window, the Y coordinate of the topmost row, the X coordinate one column to the right of the rightmost column, and the Y coordinate one row down from the bottommost row.Note that these are the actual outer edges of the window, including any header line, mode line, scroll bar, fringes, window divider and display margins. On a text terminal, if the window has a neighbor on its right, its right edge includes the separator line between the window and its neighbor.
If the optional argument body is
nil, this means to return the edges corresponding to the total size of window. body non-nilmeans to return the edges of window's body (aka text area). If body is non-nil, window must specify a live window.If the optional argument absolute is
nil, this means to return edges relative to the native position of window's frame. absolute non-nilmeans to return coordinates relative to the origin (0, 0) of window's display. On non-graphical systems this argument has no effect.If the optional argument pixelwise is
nil, this means to return the coordinates in terms of the default character width and height of window's frame (see Frame Font), rounded if necessary. pixelwise non-nilmeans to return the coordinates in pixels. Note that the pixel specified by right and bottom is immediately outside of these edges. If absolute is non-nil, pixelwise is implicitly non-niltoo.
This function returns the edges of window's body (see Window Sizes). Calling
(window-body-edges window)is equivalent to calling(window-edges window t), see above.
The following functions can be used to relate a set of frame-relative coordinates to a window:
This function returns the live window at the coordinates x and y given in default character sizes (see Frame Font) relative to the native position of frame (see Frame Geometry).
If there is no window at that position, the return value is
nil. If frame is omitted ornil, it defaults to the selected frame.
This function checks whether a window window occupies the frame relative coordinates coordinates, and if so, which part of the window that is. window should be a live window.
coordinates should be a cons cell of the form
(x.y), where x and y are given in default character sizes (see Frame Font) relative to the native position of window's frame (see Frame Geometry).If there is no window at the specified position, the return value is
nil. Otherwise, the return value is one of the following:
(relx.rely)- The coordinates are inside window. The numbers relx and rely are the equivalent window-relative coordinates for the specified position, counting from 0 at the top left corner of the window.
mode-line- The coordinates are in the mode line of window.
header-line- The coordinates are in the header line of window.
right-divider- The coordinates are in the divider separating window from a window on the right.
bottom-divider- The coordinates are in the divider separating window from a window beneath.
vertical-line- The coordinates are in the vertical line between window and its neighbor to the right. This value occurs only if the window doesn't have a scroll bar; positions in a scroll bar are considered outside the window for these purposes.
left-fringeright-fringe- The coordinates are in the left or right fringe of the window.
left-marginright-margin- The coordinates are in the left or right margin of the window.
nil- The coordinates are not in any part of window.
The function
coordinates-in-window-pdoes not require a frame as argument because it always uses the frame that window is on.
The following functions return window positions in pixels, rather than character units. Though mostly useful on graphical displays, they can also be called on text terminals, where the screen area of each text character is taken to be one pixel.
This function returns a list of pixel coordinates for the edges of window. Calling
(window-pixel-edges window)is equivalent to calling(window-edges window nil nil t), see above.
This function returns the pixel edges of window's body. Calling
(window-body-pixel-edges window)is equivalent to calling(window-edges window t nil t), see above.
The following functions return window positions in pixels, relative to the origin of the display screen rather than that of the frame:
This function returns the pixel coordinates of WINDOW relative to an origin at (0, 0) of the display of window's frame. Calling
(window-absolute-pixel-edges)is equivalent to calling(window-edges window nil t t), see above.
This function returns the pixel coordinates of WINDOW's body relative to an origin at (0, 0) of the display of window's frame. Calling
(window-absolute-body-pixel-edges window)is equivalent to calling(window-edges window t t t), see above.Combined with
set-mouse-absolute-pixel-position, this function can be used to move the mouse pointer to an arbitrary buffer position visible in some window:(let ((edges (window-absolute-body-pixel-edges)) (position (pos-visible-in-window-p nil nil t))) (set-mouse-absolute-pixel-position (+ (nth 0 edges) (nth 0 position)) (+ (nth 1 edges) (nth 1 position))))On a graphical terminal this form “warps” the mouse cursor to the upper left corner of the glyph at the selected window's point. A position calculated this way can be also used to show a tooltip window there.
The following function returns the screen coordinates of a buffer position visible in a window:
If the buffer position position is visible in window window, this function returns the display coordinates of the upper/left corner of the glyph at position. The return value is a cons of the X- and Y-coordinates of that corner, relative to an origin at (0, 0) of window's display. It returns
nilif position is not visible in window.window must be a live window and defaults to the selected window. position defaults to the value of
window-pointof window.This means that in order to move the mouse pointer to the position of point in the selected window, it's sufficient to write:
(let ((position (window-absolute-pixel-position))) (set-mouse-absolute-pixel-position (car position) (cdr position)))
A window configuration records the entire layout of one
frame—all windows, their sizes, which buffers they contain, how those
buffers are scrolled, and their value of point; also their
fringes, margins, and scroll bar settings. It also includes the value
of minibuffer-scroll-window. As a special exception, the window
configuration does not record the value of point in the selected window
for the current buffer.
You can bring back an entire frame layout by restoring a previously saved window configuration. If you want to record the layout of all frames instead of just one, use a frame configuration instead of a window configuration. See Frame Configurations.
This function returns a new object representing frame's current window configuration. The default for frame is the selected frame. The variable
window-persistent-parametersspecifies which window parameters (if any) are saved by this function. See Window Parameters.
This function restores the configuration of windows and buffers as specified by configuration, for the frame that configuration was created for.
The argument configuration must be a value that was previously returned by
current-window-configuration. The configuration is restored in the frame from which configuration was made, whether that frame is selected or not. This always counts as a window size change and triggers execution of thewindow-size-change-functions(see Window Hooks), becauseset-window-configurationdoesn't know how to tell whether the new configuration actually differs from the old one.If the frame from which configuration was saved is dead, all this function does is restore the three variables
window-min-height,window-min-widthandminibuffer-scroll-window. In this case, the function returnsnil. Otherwise, it returnst.Here is a way of using this function to get the same effect as
save-window-excursion:(let ((config (current-window-configuration))) (unwind-protect (progn (split-window-below nil) ...) (set-window-configuration config)))
This macro records the window configuration of the selected frame, executes forms in sequence, then restores the earlier window configuration. The return value is the value of the final form in forms.
Most Lisp code should not use this macro;
save-selected-windowis typically sufficient. In particular, this macro cannot reliably prevent the code in forms from opening new windows, because new windows might be opened in other frames (see Choosing Window), andsave-window-excursiononly saves and restores the window configuration on the current frame.Do not use this macro in
window-size-change-functions; exiting the macro triggers execution ofwindow-size-change-functions, leading to an endless loop.
This function returns
tif object is a window configuration.
This function compares two window configurations as regards the structure of windows, but ignores the values of point and the saved scrolling positions—it can return
teven if those aspects differ.The function
equalcan also compare two window configurations; it regards configurations as unequal if they differ in any respect, even a saved point.
This function returns the frame for which the window configuration config was made.
Other primitives to look inside of window configurations would make sense, but are not implemented because we did not need them. See the file winner.el for some more operations on windows configurations.
The objects returned by current-window-configuration die
together with the Emacs process. In order to store a window
configuration on disk and read it back in another Emacs session, you
can use the functions described next. These functions are also useful
to clone the state of a frame into an arbitrary live window
(set-window-configuration effectively clones the windows of a
frame into the root window of that very frame only).
This function returns the state of window as a Lisp object. The argument window must be a valid window and defaults to the root window of the selected frame.
If the optional argument writable is non-
nil, this means to not use markers for sampling positions likewindow-pointorwindow-start. This argument should be non-nilwhen the state will be written to disk and read back in another session.Together, the argument writable and the variable
window-persistent-parametersspecify which window parameters are saved by this function. See Window Parameters.
The value returned by window-state-get can be used in the same
session to make a clone of a window in another window. It can be also
written to disk and read back in another session. In either case, use
the following function to restore the state of the window.
This function puts the window state state into window. The argument state should be the state of a window returned by an earlier invocation of
window-state-get, see above. The optional argument window can be either a live window or an internal window (see Windows and Frames) and defaults to the selected one. If window is not live, it is replaced by a live window before putting state into it.If the optional argument ignore is non-
nil, it means to ignore minimum window sizes and fixed-size restrictions. If ignore issafe, this means windows can get as small as one line and/or two columns.
This section describes how window parameters can be used to associate additional information with windows.
This function returns window's value for parameter. The default for window is the selected window. If window has no setting for parameter, this function returns
nil.
This function returns all parameters of window and their values. The default for window is the selected window. The return value is either
nil, or an association list whose elements have the form(parameter.value).
This function sets window's value of parameter to value and returns value. The default for window is the selected window.
By default, the functions that save and restore window configurations or the
states of windows (see Window Configurations) do not care about
window parameters. This means that when you change the value of a
parameter within the body of a save-window-excursion, the
previous value is not restored when that macro exits. It also means
that when you restore via window-state-put a window state saved
earlier by window-state-get, all cloned windows have their
parameters reset to nil. The following variable allows you to
override the standard behavior:
This variable is an alist specifying which parameters get saved by
current-window-configurationandwindow-state-get, and subsequently restored byset-window-configurationandwindow-state-put. See Window Configurations.The car of each entry of this alist is a symbol specifying the parameter. The cdr should be one of the following:
nil- This value means the parameter is saved neither by
window-state-getnor bycurrent-window-configuration.
t- This value specifies that the parameter is saved by
current-window-configurationand (provided its writable argument isnil) bywindow-state-get.
writable- This means that the parameter is saved unconditionally by both
current-window-configurationandwindow-state-get. This value should not be used for parameters whose values do not have a read syntax. Otherwise, invokingwindow-state-putin another session may fail with aninvalid-read-syntaxerror.
Some functions (notably delete-window,
delete-other-windows and split-window), may behave specially
when their window argument has a parameter set. You can override
such special behavior by binding the following variable to a
non-nil value:
If this variable is non-
nil, some standard functions do not process window parameters. The functions currently affected by this aresplit-window,delete-window,delete-other-windows, andother-window.An application can bind this variable to a non-
nilvalue around calls to these functions. If it does so, the application is fully responsible for correctly assigning the parameters of all involved windows when exiting that function.
The following parameters are currently used by the window management code:
delete-windowdelete-window
(see Deleting Windows).
delete-other-windowsdelete-other-windows
(see Deleting Windows).
split-windowsplit-window
(see Splitting Windows).
other-windowother-window
(see Cyclic Window Ordering).
no-other-windowother-window
(see Cyclic Window Ordering).
clone-ofwindow-state-get (see Window Configurations).
preserved-sizenil means
vertical and t horizontal, and a size in pixels. If this window
displays the specified buffer and its size in the indicated direction
equals the size specified by this parameter, then Emacs will try to
preserve the size of this window in the indicated direction. This
parameter is installed and updated by the function
window-preserve-size (see Preserving Window Sizes).
quit-restorequit-restore-window
(see Quitting Windows). It contains four elements:
The first element is one of the symbols window, meaning that the
window has been specially created by display-buffer; frame,
a separate frame has been created; same, the window has
displayed the same buffer before; or other, the window showed
another buffer before.
The second element is either one of the symbols window or
frame, or a list whose elements are the buffer shown in the
window before, that buffer's window start and window point positions,
and the window's height at that time.
The third element is the window selected at the time the parameter was
created. The function quit-restore-window tries to reselect that
window when it deletes the window passed to it as argument.
The fourth element is the buffer whose display caused the creation of
this parameter. quit-restore-window deletes the specified window
only if it still shows that buffer.
There are additional parameters window-atom and window-side;
these are reserved and should not be used by applications.
This section describes how a Lisp program can take action whenever a
window displays a different part of its buffer or a different buffer.
There are three actions that can change this: scrolling the window,
switching buffers in the window, and changing the size of the window.
The first two actions run window-scroll-functions; the last runs
window-size-change-functions.
This variable holds a list of functions that Emacs should call before redisplaying a window with scrolling. Displaying a different buffer in the window also runs these functions.
This variable is not a normal hook, because each function is called with two arguments: the window, and its new display-start position.
These functions must take care when using
window-end(see Window Start and End); if you need an up-to-date value, you must use the update argument to ensure you get it.Warning: don't use this feature to alter the way the window is scrolled. It's not designed for that, and such use probably won't work.
This variable holds a list of functions to be called if the size of any window changes for any reason. The functions are called at the beginning of a redisplay cycle, and just once for each frame on which size changes have occurred.
Each function receives the frame as its sole argument. There is no direct way to find out which windows on that frame have changed size, or precisely how. However, if a size-change function records, at each call, the existing windows and their sizes, it can also compare the present sizes and the previous sizes.
Creating or deleting windows counts as a size change, and therefore causes these functions to be called. Changing the frame size also counts, because it changes the sizes of the existing windows.
You may use
save-selected-windowin these functions (see Selecting Windows). However, do not usesave-window-excursion(see Window Configurations); exiting that macro counts as a size change, which would cause these functions to be called over and over.
A normal hook that is run every time you change the window configuration of an existing frame. This includes splitting or deleting windows, changing the sizes of windows, or displaying a different buffer in a window.
The buffer-local part of this hook is run once for each window on the affected frame, with the relevant window selected and its buffer current. The global part is run once for the modified frame, with that frame selected.
In addition, you can use jit-lock-register to register a Font
Lock fontification function, which will be called whenever parts of a
buffer are (re)fontified because a window was scrolled or its size
changed. See Other Font Lock Variables.
A frame is a screen object that contains one or more Emacs windows (see Windows). It is the kind of object called a “window” in the terminology of graphical environments; but we can't call it a “window” here, because Emacs uses that word in a different way. In Emacs Lisp, a frame object is a Lisp object that represents a frame on the screen. See Frame Type.
A frame initially contains a single main window and/or a minibuffer window; you can subdivide the main window vertically or horizontally into smaller windows. See Splitting Windows.
A terminal is a display device capable of displaying one or more Emacs frames. In Emacs Lisp, a terminal object is a Lisp object that represents a terminal. See Terminal Type.
There are two classes of terminals: text terminals and graphical terminals. Text terminals are non-graphics-capable displays, including xterm and other terminal emulators. On a text terminal, each Emacs frame occupies the terminal's entire screen; although you can create additional frames and switch between them, the terminal only shows one frame at a time. Graphical terminals, on the other hand, are managed by graphical display systems such as the X Window System, which allow Emacs to show multiple frames simultaneously on the same display.
On GNU and Unix systems, you can create additional frames on any available terminal, within a single Emacs session, regardless of whether Emacs was started on a text or graphical terminal. Emacs can display on both graphical and text terminals simultaneously. This comes in handy, for instance, when you connect to the same session from several remote locations. See Multiple Terminals.
This predicate returns a non-
nilvalue if object is a frame, andnilotherwise. For a frame, the value indicates which kind of display the frame uses:
t- The frame is displayed on a text terminal.
x- The frame is displayed on an X graphical terminal.
w32- The frame is displayed on a MS-Windows graphical terminal.
ns- The frame is displayed on a GNUstep or Macintosh Cocoa graphical terminal.
pc- The frame is displayed on an MS-DOS terminal.
This function returns the terminal object that displays frame. If frame is
nilor unspecified, it defaults to the selected frame.
This predicate returns a non-
nilvalue if object is a terminal that is live (i.e., not deleted), andnilotherwise. For live terminals, the return value indicates what kind of frames are displayed on that terminal; the list of possible values is the same as forframepabove.
To create a new frame, call the function make-frame.
This function creates and returns a new frame, displaying the current buffer.
The alist argument is an alist that specifies frame parameters for the new frame. See Frame Parameters. If you specify the
terminalparameter in alist, the new frame is created on that terminal. Otherwise, if you specify thewindow-systemframe parameter in alist, that determines whether the frame should be displayed on a text terminal or a graphical terminal. See Window Systems. If neither is specified, the new frame is created in the same terminal as the selected frame.Any parameters not mentioned in alist default to the values in the alist
default-frame-alist(see Initial Parameters); parameters not specified there default from the X resources or its equivalent on your operating system (see X Resources). After the frame is created, Emacs applies any parameters listed inframe-inherited-parameters(see below) and not present in the argument, taking the values from the frame that was selected whenmake-framewas called.Note that on multi-monitor displays (see Multiple Terminals), the window manager might position the frame differently than specified by the positional parameters in alist (see Position Parameters). For example, some window managers have a policy of displaying the frame on the monitor that contains the largest part of the window (a.k.a. the dominating monitor).
This function itself does not make the new frame the selected frame. See Input Focus. The previously selected frame remains selected. On graphical terminals, however, the windowing system may select the new frame for its own reasons.
An abnormal hook run by
make-frameafter it creates the frame. Each function inafter-make-frame-functionsreceives one argument, the frame just created.
This variable specifies the list of frame parameters that a newly created frame inherits from the currently selected frame. For each parameter (a symbol) that is an element in the list and is not present in the argument to
make-frame, the function sets the value of that parameter in the created frame to its value in the selected frame.
Emacs represents each terminal as a terminal object data type (see Terminal Type). On GNU and Unix systems, Emacs can use multiple terminals simultaneously in each session. On other systems, it can only use a single terminal. Each terminal object has the following attributes:
terminal-live-p (i.e., x,
t, w32, ns, or pc). See Frames.
There is no primitive for creating terminal objects. Emacs creates
them as needed, such as when you call make-frame-on-display
(described below).
This function returns the file name of the device used by terminal. If terminal is omitted or
nil, it defaults to the selected frame's terminal. terminal can also be a frame, meaning that frame's terminal.
This function returns a terminal whose device name is given by device. If device is a string, it can be either the file name of a terminal device, or the name of an X display of the form `host:server.screen'. If device is a frame, this function returns that frame's terminal;
nilmeans the selected frame. Finally, if device is a terminal object that represents a live terminal, that terminal is returned. The function signals an error if its argument is none of the above.
This function deletes all frames on terminal and frees the resources used by it. It runs the abnormal hook
delete-terminal-functions, passing terminal as the argument to each function.If terminal is omitted or
nil, it defaults to the selected frame's terminal. terminal can also be a frame, meaning that frame's terminal.Normally, this function signals an error if you attempt to delete the sole active terminal, but if force is non-
nil, you are allowed to do so. Emacs automatically calls this function when the last frame on a terminal is deleted (see Deleting Frames).
An abnormal hook run by
delete-terminal. Each function receives one argument, the terminal argument passed todelete-terminal. Due to technical details, the functions may be called either just before the terminal is deleted, or just afterwards.
A few Lisp variables are terminal-local; that is, they have a
separate binding for each terminal. The binding in effect at any time
is the one for the terminal that the currently selected frame belongs
to. These variables include default-minibuffer-frame,
defining-kbd-macro, last-kbd-macro, and
system-key-alist. They are always terminal-local, and can
never be buffer-local (see Buffer-Local Variables).
On GNU and Unix systems, each X display is a separate graphical
terminal. When Emacs is started from within the X window system, it
uses the X display specified by the DISPLAY environment
variable, or by the `--display' option (see Initial Options). Emacs can connect to other X displays
via the command make-frame-on-display. Each X display has its
own selected frame and its own minibuffer windows; however, only one
of those frames is the selected frame at any given moment
(see Input Focus). Emacs can even connect to other text
terminals, by interacting with the emacsclient program.
See Emacs Server.
A single X server can handle more than one display. Each X display has a three-part name, `hostname:displaynumber.screennumber'. The first part, hostname, specifies the name of the machine to which the display is physically connected. The second part, displaynumber, is a zero-based number that identifies one or more monitors connected to that machine that share a common keyboard and pointing device (mouse, tablet, etc.). The third part, screennumber, identifies a zero-based screen number (a separate monitor) that is part of a single monitor collection on that X server. When you use two or more screens belonging to one server, Emacs knows by the similarity in their names that they share a single keyboard.
Systems that don't use the X window system, such as MS-Windows, don't support the notion of X displays, and have only one display on each host. The display name on these systems doesn't follow the above 3-part format; for example, the display name on MS-Windows systems is a constant string `w32', and exists for compatibility, so that you could pass it to functions that expect a display name.
This function creates and returns a new frame on display, taking the other frame parameters from the alist parameters. display should be the name of an X display (a string).
Before creating the frame, this function ensures that Emacs is set up to display graphics. For instance, if Emacs has not processed X resources (e.g., if it was started on a text terminal), it does so at this time. In all other respects, this function behaves like
make-frame(see Creating Frames).
This function returns a list that indicates which X displays Emacs has a connection to. The elements of the list are strings, and each one is a display name.
This function opens a connection to the X display display, without creating a frame on that display. Normally, Emacs Lisp programs need not call this function, as
make-frame-on-displaycalls it automatically. The only reason for calling it is to check whether communication can be established with a given X display.The optional argument xrm-string, if not
nil, is a string of resource names and values, in the same format used in the .Xresources file. See X Resources. These values apply to all Emacs frames created on this display, overriding the resource values recorded in the X server. Here's an example of what this string might look like:"*BorderWidth: 3\n*InternalBorder: 2\n"If must-succeed is non-
nil, failure to open the connection terminates Emacs. Otherwise, it is an ordinary Lisp error.
This function closes the connection to display display. Before you can do this, you must first delete all the frames that were open on that display (see Deleting Frames).
On some multi-monitor setups, a single X display outputs to more
than one physical monitor. You can use the functions
display-monitor-attributes-list and frame-monitor-attributes
to obtain information about such setups.
This function returns a list of physical monitor attributes on display, which can be a display name (a string), a terminal, or a frame; if omitted or
nil, it defaults to the selected frame's display. Each element of the list is an association list, representing the attributes of a physical monitor. The first element corresponds to the primary monitor. The attribute keys and values are:
- `geometry'
- Position of the top-left corner of the monitor's screen and its size, in pixels, as `(x y width height)'. Note that, if the monitor is not the primary monitor, some of the coordinates might be negative.
- `workarea'
- Position of the top-left corner and size of the work area (usable space) in pixels as `(x y width height)'. This may be different from `geometry' in that space occupied by various window manager features (docks, taskbars, etc.) may be excluded from the work area. Whether or not such features actually subtract from the work area depends on the platform and environment. Again, if the monitor is not the primary monitor, some of the coordinates might be negative.
- `mm-size'
- Width and height in millimeters as `(width height)'
- `frames'
- List of frames that this physical monitor dominates (see below).
- `name'
- Name of the physical monitor as string.
- `source'
- Source of the multi-monitor information as string; e.g., `XRandr' or `Xinerama'.
x, y, width, and height are integers. `name' and `source' may be absent.
A frame is dominated by a physical monitor when either the largest area of the frame resides in that monitor, or (if the frame does not intersect any physical monitors) that monitor is the closest to the frame. Every (non-tooltip) frame (whether visible or not) in a graphical display is dominated by exactly one physical monitor at a time, though the frame can span multiple (or no) physical monitors.
Here's an example of the data produced by this function on a 2-monitor display:
(display-monitor-attributes-list) => (((geometry 0 0 1920 1080) ;; Left-hand, primary monitor (workarea 0 0 1920 1050) ;; A taskbar occupies some of the height (mm-size 677 381) (name . "DISPLAY1") (frames #<frame emacs@host *Messages* 0x11578c0> #<frame emacs@host *scratch* 0x114b838>)) ((geometry 1920 0 1680 1050) ;; Right-hand monitor (workarea 1920 0 1680 1050) ;; Whole screen can be used (mm-size 593 370) (name . "DISPLAY2") (frames)))
This function returns the attributes of the physical monitor dominating (see above) frame, which defaults to the selected frame.
The geometry of a frame depends on the toolkit that was used to build
this instance of Emacs and the terminal that displays the frame. This
chapter describes these dependencies and some of the functions to deal
with them. Note that the frame argument of all of these functions
has to specify a live frame (see Deleting Frames). If omitted or
nil, it specifies the selected frame (see Input Focus).
The drawing below sketches the layout of a frame on a graphical terminal:
<------------ Outer Frame Width ----------->
___________________________________________
^(0) ___________ External Border __________ |
| | |_____________ Title Bar ______________| |
| | (1)_____________ Menu Bar ______________| | ^
| | (2)_____________ Tool Bar ______________| | ^
| | (3) _________ Internal Border ________ | | ^
| | | | ^ | | | |
| | | | | | | | |
Outer | | | Inner | | | Native
Frame | | | Frame | | | Frame
Height | | | Height | | | Height
| | | | | | | | |
| | | |<--+--- Inner Frame Width ------->| | | |
| | | | | | | | |
| | | |___v______________________________| | | |
| | |___________ Internal Border __________| | v
v |______________ External Border _____________|
<-------- Native Frame Width -------->
In practice not all of the areas shown in the drawing will or may be present. The meaning of these areas is:
The upper left corner of the outer frame (indicated by `(0)' in the
drawing above) is the outer position or the frame. It is
specified by and settable via the left and top frame
parameters (see Position Parameters) as well as the functions
frame-position and set-frame-position (see Size and Position).
The external border should not be confused with the outer
border specified by the border-width frame parameter
(see Layout Parameters). Since the outer border is usually ignored
on most platforms it is not covered here.
The top left corner of the native frame specifies the native position of the frame. (1)–(3) in the drawing above indicate that position for the various builds:
Accordingly, the native height of a frame includes the height of the tool bar but not that of the menu bar (Lucid, Motif, Windows) or those of the menu bar and the tool bar (non-toolkit and text terminal frames).
The native position of a frame is the reference position of functions
that set or return the current position of the mouse (see Mouse Position) and for functions dealing with the position of windows like
window-edges, window-at or coordinates-in-window-p
(see Coordinates and Windows).
As a rule, the inner frame is subdivided into the frame's root window
(see Windows and Frames) and the frame's minibuffer window
(see Minibuffer Windows). There are two notable exceptions to this
rule: A minibuffer-less frame contains a root window only and does
not contain a minibuffer window. A minibuffer-only frame contains
only a minibuffer window which also serves as that frame's root window.
See Initial Parameters for how to create such frame
configurations.
The absolute position of a frame or its edges is usually given in terms of pixels counted from an origin at position (0, 0) of the frame's display. Note that with multiple monitors the origin does not necessarily coincide with the top left corner of the entire usable display area. Hence the absolute outer position of a frame or the absolute positions of the edges of the outer, native or inner frame can be negative in such an environment even when that frame is completely visible.
For a frame on a graphical terminal the following function returns the sizes of the areas described above:
This function returns geometric attributes of frame. The return value is an association list of the attributes listed below. All coordinate, height and width values are integers counting pixels.
outer-position- A cons of the absolute X- and Y-coordinates of the outer position of frame, relative to the origin at position (0, 0) of frame's display.
outer-size- A cons of the outer width and height of frame.
external-border-size- A cons of the horizontal and vertical width of frame's external borders as supplied by the window manager. If the window manager doesn't supply these values, Emacs will try to guess them from the coordinates of the outer and inner frame.
title-bar-size- A cons of the width and height of the title bar of frame as supplied by the window manager or operating system. If both of them are zero, the frame has no title bar. If only the width is zero, Emacs was not able to retrieve the width information.
menu-bar-external- If non-
nil, this means the menu bar is external (not part of the native frame of frame).
menu-bar-size- A cons of the width and height of the menu bar of frame.
tool-bar-external- If non-
nil, this means the tool bar is external (not part of the native frame of frame).
tool-bar-position- This tells on which side the tool bar on frame is and can be one of
left,top,rightorbottom. The only toolkit that currently supports a value other thantopis GTK+.
tool-bar-size- A cons of the width and height of the tool bar of frame.
internal-border-width- The width of the internal border of frame.
The following function can be used to retrieve the edges of the outer, native and inner frame.
This function returns the edges of the outer, native or inner frame of frame. frame must be a live frame and defaults to the selected one. The list returned has the form (left top right bottom) where all values are in pixels relative to the position (0, 0) of frame's display. For terminal frames left and top are both zero.
Optional argument type specifies the type of the edges to return: type
outer-edgesmeans to return the outer edges of frame,native-edges(ornil) means to return its native edges andinner-edgesmeans to return its inner edges.Notice that the pixels at the positions bottom and right lie immediately outside the corresponding frame. This means that if you have, for example, two side-by-side frames positioned such that the right outer edge of the frame on the left equals the left outer edge of the frame on the right, the pixels representing that edge are part of the frame on the right.
Each frame has a default font which specifies the default character size for that frame. This size is meant when retrieving or changing the size of a frame in terms of columns or lines (see Size Parameters). It is also used when resizing (see Window Sizes) or splitting (see Splitting Windows) windows.
The terms line height and canonical character height are sometimes used instead of “default character height”. Similarly, the terms column width and canonical character width are used instead of “default character width”.
These functions return the default height and width of a character in frame, measured in pixels. Together, these values establish the size of the default font on frame. The values depend on the choice of font for frame, see Font and Color Parameters.
The default font can be also set directly with the following function:
This sets the default font to font. When called interactively, it prompts for the name of a font, and uses that font on the selected frame. When called from Lisp, font should be a font name (a string), a font object, font entity, or a font spec.
If the optional argument keep-size is
nil, this keeps the number of frame lines and columns fixed. (If non-nil, the optionframe-inhibit-implied-resizedescribed in the next section will override this.) If keep-size is non-nil(or with a prefix argument), it tries to keep the size of the display area of the current frame fixed by adjusting the number of lines and columns.If the optional argument frames is
nil, this applies the font to the selected frame only. If frames is non-nil, it should be a list of frames to act upon, ortmeaning all existing and all future graphical frames.
You can read or change the position of a frame using the frame
parameters left and top (see Position Parameters) and
its size using the height and width parameters
(see Size Parameters). Here are some special features for working
with sizes and positions. For all of these functions the argument
frame must denote a live frame and defaults to the selected frame.
This function returns the outer position (see Frame Layout) of frame in pixels. The value is a cons giving the coordinates of the top left corner of the outer frame of frame relative to an origin at the position (0, 0) of the frame's display. On a text terminal frame both values are zero.
This function sets the outer frame position of frame to X and Y. The latter arguments specify pixels and normally count from an origin at the position (0, 0) of frame's display.
A negative parameter value positions the right edge of the outer frame by -x pixels left from the right edge of the screen or the bottom edge by -y pixels up from the bottom edge of the screen.
This function has no effect on text terminal frames.
These functions return the inner height and width (the height and width of the display area, see Frame Layout) of frame in pixels. For a text terminal, the results are in characters rather than pixels.
These functions return the height and width of the text area of frame (see Frame Layout), measured in pixels. For a text terminal, the results are in characters rather than pixels.
The value returned by
frame-text-heightdiffers from that returned byframe-pixel-heightby not including the heights of any internal tool bar or menu bar, the height of one horizontal scroll bar and the widths of the internal border.The value returned by
frame-text-widthdiffers from that returned byframe-pixel-widthby not including the width of one vertical scroll bar, the widths of one left and one right fringe and the widths of the internal border.
These functions return the height and width of the text area of frame, measured in units of the default font height and width of frame (see Frame Font). These functions are plain shorthands for writing
(frame-parameter frame 'height)and(frame-parameter frame 'width).If the text area of frame measured in pixels is not a multiple of its default font size, the values returned by these functions are rounded down to the number of characters of the default font that fully fit into the text area.
If this option is
nil, a frame's size is usually rounded to a multiple of the current values of that frame'sframe-char-heightandframe-char-widthwhenever the frame is resized. If this is non-nil, no rounding occurs, hence frame sizes can increase/decrease by one pixel.Setting this variable usually causes the next resize operation to pass the corresponding size hints to the window manager. This means that this variable should be set only in a user's initial file; applications should never bind it temporarily.
The precise meaning of a value of
nilfor this option depends on the toolkit used. Dragging the external border with the mouse is done character-wise provided the window manager is willing to process the corresponding size hints. Callingset-frame-size(see below) with arguments that do not specify the frame size as an integer multiple of its character size, however, may: be ignored, cause a rounding (GTK+), or be accepted (Lucid, Motif, MS-Windows).With some window managers you may have to set this to non-
nilin order to make a frame appear truly maximized or full-screen.
This function sets the size of the text area of frame, measured in terms of the canonical height and width of a character on frame (see Frame Font).
The optional argument pixelwise non-
nilmeans to measure the new width and height in units of pixels instead. Note that ifframe-resize-pixelwiseisnil, some toolkits may refuse to fully honor the request if it does not increase/decrease the frame size to a multiple of its character size.
This function resizes the text area of frame to a height of height lines. The sizes of existing windows in frame are altered proportionally to fit.
If pretend is non-
nil, then Emacs displays height lines of output in frame, but does not change its value for the actual height of the frame. This is only useful on text terminals. Using a smaller height than the terminal actually implements may be useful to reproduce behavior observed on a smaller screen, or if the terminal malfunctions when using its whole screen. Setting the frame height directly does not always work, because knowing the correct actual size may be necessary for correct cursor positioning on text terminals.The optional fourth argument pixelwise non-
nilmeans that frame should be height pixels high. Note that ifframe-resize-pixelwiseisnil, some toolkits may refuse to fully honor the request if it does not increase/decrease the frame height to a multiple of its character height.
This function sets the width of the text area of frame, measured in characters. The argument pretend has the same meaning as in
set-frame-height.The optional fourth argument pixelwise non-
nilmeans that frame should be width pixels wide. Note that ifframe-resize-pixelwiseisnil, some toolkits may refuse to fully honor the request if it does not increase/decrease the frame width to a multiple of its character width.
None of these three functions will make a frame smaller than needed to display all of its windows together with their scroll bars, fringes, margins, dividers, mode and header lines. This contrasts with requests by the window manager triggered, for example, by dragging the external border of a frame with the mouse. Such requests are always honored by clipping, if necessary, portions that cannot be displayed at the right, bottom corner of the frame.
By default, Emacs tries to keep the number of lines and columns of a frame's text area unaltered when, for example, adding or removing the menu bar, changing the default font or setting the width of the frame's scroll bars. This means, however, that in such case Emacs must ask the window manager to resize the outer frame in order to accommodate the size change. Note that wrapping a menu or tool bar usually does not resize the frame's outer size, hence this will alter the number of displayed lines.
Occasionally, such implied frame resizing may be unwanted, for example, when the frame is maximized or made full-screen (where it's turned off by default). In other cases you can disable implied resizing with the following option:
If this option is
nil, changing font, menu bar, tool bar, internal borders, fringes or scroll bars of a specific frame may implicitly resize the frame's display area in order to preserve the number of columns or lines the frame displays. If this option is non-nil, no implied resizing is done.The value of this option can be also be a list of frame parameters. In that case, implied resizing is inhibited when changing a parameter that appears in this list. The frame parameters currently handled by this option are:
font,font-backend,internal-border-width,menu-bar-linesandtool-bar-lines.Changing any of the
scroll-bar-width,scroll-bar-height,vertical-scroll-bars,horizontal-scroll-bars,left-fringeandright-fringeframe parameters is handled as if the frame contained just one live window. This means, for example, that removing vertical scroll bars on a frame containing several side by side windows will shrink the outer frame width by the width of one scroll bar provided this option isniland keep it unchanged if this option is eithertor a list containingvertical-scroll-bars.The default value is
'(tool-bar-lines)for Lucid, Motif and Windows (which means that adding/removing a tool bar there does not change the outer frame height),nilon all other window systems including GTK+ (which means that changing any of the parameters listed above may change the size of the outer frame), andtotherwise (which means the outer frame size never changes implicitly when there's no window system support).Note that when a frame is not large enough to accommodate a change of any of the parameters listed above, Emacs may try to enlarge the frame even if this option is non-
nil.
A frame has many parameters that control its appearance and behavior. Just what parameters a frame has depends on what display mechanism it uses.
Frame parameters exist mostly for the sake of graphical displays.
Most frame parameters have no effect when applied to a frame on a text
terminal; only the height, width, name,
title, menu-bar-lines, buffer-list and
buffer-predicate parameters do something special. If the
terminal supports colors, the parameters foreground-color,
background-color, background-mode and
display-type are also meaningful. If the terminal supports
frame transparency, the parameter alpha is also meaningful.
These functions let you read and change the parameter values of a frame.
This function returns the value of the parameter parameter (a symbol) of frame. If frame is
nil, it returns the selected frame's parameter. If frame has no setting for parameter, this function returnsnil.
The function
frame-parametersreturns an alist listing all the parameters of frame and their values. If frame isnilor omitted, this returns the selected frame's parameters
This function alters the frame frame based on the elements of alist. Each element of alist has the form
(parm.value), where parm is a symbol naming a parameter. If you don't mention a parameter in alist, its value doesn't change. If frame isnil, it defaults to the selected frame.Some parameters are only meaningful for frames on certain kinds of display (see Frames). If alist includes parameters that are not meaningful for the frame's display, this function will change its value in the frame's parameter list, but will otherwise ignore it.
When alist specifies more than one parameter whose value can affect the new size of frame, the final size of the frame may differ according to the toolkit used. For example, specifying that a frame should from now on have a menu and/or tool bar instead of none and simultaneously specifying the new height of the frame will inevitably lead to a recalculation of the frame's height. Conceptually, in such case, this function will try to have the explicit height specification prevail. It cannot be excluded, however, that the addition (or removal) of the menu or tool bar, when eventually performed by the toolkit, will defeat this intention.
Sometimes, binding
frame-inhibit-implied-resize(see Implied Frame Resizing) to a non-nilvalue around calls to this function may fix the problem sketched here. Sometimes, however, exactly such binding may be hit by the problem.
This function sets the frame parameter parm to the specified value. If frame is
nil, it defaults to the selected frame.
This function alters the frame parameters of all existing frames according to alist, then modifies
default-frame-alist(and, if necessary,initial-frame-alist) to apply the same parameter values to frames that will be created henceforth.
You can specify the parameters for the initial startup frame by
setting initial-frame-alist in your init file (see Init File).
This variable's value is an alist of parameter values used when creating the initial frame. You can set this variable to specify the appearance of the initial frame without altering subsequent frames. Each element has the form:
(parameter . value)Emacs creates the initial frame before it reads your init file. After reading that file, Emacs checks
initial-frame-alist, and applies the parameter settings in the altered value to the already created initial frame.If these settings affect the frame geometry and appearance, you'll see the frame appear with the wrong ones and then change to the specified ones. If that bothers you, you can specify the same geometry and appearance with X resources; those do take effect before the frame is created. See X Resources.
X resource settings typically apply to all frames. If you want to specify some X resources solely for the sake of the initial frame, and you don't want them to apply to subsequent frames, here's how to achieve this. Specify parameters in
default-frame-alistto override the X resources for subsequent frames; then, to prevent these from affecting the initial frame, specify the same parameters ininitial-frame-alistwith values that match the X resources.
If these parameters include (minibuffer . nil), that indicates
that the initial frame should have no minibuffer. In this case, Emacs
creates a separate minibuffer-only frame as well.
This variable's value is an alist of parameter values used when creating an initial minibuffer-only frame (i.e., the minibuffer-only frame that Emacs creates if
initial-frame-alistspecifies a frame with no minibuffer).
This is an alist specifying default values of frame parameters for all Emacs frames—the first frame, and subsequent frames. When using the X Window System, you can get the same results by means of X resources in many cases.
Setting this variable does not affect existing frames. Furthermore, functions that display a buffer in a separate frame may override the default parameters by supplying their own parameters.
If you invoke Emacs with command-line options that specify frame
appearance, those options take effect by adding elements to either
initial-frame-alist or default-frame-alist. Options
which affect just the initial frame, such as `--geometry' and
`--maximized', add to initial-frame-alist; the others add
to default-frame-alist. see Command Line Arguments for Emacs Invocation.
Just what parameters a frame has depends on what display mechanism
it uses. This section describes the parameters that have special
meanings on some or all kinds of terminals. Of these, name,
title, height, width, buffer-list and
buffer-predicate provide meaningful information in terminal
frames, and tty-color-mode is meaningful only for frames on
text terminals.
These frame parameters give the most basic information about the
frame. title and name are meaningful on all terminals.
displaydisplay-typecolor, grayscale or
mono.
titlenil title, it appears in the window
system's title bar at the top of the frame, and also in the mode line
of windows in that frame if mode-line-frame-identification uses
`%F' (see %-Constructs). This is normally the case when
Emacs is not using a window system, and can only display one frame at
a time. See Frame Titles.
nametitle parameter is unspecified or nil. If
you don't specify a name, Emacs sets the frame name automatically
(see Frame Titles).
If you specify the frame name explicitly when you create the frame, the
name is also used (instead of the name of the Emacs executable) when
looking up X resources for the frame.
explicit-namenil.
Position parameters' values are measured in pixels. (Note that none of these parameters exist on TTY frames.)
left(+ pos)
(- pos)
Some window managers ignore program-specified positions. If you want to
be sure the position you specify is not ignored, specify a
non-nil value for the user-position parameter as well.
If the window manager refuses to align a frame at the left or top screen
edge, combining position notation and user-position as in
(modify-frame-parameters
nil '((user-position . t) (left . (+ -4))))
may help to override that.
topleft, except vertically instead of horizontally.
icon-lefticon-top and vice versa.
icon-topuser-positionleft and top parameters, use this parameter to say whether
the specified position was user-specified (explicitly requested in some
way by a human user) or merely program-specified (chosen by a program).
A non-nil value says the position was user-specified.
Window managers generally heed user-specified positions, and some heed
program-specified positions too. But many ignore program-specified
positions, placing the window in a default fashion or letting the user
place it with the mouse. Some window managers, including twm,
let the user specify whether to obey program-specified positions or
ignore them.
When you call make-frame, you should specify a non-nil
value for this parameter if the values of the left and top
parameters represent the user's stated preference; otherwise, use
nil.
Frame parameters specify frame sizes in character units. On
graphical displays, the default face determines the actual
pixel sizes of these character units (see Face Attributes).
heightwidthuser-sizeheight and width what
the user-position parameter (see user-position) does for the position parameters top and
left.
fullscreenfullwidth, fullheight,
fullboth, or maximized. A fullwidth frame is as
wide as possible, a fullheight frame is as tall as possible, and
a fullboth frame is both as wide and as tall as possible. A
maximized frame is like a “fullboth” frame, except that it usually
keeps its title bar and the buttons for resizing
and closing the frame. Also, maximized frames typically avoid hiding
any task bar or panels displayed on the desktop. A “fullboth” frame,
on the other hand, usually omits the title bar and occupies the entire
available screen space.
Full-height and full-width frames are more similar to maximized frames in this regard. However, these typically display an external border which might be absent with maximized frames. Hence the heights of maximized and full-height frames and the widths of maximized and full-width frames often differ by a few pixels.
With some window managers you may have to customize the variable
frame-resize-pixelwise (see Size and Position) in order to
make a frame truly appear maximized or full-screen. Moreover,
some window managers might not support smooth transition between the
various full-screen or maximization states. Customizing the variable
x-frame-normalize-before-maximize can help to overcome that.
fullscreen-restoretoggle-frame-fullscreen command (see Frame Commands) in the “fullboth” state.
Normally this parameter is installed automatically by that command when
toggling the state to fullboth. If, however, you start Emacs in the
“fullboth” state, you have to specify the desired behavior in your initial
file as, for example
(setq default-frame-alist
'((fullscreen . fullboth) (fullscreen-restore . fullheight)))
This will give a new frame full height after typing in it <F11> for the first time.
These frame parameters enable or disable various parts of the frame, or control their sizes.
border-widthinternal-border-widthvertical-scroll-barsleft,
right, and nil for no scroll bars.
horizontal-scroll-barst and
bottom mean yes, nil means no).
scroll-bar-widthnil meaning to
use the default width.
scroll-bar-heightnil meaning
to use the default height.
left-fringeright-fringeWhen you use frame-parameter to query the value of either of
these two frame parameters, the return value is always an integer.
When using set-frame-parameter, passing a nil value
imposes an actual default value of 8 pixels.
right-divider-widthbottom-divider-widthmenu-bar-linestool-bar-linestool-bar-positiontop, bottom left, right.
The default is top.
line-spacingThese frame parameters, meaningful on all kinds of terminals, deal with which buffers have been, or should, be displayed in the frame.
minibuffert means
yes, nil means no, only means this frame is just a
minibuffer. If the value is a minibuffer window (in some other
frame), the frame uses that minibuffer.
This frame parameter takes effect when the frame is created, and can not be changed afterwards.
buffer-predicateother-buffer uses this predicate (from the selected frame) to
decide which buffers it should consider, if the predicate is not
nil. It calls the predicate with one argument, a buffer, once for
each buffer; if the predicate returns a non-nil value, it
considers that buffer.
buffer-listunsplittablenil, this frame's window is never split automatically.
The following frame parameters control various aspects of the frame's interaction with the window manager. They have no effect on text terminals.
visibilitynil for invisible, t for visible, and icon for
iconified. See Visibility of Frames.
auto-raisenil, Emacs automatically raises the frame when it is
selected. Some window managers do not allow this.
auto-lowernil, Emacs automatically lowers the frame when it is
deselected. Some window managers do not allow this.
icon-typenil specifies
no icon (in which case the window manager decides what to show); any
other non-nil value specifies the default Emacs icon.
icon-namenil, the frame's title is used.
window-idouter-window-idwindow-id, changing this parameter has no
actual effect.
wait-for-wmnil, tell Xt to wait for the window manager to confirm
geometry changes. Some window managers, including versions of Fvwm2
and KDE, fail to confirm, so Xt hangs. Set this to nil to
prevent hanging with those window managers.
stickynil, the frame is visible on all virtual desktops on systems
with virtual desktops.
This frame parameter controls the way the cursor looks.
cursor-typeboxhollownilbar(bar . width)
hbar(hbar . height)
The cursor-type frame parameter may be overridden by the
variables cursor-type and
cursor-in-non-selected-windows:
This buffer-local variable controls how the cursor looks in a selected window showing the buffer. If its value is
t, that means to use the cursor specified by thecursor-typeframe parameter. Otherwise, the value should be one of the cursor types listed above, and it overrides thecursor-typeframe parameter.
This buffer-local variable controls how the cursor looks in a window that is not selected. It supports the same values as the
cursor-typeframe parameter; also,nilmeans don't display a cursor in nonselected windows, andt(the default) means use a standard modification of the usual cursor type (solid box becomes hollow box, and bar becomes a narrower bar).
This variable controls the width of the block cursor displayed on extra-wide glyphs such as a tab or a stretch of white space. By default, the block cursor is only as wide as the font's default character, and will not cover all of the width of the glyph under it if that glyph is extra-wide. A non-
nilvalue of this variable means draw the block cursor as wide as the glyph under it. The default value isnil.This variable has no effect on text-mode frames, since the text-mode cursor is drawn by the terminal out of Emacs's control.
This variable specifies how to blink the cursor. Each element has the form
(on-state.off-state). Whenever the cursor type equals on-state (comparing usingequal), the corresponding off-state specifies what the cursor looks like when it blinks off. Both on-state and off-state should be suitable values for thecursor-typeframe parameter.There are various defaults for how to blink each type of cursor, if the type is not mentioned as an on-state here. Changes in this variable do not take effect immediately, only when you specify the
cursor-typeframe parameter.
These frame parameters control the use of fonts and colors.
font-backendx (the X core font
driver) and xft (the Xft font driver). On MS-Windows, there are
currently two available font backends: gdi and
uniscribe (see Windows Fonts). On other systems, there is only one available font backend,
so it does not make sense to modify this frame parameter.
background-modedark or light, according
to whether the background color is a light one or a dark one.
tty-color-mode(tty-color-mode . 8) specifies use of the
ANSI escape sequences for 8 standard text colors. A value of -1 turns
off color support.
If the parameter's value is a symbol, it specifies a number through
the value of tty-color-mode-alist, and the associated number is
used instead.
screen-gammaUsual PC monitors have a screen gamma of 2.2, so color values in
Emacs, and in X windows generally, are calibrated to display properly
on a monitor with that gamma value. If you specify 2.2 for
screen-gamma, that means no correction is needed. Other values
request correction, designed to make the corrected colors appear on
your screen the way they would have appeared without correction on an
ordinary monitor with a gamma value of 2.2.
If your monitor displays colors too light, you should specify a
screen-gamma value smaller than 2.2. This requests correction
that makes colors darker. A screen gamma value of 1.5 may give good
results for LCD color displays.
alphanil value, which tells
Emacs not to set the frame opacity (leaving it to the window manager).
To prevent the frame from disappearing completely from view, the
variable frame-alpha-lower-limit defines a lower opacity limit.
If the value of the frame parameter is less than the value of this
variable, Emacs uses the latter. By default,
frame-alpha-lower-limit is 20.
The alpha frame parameter can also be a cons cell
(active . inactive), where active is the
opacity of the frame when it is selected, and inactive is the
opacity when it is not selected.
The following frame parameters are semi-obsolete in that they are automatically equivalent to particular face attributes of particular faces (see Standard Faces):
fontfont
attribute of the default face.
foreground-color:foreground attribute of the default face.
background-color:background attribute of the default face.
mouse-color:background
attribute of the mouse face.
cursor-color:background attribute of the cursor face.
border-color:background attribute of the border face.
scroll-bar-foregroundnil, the color for the foreground of scroll bars. It is
equivalent to the :foreground attribute of the
scroll-bar face.
scroll-bar-backgroundnil, the color for the background of scroll bars. It is
equivalent to the :background attribute of the
scroll-bar face.
Here's how to examine the data in an X-style window geometry specification:
The function
x-parse-geometryconverts a standard X window geometry string to an alist that you can use as part of the argument tomake-frame.The alist describes which parameters were specified in geom, and gives the values specified for them. Each element looks like
(parameter.value). The possible parameter values areleft,top,width, andheight.For the size parameters, the value must be an integer. The position parameter names
leftandtopare not totally accurate, because some values indicate the position of the right or bottom edges instead. The value possibilities for the position parameters are: an integer, a list(+pos), or a list(-pos); as previously described (see Position Parameters).Here is an example:
(x-parse-geometry "35x70+0-0") => ((height . 70) (width . 35) (top - 0) (left . 0))
Each terminal has a list of associated parameters. These terminal parameters are mostly a convenient way of storage for terminal-local variables, but some terminal parameters have a special meaning.
This section describes functions to read and change the parameter values
of a terminal. They all accept as their argument either a terminal or
a frame; the latter means use that frame's terminal. An argument of
nil means the selected frame's terminal.
This function returns an alist listing all the parameters of terminal and their values.
This function returns the value of the parameter parameter (a symbol) of terminal. If terminal has no setting for parameter, this function returns
nil.
This function sets the parameter parameter of terminal to the specified value, and returns the previous value of that parameter.
Here's a list of a few terminal parameters that have a special meaning:
background-modelight or dark.
normal-erase-is-backspacenormal-erase-is-backspace-mode is turned on or off on this
terminal. See DEL Does Not Delete.
terminal-inittedtty-mode-set-stringstty-setup-hook), explicitly output the necessary escape
sequence using send-string-to-terminal in addition to adding
the sequence to tty-mode-set-strings.
tty-mode-reset-stringstty-mode-set-strings. Emacs emits these strings when
exiting, deleting a terminal, or suspending itself.
Every frame has a name parameter; this serves as the default
for the frame title which window systems typically display at the top of
the frame. You can specify a name explicitly by setting the name
frame property.
Normally you don't specify the name explicitly, and Emacs computes the
frame name automatically based on a template stored in the variable
frame-title-format. Emacs recomputes the name each time the
frame is redisplayed.
This variable specifies how to compute a name for a frame when you have not explicitly specified one. The variable's value is actually a mode line construct, just like
mode-line-format, except that the `%c' and `%l' constructs are ignored. See Mode Line Data.
This variable specifies how to compute the name for an iconified frame, when you have not explicitly specified the frame title. This title appears in the icon itself.
This variable is set automatically by Emacs. Its value is
twhen there are two or more frames (not counting minibuffer-only frames or invisible frames). The default value offrame-title-formatusesmultiple-framesso as to put the buffer name in the frame title only when there is more than one frame.The value of this variable is not guaranteed to be accurate except while processing
frame-title-formatoricon-title-format.
A live frame is one that has not been deleted. When a frame is deleted, it is removed from its terminal display, although it may continue to exist as a Lisp object until there are no more references to it.
This function deletes the frame frame. Unless frame is a tooltip, it first runs the hook
delete-frame-functions(each function gets one argument, frame). By default, frame is the selected frame.A frame cannot be deleted as long as its minibuffer serves as surrogate minibuffer for another frame (see Minibuffers and Frames). Normally, you cannot delete a frame if all other frames are invisible, but if force is non-
nil, then you are allowed to do so.
The function
frame-live-preturns non-nilif the frame frame has not been deleted. The possible non-nilreturn values are like those offramep. See Frames.
Some window managers provide a command to delete a window. These work
by sending a special message to the program that operates the window.
When Emacs gets one of these commands, it generates a
delete-frame event, whose normal definition is a command that
calls the function delete-frame. See Misc Events.
This function returns a list of all the live frames, i.e., those that have not been deleted. It is analogous to
buffer-listfor buffers, and includes frames on all terminals. The list that you get is newly created, so modifying the list doesn't have any effect on the internals of Emacs.
This function returns a list of just the currently visible frames. See Visibility of Frames. Frames on text terminals always count as visible, even though only the selected one is actually displayed.
This function lets you cycle conveniently through all the frames on the current display from an arbitrary starting point. It returns the next frame after frame in the cycle. If frame is omitted or
nil, it defaults to the selected frame (see Input Focus).The second argument, minibuf, says which frames to consider:
nil- Exclude minibuffer-only frames.
visible- Consider all visible frames.
- 0
- Consider all visible or iconified frames.
- a window
- Consider only the frames using that particular window as their minibuffer.
- anything else
- Consider all frames.
Like
next-frame, but cycles through all frames in the opposite direction.
See also next-window and previous-window, in Cyclic Window Ordering.
Normally, each frame has its own minibuffer window at the bottom, which
is used whenever that frame is selected. If the frame has a minibuffer,
you can get it with minibuffer-window (see Definition of minibuffer-window).
However, you can also create a frame without a minibuffer. Such a frame
must use the minibuffer window of some other frame. That other frame
will serve as surrogate minibuffer frame for this frame and cannot
be deleted via delete-frame (see Deleting Frames) as long as
this frame is live.
When you create the frame, you can explicitly specify the minibuffer
window to use (in some other frame). If you don't, then the minibuffer
is found in the frame which is the value of the variable
default-minibuffer-frame. Its value should be a frame that does
have a minibuffer.
If you use a minibuffer-only frame, you might want that frame to raise
when you enter the minibuffer. If so, set the variable
minibuffer-auto-raise to t. See Raising and Lowering.
This variable specifies the frame to use for the minibuffer window, by default. It does not affect existing frames. It is always local to the current terminal and cannot be buffer-local. See Multiple Terminals.
At any time, one frame in Emacs is the selected frame. The selected window always resides on the selected frame.
When Emacs displays its frames on several terminals (see Multiple Terminals), each terminal has its own selected frame. But only one of these is the selected frame: it's the frame that belongs to the terminal from which the most recent input came. That is, when Emacs runs a command that came from a certain terminal, the selected frame is the one of that terminal. Since Emacs runs only a single command at any given time, it needs to consider only one selected frame at a time; this frame is what we call the selected frame in this manual. The display on which the selected frame is shown is the selected frame's display.
Some window systems and window managers direct keyboard input to the
window object that the mouse is in; others require explicit clicks or
commands to shift the focus to various window objects. Either
way, Emacs automatically keeps track of which frame has the focus. To
explicitly switch to a different frame from a Lisp function, call
select-frame-set-input-focus.
Lisp programs can also switch frames temporarily by calling the
function select-frame. This does not alter the window system's
concept of focus; rather, it escapes from the window manager's control
until that control is somehow reasserted.
When using a text terminal, only one frame can be displayed at a time
on the terminal, so after a call to select-frame, the next
redisplay actually displays the newly selected frame. This frame
remains selected until a subsequent call to select-frame. Each
frame on a text terminal has a number which appears in the mode line
before the buffer name (see Mode Line Variables).
This function selects frame, raises it (should it happen to be obscured by other frames) and tries to give it the X server's focus. On a text terminal, the next redisplay displays the new frame on the entire terminal screen. The optional argument norecord has the same meaning as for
select-frame(see below). The return value of this function is not significant.
This function selects frame frame, temporarily disregarding the focus of the X server if any. The selection of frame lasts until the next time the user does something to select a different frame, or until the next time this function is called. (If you are using a window system, the previously selected frame may be restored as the selected frame after return to the command loop, because it still may have the window system's input focus.)
The specified frame becomes the selected frame, and its terminal becomes the selected terminal. This function then calls
select-windowas a subroutine, passing the window selected within frame as its first argument and norecord as its second argument (hence, if norecord is non-nil, this avoids changing the order of recently selected windows nor the buffer list). See Selecting Windows.This function returns frame, or
nilif frame has been deleted.In general, you should never use
select-framein a way that could switch to a different terminal without switching back when you're done.
Emacs cooperates with the window system by arranging to select frames as
the server and window manager request. It does so by generating a
special kind of input event, called a focus event, when
appropriate. The command loop handles a focus event by calling
handle-switch-frame. See Focus Events.
This function handles a focus event by selecting frame frame.
Focus events normally do their job by invoking this command. Don't call it for any other reason.
This function redirects focus from frame to focus-frame. This means that focus-frame will receive subsequent keystrokes and events intended for frame. After such an event, the value of
last-event-framewill be focus-frame. Also, switch-frame events specifying frame will instead select focus-frame.If focus-frame is omitted or
nil, that cancels any existing redirection for frame, which therefore once again receives its own events.One use of focus redirection is for frames that don't have minibuffers. These frames use minibuffers on other frames. Activating a minibuffer on another frame redirects focus to that frame. This puts the focus on the minibuffer's frame, where it belongs, even though the mouse remains in the frame that activated the minibuffer.
Selecting a frame can also change focus redirections. Selecting frame
bar, whenfoohad been selected, changes any redirections pointing tofooso that they point tobarinstead. This allows focus redirection to work properly when the user switches from one frame to another usingselect-window.This means that a frame whose focus is redirected to itself is treated differently from a frame whose focus is not redirected.
select-frameaffects the former but not the latter.The redirection lasts until
redirect-frame-focusis called to change it.
This option is how you inform Emacs whether the window manager transfers focus when the user moves the mouse. Non-
nilsays that it does. When this is so, the commandother-framemoves the mouse to a position consistent with the new selected frame.
A frame on a graphical display may be visible, invisible, or iconified. If it is visible, its contents are displayed in the usual manner. If it is iconified, its contents are not displayed, but there is a little icon somewhere to bring the frame back into view (some window managers refer to this state as minimized rather than iconified, but from Emacs' point of view they are the same thing). If a frame is invisible, it is not displayed at all.
Visibility is meaningless on text terminals, since only the selected one is actually displayed in any case.
This function returns the visibility status of frame frame. The value is
tif frame is visible,nilif it is invisible, andiconif it is iconified.On a text terminal, all frames are considered visible for the purposes of this function, even though only one frame is displayed. See Raising and Lowering.
This function iconifies frame frame. If you omit frame, it iconifies the selected frame.
This function makes frame frame visible. If you omit frame, it makes the selected frame visible. This does not raise the frame, but you can do that with
raise-frameif you wish (see Raising and Lowering).
This function makes frame frame invisible. If you omit frame, it makes the selected frame invisible.
Unless force is non-
nil, this function refuses to make frame invisible if all other frames are invisible..
The visibility status of a frame is also available as a frame parameter. You can read or change it as such. See Management Parameters. The user can also iconify and deiconify frames with the window manager. This happens below the level at which Emacs can exert any control, but Emacs does provide events that you can use to keep track of such changes. See Misc Events.
Most window systems use a desktop metaphor. Part of this metaphor
is the idea that system-level windows (e.g., Emacs frames) are
stacked in a notional third dimension perpendicular to the screen
surface. Where two overlap, the one higher up covers the one
underneath. You can raise or lower a frame using the
functions raise-frame and lower-frame.
This function raises frame frame (default, the selected frame). If frame is invisible or iconified, this makes it visible.
This function lowers frame frame (default, the selected frame).
If this is non-
nil, activation of the minibuffer raises the frame that the minibuffer window is in.
On window systems, you can also enable auto-raising (on frame selection) or auto-lowering (on frame deselection) using frame parameters. See Management Parameters.
The concept of raising and lowering frames also applies to text terminal frames. On each text terminal, only the top frame is displayed at any one time.
This function returns the top frame on terminal. terminal should be a terminal object, a frame (meaning that frame's terminal), or
nil(meaning the selected frame's terminal). If it does not refer to a text terminal, the return value isnil.
A frame configuration records the current arrangement of frames, all their properties, and the window configuration of each one. (See Window Configurations.)
This function returns a frame configuration list that describes the current arrangement of frames and their contents.
This function restores the state of frames described in configuration. However, this function does not restore deleted frames.
Ordinarily, this function deletes all existing frames not listed in configuration. But if nodelete is non-
nil, the unwanted frames are iconified instead.
Sometimes it is useful to track the mouse, which means to display something to indicate where the mouse is and move the indicator as the mouse moves. For efficient mouse tracking, you need a way to wait until the mouse actually moves.
The convenient way to track the mouse is to ask for events to represent mouse motion. Then you can wait for motion by waiting for an event. In addition, you can easily handle any other sorts of events that may occur. That is useful, because normally you don't want to track the mouse forever—only until some other event, such as the release of a button.
This special form executes body, with generation of mouse motion events enabled. Typically, body would use
read-eventto read the motion events and modify the display accordingly. See Motion Events, for the format of mouse motion events.The value of
track-mouseis that of the last form in body. You should design body to return when it sees the up-event that indicates the release of the button, or whatever kind of event means it is time to stop tracking.The
track-mouseform causes Emacs to generate mouse motion events by binding the variabletrack-mouseto a non-nilvalue. If that variable has the special valuedragging, it additionally instructs the display engine to refrain from changing the shape of the mouse pointer. This is desirable in Lisp programs that require mouse dragging across large portions of Emacs display, which might otherwise cause the mouse pointer to change its shape according to the display portion it hovers on (see Pointer Shape). Therefore, Lisp programs that need the mouse pointer to retain its original shape during dragging should bindtrack-mouseto the valuedraggingat the beginning of their body.
The usual purpose of tracking mouse motion is to indicate on the screen the consequences of pushing or releasing a button at the current position.
In many cases, you can avoid the need to track the mouse by using
the mouse-face text property (see Special Properties).
That works at a much lower level and runs more smoothly than
Lisp-level mouse tracking.
The functions mouse-position and set-mouse-position
give access to the current position of the mouse.
This function returns a description of the position of the mouse. The value looks like
(frame x.y), where x and y are integers giving the (possibly rounded) position in multiples of the default character size of frame (see Frame Font) relative to the native position of frame (see Frame Geometry).
If non-
nil, the value of this variable is a function formouse-positionto call.mouse-positioncalls this function just before returning, with its normal return value as the sole argument, and it returns whatever this function returns to it.This abnormal hook exists for the benefit of packages like xt-mouse.el that need to do mouse handling at the Lisp level.
This function warps the mouse to position x, y in frame frame. The arguments x and y are integers, giving the position in multiples of the default character size of frame (see Frame Font) relative to the native position of frame (see Frame Geometry).
The resulting mouse position is constrained to the native frame of frame. If frame is not visible, this function does nothing. The return value is not significant.
This function is like
mouse-positionexcept that it returns coordinates in units of pixels rather than units of characters.
This function warps the mouse like
set-mouse-positionexcept that x and y are in units of pixels rather than units of characters.The resulting mouse position is not constrained to the native frame of frame. If frame is not visible, this function does nothing. The return value is not significant.
On a graphical terminal the following two functions allow the absolute position of the mouse cursor to be retrieved and set.
This function returns a cons cell (x . y) of the coordinates of the mouse cursor position in pixels, relative to a position (0, 0) of the selected frame's display.
This function moves the mouse cursor to the position (x, y). The coordinates x and y are interpreted in pixels relative to a position (0, 0) of the selected frame's display.
The following function can tell whether the mouse cursor is currently visible on a frame:
This predicate function returns non-
nilif the mouse pointer displayed on frame is visible; otherwise it returnsnil. frame omitted ornilmeans the selected frame. This is useful whenmake-pointer-invisibleis set tot: it allows you to know if the pointer has been hidden. See Mouse Avoidance.
A Lisp program can pop up a menu so that the user can choose an alternative with the mouse. On a text terminal, if the mouse is not available, the user can choose an alternative using the keyboard motion keys—C-n, C-p, or up- and down-arrow keys.
This function displays a pop-up menu and returns an indication of what selection the user makes.
The argument position specifies where on the screen to put the top left corner of the menu. It can be either a mouse button event (which says to put the menu where the user actuated the button) or a list of this form:
((xoffset yoffset) window)where xoffset and yoffset are coordinates, measured in pixels, counting from the top left corner of window. window may be a window or a frame.
If position is
t, it means to use the current mouse position (or the top-left corner of the frame if the mouse is not available on a text terminal). If position isnil, it means to precompute the key binding equivalents for the keymaps specified in menu, without actually displaying or popping up the menu.The argument menu says what to display in the menu. It can be a keymap or a list of keymaps (see Menu Keymaps). In this case, the return value is the list of events corresponding to the user's choice. This list has more than one element if the choice occurred in a submenu. (Note that
x-popup-menudoes not actually execute the command bound to that sequence of events.) On text terminals and toolkits that support menu titles, the title is taken from the prompt string of menu if menu is a keymap, or from the prompt string of the first keymap in menu if it is a list of keymaps (see Defining Menus).Alternatively, menu can have the following form:
(title pane1 pane2...)where each pane is a list of form
(title item1 item2...)Each item should be a cons cell,
(line.value), where line is a string and value is the value to return if that line is chosen. Unlike in a menu keymap, anilvalue does not make the menu item non-selectable. Alternatively, each item can be a string rather than a cons cell; this makes a non-selectable menu item.If the user gets rid of the menu without making a valid choice, for instance by clicking the mouse away from a valid choice or by typing C-g, then this normally results in a quit and
x-popup-menudoes not return. But if position is a mouse button event (indicating that the user invoked the menu with the mouse) then no quit occurs andx-popup-menureturnsnil.
Usage note: Don't use x-popup-menu to display a menu
if you could do the job with a prefix key defined with a menu keymap.
If you use a menu keymap to implement a menu, C-h c and C-h
a can see the individual items in that menu and provide help for them.
If instead you implement the menu by defining a command that calls
x-popup-menu, the help facilities cannot know what happens inside
that command, so they cannot give any help for the menu's items.
The menu bar mechanism, which lets you switch between submenus by
moving the mouse, cannot look within the definition of a command to see
that it calls x-popup-menu. Therefore, if you try to implement a
submenu using x-popup-menu, it cannot work with the menu bar in
an integrated fashion. This is why all menu bar submenus are
implemented with menu keymaps within the parent menu, and never with
x-popup-menu. See Menu Bar.
If you want a menu bar submenu to have contents that vary, you should
still use a menu keymap to implement it. To make the contents vary, add
a hook function to menu-bar-update-hook to update the contents of
the menu keymap as necessary.
A dialog box is a variant of a pop-up menu—it looks a little
different, it always appears in the center of a frame, and it has just
one level and one or more buttons. The main use of dialog boxes is
for asking questions that the user can answer with “yes”, “no”,
and a few other alternatives. With a single button, they can also
force the user to acknowledge important information. The functions
y-or-n-p and yes-or-no-p use dialog boxes instead of the
keyboard, when called from commands invoked by mouse clicks.
This function displays a pop-up dialog box and returns an indication of what selection the user makes. The argument contents specifies the alternatives to offer; it has this format:
(title (string . value)...)which looks like the list that specifies a single pane for
x-popup-menu.The return value is value from the chosen alternative.
As for
x-popup-menu, an element of the list may be just a string instead of a cons cell(string.value). That makes a box that cannot be selected.If
nilappears in the list, it separates the left-hand items from the right-hand items; items that precede thenilappear on the left, and items that follow thenilappear on the right. If you don't include anilin the list, then approximately half the items appear on each side.Dialog boxes always appear in the center of a frame; the argument position specifies which frame. The possible values are as in
x-popup-menu, but the precise coordinates or the individual window don't matter; only the frame matters.If header is non-
nil, the frame title for the box is `Information', otherwise it is `Question'. The former is used formessage-box(see message-box). (On text terminals, the box title is not displayed.)In some configurations, Emacs cannot display a real dialog box; so instead it displays the same items in a pop-up menu in the center of the frame.
If the user gets rid of the dialog box without making a valid choice, for instance using the window manager, then this produces a quit and
x-popup-dialogdoes not return.
You can specify the mouse pointer style for particular text or
images using the pointer text property, and for images with the
:pointer and :map image properties. The values you can
use in these properties are text (or nil), arrow,
hand, vdrag, hdrag, modeline, and
hourglass. text stands for the usual mouse pointer
style used over text.
Over void parts of the window (parts that do not correspond to any
of the buffer contents), the mouse pointer usually uses the
arrow style, but you can specify a different style (one of
those above) by setting void-text-area-pointer.
This variable specifies the mouse pointer style for void text areas. These include the areas after the end of a line or below the last line in the buffer. The default is to use the
arrow(non-text) pointer style.
When using X, you can specify what the text pointer style
really looks like by setting the variable x-pointer-shape.
This variable specifies the pointer shape to use ordinarily in the Emacs frame, for the
textpointer style.
This variable specifies the pointer shape to use when the mouse is over mouse-sensitive text.
These variables affect newly created frames. They do not normally affect existing frames; however, if you set the mouse color of a frame, that also installs the current value of those two variables. See Font and Color Parameters.
The values you can use, to specify either of these pointer shapes, are defined in the file lisp/term/x-win.el. Use M-x apropos <RET> x-pointer <RET> to see a list of them.
In window systems, such as X, data can be transferred between different applications by means of selections. X defines an arbitrary number of selection types, each of which can store its own data; however, only three are commonly used: the clipboard, primary selection, and secondary selection. Other window systems support only the clipboard. See Cut and Paste, for Emacs commands that make use of these selections. This section documents the low-level functions for reading and setting window-system selections.
This function sets a window-system selection. It takes two arguments: a selection type type, and the value to assign to it, data.
type should be a symbol; it is usually one of
PRIMARY,SECONDARYorCLIPBOARD. These are symbols with upper-case names, in accord with X Window System conventions. If type isnil, that stands forPRIMARY.If data is
nil, it means to clear out the selection. Otherwise, data may be a string, a symbol, an integer (or a cons of two integers or list of two integers), an overlay, or a cons of two markers pointing to the same buffer. An overlay or a pair of markers stands for text in the overlay or between the markers. The argument data may also be a vector of valid non-vector selection values.This function returns data.
This function accesses selections set up by Emacs or by other programs. It takes two optional arguments, type and data-type. The default for type, the selection type, is
PRIMARY.The data-type argument specifies the form of data conversion to use, to convert the raw data obtained from another program into Lisp data. Meaningful values include
TEXT,STRING,UTF8_STRING,TARGETS,LENGTH,DELETE,FILE_NAME,CHARACTER_POSITION,NAME,LINE_NUMBER,COLUMN_NUMBER,OWNER_OS,HOST_NAME,USER,CLASS,ATOM, andINTEGER. (These are symbols with upper-case names in accord with X conventions.) The default for data-type isSTRING. Window systems other than X usually support only a small subset of these types, in addition toSTRING.
This variable specifies the coding system to use when reading and writing selections or the clipboard. See Coding Systems. The default is
compound-text-with-extensions, which converts to the text representation that X11 normally uses.
When Emacs runs on MS-Windows, it does not implement X selections in
general, but it does support the clipboard. gui-get-selection
and gui-set-selection on MS-Windows support the text data type
only; if the clipboard holds other types of data, Emacs treats the
clipboard as empty. The supported data type is STRING.
For backward compatibility, there are obsolete aliases
x-get-selection and x-set-selection, which were the
names of gui-get-selection and gui-set-selection before
Emacs 25.1.
When a user drags something from another application over Emacs, that other
application expects Emacs to tell it if Emacs can handle the data that is
dragged. The variable x-dnd-test-function is used by Emacs to determine
what to reply. The default value is x-dnd-default-test-function
which accepts drops if the type of the data to be dropped is present in
x-dnd-known-types. You can customize x-dnd-test-function and/or
x-dnd-known-types if you want Emacs to accept or reject drops based
on some other criteria.
If you want to change the way Emacs handles drop of different types
or add a new type, customize x-dnd-types-alist. This requires
detailed knowledge of what types other applications use for drag and
drop.
When an URL is dropped on Emacs it may be a file, but it may also be
another URL type (ftp, http, etc.). Emacs first checks
dnd-protocol-alist to determine what to do with the URL. If
there is no match there and if browse-url-browser-function is
an alist, Emacs looks for a match there. If no match is found the
text for the URL is inserted. If you want to alter Emacs behavior,
you can customize these variables.
A color name is text (usually in a string) that specifies a color. Symbolic names such as `black', `white', `red', etc., are allowed; use M-x list-colors-display to see a list of defined names. You can also specify colors numerically in forms such as `#rgb' and `RGB:r/g/b', where r specifies the red level, g specifies the green level, and b specifies the blue level. You can use either one, two, three, or four hex digits for r; then you must use the same number of hex digits for all g and b as well, making either 3, 6, 9 or 12 hex digits in all. (See the documentation of the X Window System for more details about numerical RGB specification of colors.)
These functions provide a way to determine which color names are valid, and what they look like. In some cases, the value depends on the selected frame, as described below; see Input Focus, for the meaning of the term “selected frame”.
To read user input of color names with completion, use
read-color (see read-color).
This function reports whether a color name is meaningful. It returns
tif so; otherwise,nil. The argument frame says which frame's display to ask about; if frame is omitted ornil, the selected frame is used.Note that this does not tell you whether the display you are using really supports that color. When using X, you can ask for any defined color on any kind of display, and you will get some result—typically, the closest it can do. To determine whether a frame can really display a certain color, use
color-supported-p(see below).This function used to be called
x-color-defined-p, and that name is still supported as an alias.
This function returns a list of the color names that are defined and supported on frame frame (default, the selected frame). If frame does not support colors, the value is
nil.This function used to be called
x-defined-colors, and that name is still supported as an alias.
This returns
tif frame can really display the color color (or at least something close to it). If frame is omitted ornil, the question applies to the selected frame.Some terminals support a different set of colors for foreground and background. If background-p is non-
nil, that means you are asking whether color can be used as a background; otherwise you are asking whether it can be used as a foreground.The argument color must be a valid color name.
This returns
tif color is a shade of gray, as defined on frame's display. If frame is omitted ornil, the question applies to the selected frame. If color is not a valid color name, this function returnsnil.
This function returns a value that describes what color should ideally look like on frame. If color is defined, the value is a list of three integers, which give the amount of red, the amount of green, and the amount of blue. Each integer ranges in principle from 0 to 65535, but some displays may not use the full range. This three-element list is called the rgb values of the color.
If color is not defined, the value is
nil.(color-values "black") => (0 0 0) (color-values "white") => (65280 65280 65280) (color-values "red") => (65280 0 0) (color-values "pink") => (65280 49152 51968) (color-values "hungry") => nilThe color values are returned for frame's display. If frame is omitted or
nil, the information is returned for the selected frame's display. If the frame cannot display colors, the value isnil.This function used to be called
x-color-values, and that name is still supported as an alias.
Text terminals usually support only a small number of colors, and the computer uses small integers to select colors on the terminal. This means that the computer cannot reliably tell what the selected color looks like; instead, you have to inform your application which small integers correspond to which colors. However, Emacs does know the standard set of colors and will try to use them automatically.
The functions described in this section control how terminal colors are used by Emacs.
Several of these functions use or return rgb values, described in Color Names.
These functions accept a display (either a frame or the name of a terminal) as an optional argument. We hope in the future to make Emacs support different colors on different text terminals; then this argument will specify which terminal to operate on (the default being the selected frame's terminal; see Input Focus). At present, though, the frame argument has no effect.
This function associates the color name name with color number number on the terminal.
The optional argument rgb, if specified, is an rgb value, a list of three numbers that specify what the color actually looks like. If you do not specify rgb, then this color cannot be used by
tty-color-approximateto approximate other colors, because Emacs will not know what it looks like.
This function clears the table of defined colors for a text terminal.
This function returns an alist recording the known colors supported by a text terminal.
Each element has the form
(name number.rgb)or(name number). Here, name is the color name, number is the number used to specify it to the terminal. If present, rgb is a list of three color values (for red, green, and blue) that says what the color actually looks like.
This function finds the closest color, among the known colors supported for display, to that described by the rgb value rgb (a list of color values). The return value is an element of
tty-color-alist.
This function finds the closest color to color among the known colors supported for display and returns its index (an integer). If the name color is not defined, the value is
nil.
This section describes some of the functions and variables for querying and using X resources, or their equivalent on your operating system. See X Resources, for more information about X resources.
The function
x-get-resourceretrieves a resource value from the X Window defaults database.Resources are indexed by a combination of a key and a class. This function searches using a key of the form `instance.attribute' (where instance is the name under which Emacs was invoked), and using `Emacs.class' as the class.
The optional arguments component and subclass add to the key and the class, respectively. You must specify both of them or neither. If you specify them, the key is `instance.component.attribute', and the class is `Emacs.class.subclass'.
This variable specifies the application name that
x-get-resourceshould look up. The default value is"Emacs". You can examine X resources for other application names by binding this variable to some other string, around a call tox-get-resource.
This variable specifies the instance name that
x-get-resourceshould look up. The default value is the name Emacs was invoked with, or the value specified with the `-name' or `-rn' switches.
To illustrate some of the above, suppose that you have the line:
xterm.vt100.background: yellow
in your X resources file (whose name is usually ~/.Xdefaults or ~/.Xresources). Then:
(let ((x-resource-class "XTerm") (x-resource-name "xterm"))
(x-get-resource "vt100.background" "VT100.Background"))
=> "yellow"
(let ((x-resource-class "XTerm") (x-resource-name "xterm"))
(x-get-resource "background" "VT100" "vt100" "Background"))
=> "yellow"
If this variable is non-
nil, Emacs does not look up X resources, and X resources do not have any effect when creating new frames.
The functions in this section describe the basic capabilities of a particular display. Lisp programs can use them to adapt their behavior to what the display can do. For example, a program that ordinarily uses a popup menu could use the minibuffer if popup menus are not supported.
The optional argument display in these functions specifies which
display to ask the question about. It can be a display name, a frame
(which designates the display that frame is on), or nil (which
refers to the selected frame's display, see Input Focus).
See Color Names, Text Terminal Colors, for other functions to obtain information about displays.
This function returns
tif popup menus are supported on display,nilif not. Support for popup menus requires that the mouse be available, since the menu is popped up by clicking the mouse on some portion of the Emacs display.
This function returns
tif display is a graphic display capable of displaying several frames and several different fonts at once. This is true for displays that use a window system such as X, and false for text terminals.
This function returns
tif display has a mouse available,nilif not.
This function returns
tif the screen is a color screen. It used to be calledx-display-color-p, and that name is still supported as an alias.
This function returns
tif the screen can display shades of gray. (All color displays can do this.)
This function returns non-
nilif all the face attributes in attributes are supported (see Face Attributes).The definition of “supported” is somewhat heuristic, but basically means that a face containing all the attributes in attributes, when merged with the default face for display, can be represented in a way that's
- different in appearance than the default face, and
- close in spirit to what the attributes specify, if not exact.
Point (2) implies that a
:weight blackattribute will be satisfied by any display that can display bold, as will:foreground "yellow"as long as some yellowish color can be displayed, but:slant italicwill not be satisfied by the tty display code's automatic substitution of a dim face for italic.
This function returns
tif display supports selections. Windowed displays normally support selections, but they may also be supported in some other cases.
This function returns
tif display can display images. Windowed displays ought in principle to handle images, but some systems lack the support for that. On a display that does not support images, Emacs cannot display a tool bar.
This function returns the number of screens associated with the display.
This function returns the height of the screen in pixels. On a character terminal, it gives the height in characters.
For graphical terminals, note that on multi-monitor setups this refers to the pixel height for all physical monitors associated with display. See Multiple Terminals.
This function returns the width of the screen in pixels. On a character terminal, it gives the width in characters.
For graphical terminals, note that on multi-monitor setups this refers to the pixel width for all physical monitors associated with display. See Multiple Terminals.
This function returns the height of the screen in millimeters, or
nilif Emacs cannot get that information.For graphical terminals, note that on multi-monitor setups this refers to the height for all physical monitors associated with display. See Multiple Terminals.
This function returns the width of the screen in millimeters, or
nilif Emacs cannot get that information.For graphical terminals, note that on multi-monitor setups this refers to the width for all physical monitors associated with display. See Multiple Terminals.
This variable allows the user to specify the dimensions of graphical displays returned by
display-mm-heightanddisplay-mm-widthin case the system provides incorrect values.
This function returns the backing store capability of the display. Backing store means recording the pixels of windows (and parts of windows) that are not exposed, so that when exposed they can be displayed very quickly.
Values can be the symbols
always,when-mapped, ornot-useful. The function can also returnnilwhen the question is inapplicable to a certain kind of display.
This function returns non-
nilif the display supports the SaveUnder feature. That feature is used by pop-up windows to save the pixels they obscure, so that they can pop down quickly.
This function returns the number of planes the display supports. This is typically the number of bits per pixel. For a tty display, it is log to base two of the number of colors supported.
This function returns the visual class for the screen. The value is one of the symbols
static-gray(a limited, unchangeable number of grays),gray-scale(a full range of grays),static-color(a limited, unchangeable number of colors),pseudo-color(a limited number of colors),true-color(a full range of colors), anddirect-color(a full range of colors).
This function returns the number of color cells the screen supports.
These functions obtain additional information about the window
system in use where Emacs shows the specified display. (Their
names begin with x- for historical reasons.)
This function returns the list of version numbers of the GUI window system running on display, such as the X server on GNU and Unix systems. The value is a list of three integers: the major and minor version numbers of the protocol, and the distributor-specific release number of the window system software itself. On GNU and Unix systems, these are normally the version of the X protocol and the distributor-specific release number of the X server software. On MS-Windows, this is the version of the Windows OS.
This function returns the vendor that provided the window system software (as a string). On GNU and Unix systems this really means whoever distributes the X server. On MS-Windows this is the vendor ID string of the Windows OS (Microsoft).
When the developers of X labeled software distributors as “vendors”, they showed their false assumption that no system could ever be developed and distributed noncommercially.
A position is the index of a character in the text of a buffer. More precisely, a position identifies the place between two characters (or before the first character, or after the last character), so we can speak of the character before or after a given position. However, we often speak of the character “at” a position, meaning the character after that position.
Positions are usually represented as integers starting from 1, but can also be represented as markers—special objects that relocate automatically when text is inserted or deleted so they stay with the surrounding characters. Functions that expect an argument to be a position (an integer), but accept a marker as a substitute, normally ignore which buffer the marker points into; they convert the marker to an integer, and use that integer, exactly as if you had passed the integer as the argument, even if the marker points to the wrong buffer. A marker that points nowhere cannot convert to an integer; using it instead of an integer causes an error. See Markers.
See also the field feature (see Fields), which provides functions that are used by many cursor-motion commands.
Point is a special buffer position used by many editing commands, including the self-inserting typed characters and text insertion functions. Other commands move point through the text to allow editing and insertion at different places.
Like other positions, point designates a place between two characters (or before the first character, or after the last character), rather than a particular character. Usually terminals display the cursor over the character that immediately follows point; point is actually before the character on which the cursor sits.
The value of point is a number no less than 1, and no greater than the buffer size plus 1. If narrowing is in effect (see Narrowing), then point is constrained to fall within the accessible portion of the buffer (possibly at one end of it).
Each buffer has its own value of point, which is independent of the value of point in other buffers. Each window also has a value of point, which is independent of the value of point in other windows on the same buffer. This is why point can have different values in various windows that display the same buffer. When a buffer appears in only one window, the buffer's point and the window's point normally have the same value, so the distinction is rarely important. See Window Point, for more details.
This function returns the value of point in the current buffer, as an integer.
(point) => 175
This function returns the minimum accessible value of point in the current buffer. This is normally 1, but if narrowing is in effect, it is the position of the start of the region that you narrowed to. (See Narrowing.)
This function returns the maximum accessible value of point in the current buffer. This is
(1+ (buffer-size)), unless narrowing is in effect, in which case it is the position of the end of the region that you narrowed to. (See Narrowing.)
This function returns
(point-max)if flag is greater than 0,(point-min)otherwise. The argument flag must be a number.
This function returns the total number of characters in the current buffer. In the absence of any narrowing (see Narrowing),
point-maxreturns a value one larger than this.If you specify a buffer, buffer, then the value is the size of buffer.
(buffer-size) => 35 (point-max) => 36
Motion functions change the value of point, either relative to the current value of point, relative to the beginning or end of the buffer, or relative to the edges of the selected window. See Point.
These functions move point based on a count of characters.
goto-char is the fundamental primitive; the other functions use
that.
This function sets point in the current buffer to the value position.
If narrowing is in effect, position still counts from the beginning of the buffer, but point cannot go outside the accessible portion. If position is out of range,
goto-charmoves point to the beginning or the end of the accessible portion.When this function is called interactively, position is the numeric prefix argument, if provided; otherwise it is read from the minibuffer.
goto-charreturns position.
This function moves point count characters forward, towards the end of the buffer (or backward, towards the beginning of the buffer, if count is negative). If count is
nil, the default is 1.If this attempts to move past the beginning or end of the buffer (or the limits of the accessible portion, when narrowing is in effect), it signals an error with error symbol
beginning-of-bufferorend-of-buffer.In an interactive call, count is the numeric prefix argument.
This is just like
forward-charexcept that it moves in the opposite direction.
The functions for parsing words described below use the syntax table to decide whether a given character is part of a word. See Syntax Tables.
This function moves point forward count words (or backward if count is negative). If count is omitted or
nil, it defaults to 1. In an interactive call, count is specified by the numeric prefix argument.“Moving one word” means moving until point crosses a word-constituent character, which indicates the beginning of a word, and then continue moving until the word ends. By default, characters that begin and end words, known as word boundaries, are defined by the current buffer's syntax table (see Syntax Class Table), but modes can override that by setting up a suitable
find-word-boundary-function-table, described below. In any case, this function cannot move point past the boundary of the accessible portion of the buffer, or across a field boundary (see Fields). The most common case of a field boundary is the end of the prompt in the minibuffer.If it is possible to move count words, without being stopped prematurely by the buffer boundary or a field boundary, the value is
t. Otherwise, the return value isniland point stops at the buffer boundary or field boundary.If
inhibit-field-text-motionis non-nil, this function ignores field boundaries.
This function is just like
forward-word, except that it moves backward until encountering the front of a word, rather than forward.
This variable affects the behavior of
forward-wordandbackward-word, and everything that uses them. If it is non-nil, then characters in the escape and character-quote syntax classes count as part of words. Otherwise, they do not.
If this variable is non-
nil, certain motion functions includingforward-word,forward-sentence, andforward-paragraphignore field boundaries.
This variable affects the behavior of
forward-wordandbackward-word, and everything that uses them. Its value is a char-table (see Char-Tables) of functions to search for word boundaries. If a character has a non-nilentry in this table, then when a word starts or ends with that character, the corresponding function will be called with 2 arguments: pos and limit. The function should return the position of the other word boundary. Specifically, if pos is smaller than limit, then pos is at the beginning of a word, and the function should return the position after the last character of the word; otherwise, pos is at the last character of a word, and the function should return the position of that word's first character.
This function is like
forward-word, but it is not affected byfind-word-boundary-function-table. Lisp programs that should not change behavior when word movement is modified by modes which set that table, such assubword-mode, should use this function instead offorward-word.
This function is like
backward-word, but it is not affected byfind-word-boundary-function-table. Like withforward-word-strictly, use this function instead ofbackward-wordwhen movement by words should only consider syntax tables.
To move point to the beginning of the buffer, write:
(goto-char (point-min))
Likewise, to move to the end of the buffer, use:
(goto-char (point-max))
Here are two commands that users use to do these things. They are documented here to warn you not to use them in Lisp programs, because they set the mark and display messages in the echo area.
This function moves point to the beginning of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position (except in Transient Mark mode, if the mark is already active, it does not set the mark.)
If n is non-
nil, then it puts point n tenths of the way from the beginning of the accessible portion of the buffer. In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults tonil.Warning: Don't use this function in Lisp programs!
This function moves point to the end of the buffer (or the limits of the accessible portion, when narrowing is in effect), setting the mark at the previous position (except in Transient Mark mode when the mark is already active). If n is non-
nil, then it puts point n tenths of the way from the end of the accessible portion of the buffer.In an interactive call, n is the numeric prefix argument, if provided; otherwise n defaults to
nil.Warning: Don't use this function in Lisp programs!
Text lines are portions of the buffer delimited by newline characters, which are regarded as part of the previous line. The first text line begins at the beginning of the buffer, and the last text line ends at the end of the buffer whether or not the last character is a newline. The division of the buffer into text lines is not affected by the width of the window, by line continuation in display, or by how tabs and control characters are displayed.
This function moves point to the beginning of the current line. With an argument count not
nilor 1, it moves forward count−1 lines and then to the beginning of the line.This function does not move point across a field boundary (see Fields) unless doing so would move beyond there to a different line; therefore, if count is
nilor 1, and point starts at a field boundary, point does not move. To ignore field boundaries, either bindinhibit-field-text-motiontot, or use theforward-linefunction instead. For instance,(forward-line 0)does the same thing as(beginning-of-line), except that it ignores field boundaries.If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
Return the position that
(beginning-of-linecount)would move to.
This function moves point to the end of the current line. With an argument count not
nilor 1, it moves forward count−1 lines and then to the end of the line.This function does not move point across a field boundary (see Fields) unless doing so would move beyond there to a different line; therefore, if count is
nilor 1, and point starts at a field boundary, point does not move. To ignore field boundaries, bindinhibit-field-text-motiontot.If this function reaches the end of the buffer (or of the accessible portion, if narrowing is in effect), it positions point there. No error is signaled.
Return the position that
(end-of-linecount)would move to.
This function moves point forward count lines, to the beginning of the line following that. If count is negative, it moves point −count lines backward, to the beginning of a line preceding that. If count is zero, it moves point to the beginning of the current line. If count is
nil, that means 1.If
forward-lineencounters the beginning or end of the buffer (or of the accessible portion) before finding that many lines, it sets point there. No error is signaled.
forward-linereturns the difference between count and the number of lines actually moved. If you attempt to move down five lines from the beginning of a buffer that has only three lines, point stops at the end of the last line, and the value will be 2. As an explicit exception, if the last accessible line is non-empty, but has no newline (e.g., if the buffer ends without a newline), the function sets point to the end of that line, and the value returned by the function counts that line as one line successfully moved.In an interactive call, count is the numeric prefix argument.
This function returns the number of lines between the positions start and end in the current buffer. If start and end are equal, then it returns 0. Otherwise it returns at least 1, even if start and end are on the same line. This is because the text between them, considered in isolation, must contain at least one line unless it is empty.
This function returns the number of words between the positions start and end in the current buffer.
This function can also be called interactively. In that case, it prints a message reporting the number of lines, words, and characters in the buffer, or in the region if the region is active.
This function returns the line number in the current buffer corresponding to the buffer position pos. If pos is
nilor omitted, the current buffer position is used.
Also see the functions bolp and eolp in Near Point.
These functions do not move point, but test whether it is already at the
beginning or end of a line.
The line functions in the previous section count text lines, delimited only by newline characters. By contrast, these functions count screen lines, which are defined by the way the text appears on the screen. A text line is a single screen line if it is short enough to fit the width of the selected window, but otherwise it may occupy several screen lines.
In some cases, text lines are truncated on the screen rather than
continued onto additional screen lines. In these cases,
vertical-motion moves point much like forward-line.
See Truncation.
Because the width of a given string depends on the flags that control
the appearance of certain characters, vertical-motion behaves
differently, for a given piece of text, depending on the buffer it is
in, and even on the selected window (because the width, the truncation
flag, and display table may vary between windows). See Usual Display.
These functions scan text to determine where screen lines break, and thus take time proportional to the distance scanned.
This function moves point to the start of the screen line count screen lines down from the screen line containing point. If count is negative, it moves up instead.
The count argument can be a cons cell,
(cols.lines), instead of an integer. Then the function moves by lines screen lines, and puts point cols columns from the visual start of that screen line. Note that cols are counted from the visual start of the line; if the window is scrolled horizontally (see Horizontal Scrolling), the column on which point will end is in addition to the number of columns by which the text is scrolled.The return value is the number of screen lines over which point was moved. The value may be less in absolute value than count if the beginning or end of the buffer was reached.
The window window is used for obtaining parameters such as the width, the horizontal scrolling, and the display table. But
vertical-motionalways operates on the current buffer, even if window currently displays some other buffer.The optional argument cur-col specifies the current column when the function is called. This is the window-relative horizontal coordinate of point, measured in units of font width of the frame's default face. Providing it speeds up the function, especially in very long lines, because it doesn't have to go back in the buffer in order to determine the current column. Note that cur-col is also counted from the visual start of the line.
This function returns the number of screen lines in the text from beg to end. The number of screen lines may be different from the number of actual lines, due to line continuation, the display table, etc. If beg and end are
nilor omitted, they default to the beginning and end of the accessible portion of the buffer.If the region ends with a newline, that is ignored unless the optional third argument count-final-newline is non-
nil.The optional fourth argument window specifies the window for obtaining parameters such as width, horizontal scrolling, and so on. The default is to use the selected window's parameters.
Like
vertical-motion,count-screen-linesalways uses the current buffer, regardless of which buffer is displayed in window. This makes possible to usecount-screen-linesin any buffer, whether or not it is currently displayed in some window.
This function moves point with respect to the text currently displayed in the selected window. It moves point to the beginning of the screen line count screen lines from the top of the window. If count is negative, that specifies a position −count lines from the bottom (or the last line of the buffer, if the buffer ends above the specified screen position).
If count is
nil, then point moves to the beginning of the line in the middle of the window. If the absolute value of count is greater than the size of the window, then point moves to the place that would appear on that screen line if the window were tall enough. This will probably cause the next redisplay to scroll to bring that location onto the screen.In an interactive call, count is the numeric prefix argument.
The value returned is the window line number point has moved to, with the top line in the window numbered 0.
This function is like
move-to-window-line, except that when the selected window is a part of a group of windows (see Window Group),move-to-window-group-linewill move to a position with respect to the entire group, not just the single window. This condition holds when the buffer local variablemove-to-window-group-line-functionis set to a function. In this case,move-to-window-group-linecalls the function with the argument count, then returns its result.
This function scans the current buffer, calculating screen positions. It scans the buffer forward from position from, assuming that is at screen coordinates frompos, to position to or coordinates topos, whichever comes first. It returns the ending buffer position and screen coordinates.
The coordinate arguments frompos and topos are cons cells of the form
(hpos.vpos).The argument width is the number of columns available to display text; this affects handling of continuation lines.
nilmeans the actual number of usable text columns in the window, which is equivalent to the value returned by(window-width window).The argument offsets is either
nilor a cons cell of the form(hscroll.tab-offset). Here hscroll is the number of columns not being displayed at the left margin; most callers get this by callingwindow-hscroll. Meanwhile, tab-offset is the offset between column numbers on the screen and column numbers in the buffer. This can be nonzero in a continuation line, when the previous screen lines' widths do not add up to a multiple oftab-width. It is always zero in a non-continuation line.The window window serves only to specify which display table to use.
compute-motionalways operates on the current buffer, regardless of what buffer is displayed in window.The return value is a list of five elements:
(pos hpos vpos prevhpos contin)Here pos is the buffer position where the scan stopped, vpos is the vertical screen position, and hpos is the horizontal screen position.
The result prevhpos is the horizontal position one character back from pos. The result contin is
tif the last line was continued after (or within) the previous character.For example, to find the buffer position of column col of screen line line of a certain window, pass the window's display start location as from and the window's upper-left coordinates as frompos. Pass the buffer's
(point-max)as to, to limit the scan to the end of the accessible portion of the buffer, and pass line and col as topos. Here's a function that does this:(defun coordinates-of-position (col line) (car (compute-motion (window-start) '(0 . 0) (point-max) (cons col line) (window-width) (cons (window-hscroll) 0) (selected-window))))When you use
compute-motionfor the minibuffer, you need to useminibuffer-prompt-widthto get the horizontal position of the beginning of the first screen line. See Minibuffer Contents.
Here are several functions concerned with balanced-parenthesis expressions (also called sexps in connection with moving across them in Emacs). The syntax table controls how these functions interpret various characters; see Syntax Tables. See Parsing Expressions, for lower-level primitives for scanning sexps or parts of sexps. For user-level commands, see Commands for Editing with Parentheses.
This function moves forward across arg (default 1) balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
This function moves backward across arg (default 1) balanced groups of parentheses. (Other syntactic entities such as words or paired string quotes are ignored.)
This function moves forward out of arg (default 1) levels of parentheses. A negative argument means move backward but still to a less deep spot. If escape-strings is non-
nil(as it is interactively), move out of enclosing strings as well. If no-syntax-crossing is non-nil(as it is interactively), prefer to break out of any enclosing string instead of moving to the start of a list broken across multiple strings. On error, location of point is unspecified.
This function is just like
up-list, but with a negated argument.
This function moves forward into arg (default 1) levels of parentheses. A negative argument means move backward but still go deeper in parentheses (−arg levels).
This function moves forward across arg (default 1) balanced expressions. Balanced expressions include both those delimited by parentheses and other kinds, such as words and string constants. See Parsing Expressions. For example,
---------- Buffer: foo ---------- (concat-!- "foo " (car x) y z) ---------- Buffer: foo ---------- (forward-sexp 3) => nil ---------- Buffer: foo ---------- (concat "foo " (car x) y-!- z) ---------- Buffer: foo ----------
This function moves backward across arg (default 1) balanced expressions.
This function moves back to the argth beginning of a defun. If arg is negative, this actually moves forward, but it still moves to the beginning of a defun, not to the end of one. arg defaults to 1.
This function moves forward to the argth end of a defun. If arg is negative, this actually moves backward, but it still moves to the end of a defun, not to the beginning of one. arg defaults to 1.
If non-
nil, this buffer-local variable holds a regular expression that specifies what text can appear before the open-parenthesis that starts a defun. That is to say, a defun begins on a line that starts with a match for this regular expression, followed by a character with open-parenthesis syntax.
If this variable's value is non-
nil, an open parenthesis in column 0 is considered to be the start of a defun. If it isnil, an open parenthesis in column 0 has no special meaning. The default ist.
If non-
nil, this variable holds a function for finding the beginning of a defun. The functionbeginning-of-defuncalls this function instead of using its normal method, passing it its optional argument. If the argument is non-nil, the function should move back by that many functions, likebeginning-of-defundoes.
If non-
nil, this variable holds a function for finding the end of a defun. The functionend-of-defuncalls this function instead of using its normal method.
The following two functions move point over a specified set of characters. For example, they are often used to skip whitespace. For related functions, see Motion and Syntax.
These functions convert the set string to multibyte if the buffer is multibyte, and they convert it to unibyte if the buffer is unibyte, as the search functions do (see Searching and Matching).
This function moves point in the current buffer forward, skipping over a given set of characters. It examines the character following point, then advances point if the character matches character-set. This continues until it reaches a character that does not match. The function returns the number of characters moved over.
The argument character-set is a string, like the inside of a `[...]' in a regular expression except that `]' does not terminate it, and `\' quotes `^', `-' or `\'. Thus,
"a-zA-Z"skips over all letters, stopping before the first nonletter, and"^a-zA-Z"skips nonletters stopping before the first letter. See See Regular Expressions. Character classes can also be used, e.g.,"[:alnum:]". See see Char Classes.If limit is supplied (it must be a number or a marker), it specifies the maximum position in the buffer that point can be skipped to. Point will stop at or before limit.
In the following example, point is initially located directly before the `T'. After the form is evaluated, point is located at the end of that line (between the `t' of `hat' and the newline). The function skips all letters and spaces, but not newlines.
---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (skip-chars-forward "a-zA-Z ") => 18 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function moves point backward, skipping characters that match character-set, until limit. It is just like
skip-chars-forwardexcept for the direction of motion.The return value indicates the distance traveled. It is an integer that is zero or less.
It is often useful to move point temporarily within a localized
portion of the program. This is called an excursion, and it is
done with the save-excursion special form. This construct
remembers the initial identity of the current buffer, and its value
of point, and restores them after the excursion
completes. It is the standard way to move point within one part of a
program and avoid affecting the rest of the program, and is used
thousands of times in the Lisp sources of Emacs.
If you only need to save and restore the identity of the current
buffer, use save-current-buffer or with-current-buffer
instead (see Current Buffer). If you need to save or restore
window configurations, see the forms described in Window Configurations and in Frame Configurations.
This special form saves the identity of the current buffer and the value of point in it, evaluates body, and finally restores the buffer and its saved value of point. Both saved values are restored even in case of an abnormal exit via
throwor error (see Nonlocal Exits).The value returned by
save-excursionis the result of the last form in body, ornilif no body forms were given.
Because save-excursion only saves point for the
buffer that was current at the start of the excursion, any changes
made to point in other buffers, during the excursion, will
remain in effect afterward. This frequently leads to unintended
consequences, so the byte compiler warns if you call set-buffer
during an excursion:
Warning: Use ‘with-current-buffer’ rather than
save-excursion+set-buffer
To avoid such problems, you should call save-excursion only
after setting the desired current buffer, as in the following example:
(defun append-string-to-buffer (string buffer)
"Append STRING to the end of BUFFER."
(with-current-buffer buffer
(save-excursion
(goto-char (point-max))
(insert string))))
Likewise, save-excursion does not restore window-buffer
correspondences altered by functions such as switch-to-buffer.
Warning: Ordinary insertion of text adjacent to the saved
point value relocates the saved value, just as it relocates all
markers. More precisely, the saved value is a marker with insertion
type nil. See Marker Insertion Types. Therefore, when the
saved point value is restored, it normally comes before the inserted
text.
This macro is like
save-excursion, but also saves and restores the mark location andmark-active. This macro does whatsave-excursiondid before Emacs 25.1.
Narrowing means limiting the text addressable by Emacs editing commands to a limited range of characters in a buffer. The text that remains addressable is called the accessible portion of the buffer.
Narrowing is specified with two buffer positions, which become the beginning and end of the accessible portion. For most editing commands and primitives, these positions replace the values of the beginning and end of the buffer. While narrowing is in effect, no text outside the accessible portion is displayed, and point cannot move outside the accessible portion. Note that narrowing does not alter actual buffer positions (see Point); it only determines which positions are considered the accessible portion of the buffer. Most functions refuse to operate on text that is outside the accessible portion.
Commands for saving buffers are unaffected by narrowing; they save the entire buffer regardless of any narrowing.
If you need to display in a single buffer several very different types of text, consider using an alternative facility described in Swapping Text.
This function sets the accessible portion of the current buffer to start at start and end at end. Both arguments should be character positions.
In an interactive call, start and end are set to the bounds of the current region (point and the mark, with the smallest first).
This function sets the accessible portion of the current buffer to include just the current page. An optional first argument move-count non-
nilmeans to move forward or backward by move-count pages and then narrow to one page. The variablepage-delimiterspecifies where pages start and end (see Standard Regexps).In an interactive call, move-count is set to the numeric prefix argument.
This function cancels any narrowing in the current buffer, so that the entire contents are accessible. This is called widening. It is equivalent to the following expression:
(narrow-to-region 1 (1+ (buffer-size)))
This function returns non-
nilif the buffer is narrowed, andnilotherwise.
This special form saves the current bounds of the accessible portion, evaluates the body forms, and finally restores the saved bounds, thus restoring the same state of narrowing (or absence thereof) formerly in effect. The state of narrowing is restored even in the event of an abnormal exit via
throwor error (see Nonlocal Exits). Therefore, this construct is a clean way to narrow a buffer temporarily.The value returned by
save-restrictionis that returned by the last form in body, ornilif no body forms were given.Caution: it is easy to make a mistake when using the
save-restrictionconstruct. Read the entire description here before you try it.If body changes the current buffer,
save-restrictionstill restores the restrictions on the original buffer (the buffer whose restrictions it saved from), but it does not restore the identity of the current buffer.
save-restrictiondoes not restore point; usesave-excursionfor that. If you use bothsave-restrictionandsave-excursiontogether,save-excursionshould come first (on the outside). Otherwise, the old point value would be restored with temporary narrowing still in effect. If the old point value were outside the limits of the temporary narrowing, this would fail to restore it accurately.Here is a simple example of correct use of
save-restriction:---------- Buffer: foo ---------- This is the contents of foo This is the contents of foo This is the contents of foo-!- ---------- Buffer: foo ---------- (save-excursion (save-restriction (goto-char 1) (forward-line 2) (narrow-to-region 1 (point)) (goto-char (point-min)) (replace-string "foo" "bar"))) ---------- Buffer: foo ---------- This is the contents of bar This is the contents of bar This is the contents of foo-!- ---------- Buffer: foo ----------
A marker is a Lisp object used to specify a position in a buffer relative to the surrounding text. A marker changes its offset from the beginning of the buffer automatically whenever text is inserted or deleted, so that it stays with the two characters on either side of it.
A marker specifies a buffer and a position in that buffer. A marker can be used to represent a position in functions that require one, just as an integer could be used. In that case, the marker's buffer is normally ignored. Of course, a marker used in this way usually points to a position in the buffer that the function operates on, but that is entirely the programmer's responsibility. See Positions, for a complete description of positions.
A marker has three attributes: the marker position, the marker buffer, and the insertion type. The marker position is an integer that is equivalent (at a given time) to the marker as a position in that buffer. But the marker's position value can change during the life of the marker, and often does. Insertion and deletion of text in the buffer relocate the marker. The idea is that a marker positioned between two characters remains between those two characters despite insertion and deletion elsewhere in the buffer. Relocation changes the integer equivalent of the marker.
Deleting text around a marker's position leaves the marker between the
characters immediately before and after the deleted text. Inserting
text at the position of a marker normally leaves the marker either in
front of or after the new text, depending on the marker's insertion
type (see Marker Insertion Types)—unless the insertion is done
with insert-before-markers (see Insertion).
Insertion and deletion in a buffer must check all the markers and relocate them if necessary. This slows processing in a buffer with a large number of markers. For this reason, it is a good idea to make a marker point nowhere if you are sure you don't need it any more. Markers that can no longer be accessed are eventually removed (see Garbage Collection).
Because it is common to perform arithmetic operations on a marker
position, most of these operations (including + and
-) accept markers as arguments. In such cases, the marker
stands for its current position.
Here are examples of creating markers, setting markers, and moving point to markers:
;; Make a new marker that initially does not point anywhere: (setq m1 (make-marker)) => #<marker in no buffer> ;; Setm1to point between the 99th and 100th characters ;; in the current buffer: (set-marker m1 100) => #<marker at 100 in markers.texi> ;; Now insert one character at the beginning of the buffer: (goto-char (point-min)) => 1 (insert "Q") => nil ;;m1is updated appropriately. m1 => #<marker at 101 in markers.texi> ;; Two markers that point to the same position ;; are noteq, but they areequal. (setq m2 (copy-marker m1)) => #<marker at 101 in markers.texi> (eq m1 m2) => nil (equal m1 m2) => t ;; When you are finished using a marker, make it point nowhere. (set-marker m1 nil) => #<marker in no buffer>
You can test an object to see whether it is a marker, or whether it is either an integer or a marker. The latter test is useful in connection with the arithmetic functions that work with both markers and integers.
This function returns
tif object is a marker,nilotherwise. Note that integers are not markers, even though many functions will accept either a marker or an integer.
This function returns
tif object is an integer or a marker,nilotherwise.
This function returns
tif object is a number (either integer or floating point) or a marker,nilotherwise.
When you create a new marker, you can make it point nowhere, or point to the present position of point, or to the beginning or end of the accessible portion of the buffer, or to the same place as another given marker.
The next four functions all return markers with insertion type
nil. See Marker Insertion Types.
This function returns a newly created marker that does not point anywhere.
(make-marker) => #<marker in no buffer>
This function returns a new marker that points to the present position of point in the current buffer. See Point. For an example, see
copy-marker, below.
This function returns a new marker that points to the beginning of the accessible portion of the buffer. This will be the beginning of the buffer unless narrowing is in effect. See Narrowing.
This function returns a new marker that points to the end of the accessible portion of the buffer. This will be the end of the buffer unless narrowing is in effect. See Narrowing.
Here are examples of this function and
point-min-marker, shown in a buffer containing a version of the source file for the text of this chapter.(point-min-marker) => #<marker at 1 in markers.texi> (point-max-marker) => #<marker at 24080 in markers.texi> (narrow-to-region 100 200) => nil (point-min-marker) => #<marker at 100 in markers.texi> (point-max-marker) => #<marker at 200 in markers.texi>
If passed a marker as its argument,
copy-markerreturns a new marker that points to the same place and the same buffer as does marker-or-integer. If passed an integer as its argument,copy-markerreturns a new marker that points to position marker-or-integer in the current buffer.The new marker's insertion type is specified by the argument insertion-type. See Marker Insertion Types.
(copy-marker 0) => #<marker at 1 in markers.texi> (copy-marker 90000) => #<marker at 24080 in markers.texi>An error is signaled if marker is neither a marker nor an integer.
Two distinct markers are considered equal (even though not
eq) to each other if they have the same position and buffer, or
if they both point nowhere.
(setq p (point-marker))
=> #<marker at 2139 in markers.texi>
(setq q (copy-marker p))
=> #<marker at 2139 in markers.texi>
(eq p q)
=> nil
(equal p q)
=> t
This section describes the functions for accessing the components of a marker object.
This function returns the position that marker points to, or
nilif it points nowhere.
This function returns the buffer that marker points into, or
nilif it points nowhere.(setq m (make-marker)) => #<marker in no buffer> (marker-position m) => nil (marker-buffer m) => nil (set-marker m 3770 (current-buffer)) => #<marker at 3770 in markers.texi> (marker-buffer m) => #<buffer markers.texi> (marker-position m) => 3770
When you insert text directly at the place where a marker points,
there are two possible ways to relocate that marker: it can point before
the inserted text, or point after it. You can specify which one a given
marker should do by setting its insertion type. Note that use of
insert-before-markers ignores markers' insertion types, always
relocating a marker to point after the inserted text.
This function sets the insertion type of marker marker to type. If type is
t, marker will advance when text is inserted at its position. If type isnil, marker does not advance when text is inserted there.
This function reports the current insertion type of marker.
Most functions that create markers, without an argument allowing to
specify the insertion type, create them with insertion type
nil. Also, the mark has, by default, insertion type
nil.
This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it—otherwise, confusing things may happen in other parts of Emacs.
This function moves marker to position in buffer. If buffer is not provided, it defaults to the current buffer.
If position is
nilor a marker that points nowhere, then marker is set to point nowhere.The value returned is marker.
(setq m (point-marker)) => #<marker at 4714 in markers.texi> (set-marker m 55) => #<marker at 55 in markers.texi> (setq b (get-buffer "foo")) => #<buffer foo> (set-marker m 0 b) => #<marker at 1 in foo>
Each buffer has a special marker, which is designated the mark. When a buffer is newly created, this marker exists but does not point anywhere; this means that the mark doesn't exist in that buffer yet. Subsequent commands can set the mark.
The mark specifies a position to bound a range of text for many
commands, such as kill-region and indent-rigidly. These
commands typically act on the text between point and the mark, which
is called the region. If you are writing a command that
operates on the region, don't examine the mark directly; instead, use
interactive with the `r' specification. This provides the
values of point and the mark as arguments to the command in an
interactive call, but permits other Lisp programs to specify arguments
explicitly. See Interactive Codes.
Some commands set the mark as a side-effect. Commands should do
this only if it has a potential use to the user, and never for their
own internal purposes. For example, the replace-regexp command
sets the mark to the value of point before doing any replacements,
because this enables the user to move back there conveniently after
the replace is finished.
Once the mark exists in a buffer, it normally never ceases to
exist. However, it may become inactive, if Transient Mark mode
is enabled. The buffer-local variable mark-active, if
non-nil, means that the mark is active. A command can call the
function deactivate-mark to deactivate the mark directly, or it
can request deactivation of the mark upon return to the editor command
loop by setting the variable deactivate-mark to a
non-nil value.
If Transient Mark mode is enabled, certain editing commands that normally apply to text near point, apply instead to the region when the mark is active. This is the main motivation for using Transient Mark mode. (Another is that this enables highlighting of the region when the mark is active. See Display.)
In addition to the mark, each buffer has a mark ring which is a
list of markers containing previous values of the mark. When editing
commands change the mark, they should normally save the old value of the
mark on the mark ring. The variable mark-ring-max specifies the
maximum number of entries in the mark ring; once the list becomes this
long, adding a new element deletes the last element.
There is also a separate global mark ring, but that is used only in a few particular user-level commands, and is not relevant to Lisp programming. So we do not describe it here.
This function returns the current buffer's mark position as an integer, or
nilif no mark has ever been set in this buffer.If Transient Mark mode is enabled, and
mark-even-if-inactiveisnil,marksignals an error if the mark is inactive. However, if force is non-nil, thenmarkdisregards inactivity of the mark, and returns the mark position (ornil) anyway.
This function returns the marker that represents the current buffer's mark. It is not a copy, it is the marker used internally. Therefore, changing this marker's position will directly affect the buffer's mark. Don't do that unless that is the effect you want.
(setq m (mark-marker)) => #<marker at 3420 in markers.texi> (set-marker m 100) => #<marker at 100 in markers.texi> (mark-marker) => #<marker at 100 in markers.texi>Like any marker, this marker can be set to point at any buffer you like. If you make it point at any buffer other than the one of which it is the mark, it will yield perfectly consistent, but rather odd, results. We recommend that you not do it!
This function sets the mark to position, and activates the mark. The old value of the mark is not pushed onto the mark ring.
Please note: Use this function only if you want the user to see that the mark has moved, and you want the previous mark position to be lost. Normally, when a new mark is set, the old one should go on the
mark-ring. For this reason, most applications should usepush-markandpop-mark, notset-mark.Novice Emacs Lisp programmers often try to use the mark for the wrong purposes. The mark saves a location for the user's convenience. An editing command should not alter the mark unless altering the mark is part of the user-level functionality of the command. (And, in that case, this effect should be documented.) To remember a location for internal use in the Lisp program, store it in a Lisp variable. For example:
(let ((beg (point))) (forward-line 1) (delete-region beg (point))).
This function sets the current buffer's mark to position, and pushes a copy of the previous mark onto
mark-ring. If position isnil, then the value of point is used.The function
push-marknormally does not activate the mark. To do that, specifytfor the argument activate.A `Mark set' message is displayed unless nomsg is non-
nil.
This function pops off the top element of
mark-ringand makes that mark become the buffer's actual mark. This does not move point in the buffer, and it does nothing ifmark-ringis empty. It deactivates the mark.
This variable, if non-
nil, enables Transient Mark mode. In Transient Mark mode, every buffer-modifying primitive setsdeactivate-mark. As a consequence, most commands that modify the buffer also deactivate the mark.When Transient Mark mode is enabled and the mark is active, many commands that normally apply to the text near point instead apply to the region. Such commands should use the function
use-region-pto test whether they should operate on the region. See The Region.Lisp programs can set
transient-mark-modeto non-nil, non-tvalues to enable Transient Mark mode temporarily. If the value islambda, Transient Mark mode is automatically turned off after any action, such as buffer modification, that would normally deactivate the mark. If the value is(only .oldval), thentransient-mark-modeis set to the value oldval after any subsequent command that moves point and is not shift-translated (see shift-translation), or after any other action that would normally deactivate the mark.
If this is non-
nil, Lisp programs and the Emacs user can use the mark even when it is inactive. This option affects the behavior of Transient Mark mode. When the option is non-nil, deactivation of the mark turns off region highlighting, but commands that use the mark behave as if the mark were still active.
If an editor command sets this variable non-
nil, then the editor command loop deactivates the mark after the command returns (if Transient Mark mode is enabled). All the primitives that change the buffer setdeactivate-mark, to deactivate the mark when the command is finished. Setting this variable makes it buffer-local.To write Lisp code that modifies the buffer without causing deactivation of the mark at the end of the command, bind
deactivate-marktonilaround the code that does the modification. For example:(let (deactivate-mark) (insert " "))
If Transient Mark mode is enabled or force is non-
nil, this function deactivates the mark and runs the normal hookdeactivate-mark-hook. Otherwise, it does nothing.
The mark is active when this variable is non-
nil. This variable is always buffer-local in each buffer. Do not use the value of this variable to decide whether a command that normally operates on text near point should operate on the region instead. Use the functionuse-region-pfor that (see The Region).
These normal hooks are run, respectively, when the mark becomes active and when it becomes inactive. The hook
activate-mark-hookis also run at the end of the command loop if the mark is active and it is possible that the region may have changed.
This function implements the shift-selection behavior of point-motion commands. See Shift Selection. It is called automatically by the Emacs command loop whenever a command with a `^' character in its
interactivespec is invoked, before the command itself is executed (see ^).If
shift-select-modeis non-niland the current command was invoked via shift translation (see shift-translation), this function sets the mark and temporarily activates the region, unless the region was already temporarily activated in this way. Otherwise, if the region has been activated temporarily, it deactivates the mark and restores the variabletransient-mark-modeto its earlier value.
The value of this buffer-local variable is the list of saved former marks of the current buffer, most recent first.
mark-ring => (#<marker at 11050 in markers.texi> #<marker at 10832 in markers.texi> ...)
The value of this variable is the maximum size of
mark-ring. If more marks than this are pushed onto themark-ring,push-markdiscards an old mark when it adds a new one.
When Delete Selection mode (see Delete Selection) is enabled, commands that operate on the
active region (a.k.a. “selection”) behave slightly differently.
This works by adding the function delete-selection-pre-hook to
the pre-command-hook (see Command Overview). That function
calls delete-selection-helper to delete the selection as
appropriate for the command. If you want to adapt a command to Delete
Selection mode, put the delete-selection property on the
function's symbol (see Symbol Plists); commands that don't have
this property on their symbol won't delete the selection. This
property can have one of several values to tailor the behavior to what
the command is supposed to do; see the doc strings of
delete-selection-pre-hook and delete-selection-helper
for the details.
The text between point and the mark is known as the region. Various functions operate on text delimited by point and the mark, but only those functions specifically related to the region itself are described here.
The next two functions signal an error if the mark does not point
anywhere. If Transient Mark mode is enabled and
mark-even-if-inactive is nil, they also signal an error
if the mark is inactive.
This function returns the position of the beginning of the region (as an integer). This is the position of either point or the mark, whichever is smaller.
This function returns the position of the end of the region (as an integer). This is the position of either point or the mark, whichever is larger.
Instead of using region-beginning and region-end, a
command designed to operate on a region should normally use
interactive with the `r' specification to find the
beginning and end of the region. This lets other Lisp programs
specify the bounds explicitly as arguments. See Interactive Codes.
This function returns
tif Transient Mark mode is enabled, the mark is active, and there is a valid region in the buffer. This function is intended to be used by commands that operate on the region, instead of on text near point, when the mark is active.A region is valid if it has a non-zero size, or if the user option
use-empty-active-regionis non-nil(by default, it isnil). The functionregion-active-pis similar touse-region-p, but considers all regions as valid. In most cases, you should not useregion-active-p, since if the region is empty it is often more appropriate to operate on point.
This chapter describes the functions that deal with the text in a buffer. Most examine, insert, or delete text in the current buffer, often operating at point or on text adjacent to point. Many are interactive. All the functions that change the text provide for undoing the changes (see Undo).
Many text-related functions operate on a region of text defined by two
buffer positions passed in arguments named start and end.
These arguments should be either markers (see Markers) or numeric
character positions (see Positions). The order of these arguments
does not matter; it is all right for start to be the end of the
region and end the beginning. For example, (delete-region 1
10) and (delete-region 10 1) are equivalent. An
args-out-of-range error is signaled if either start or
end is outside the accessible portion of the buffer. In an
interactive call, point and the mark are used for these arguments.
Throughout this chapter, “text” refers to the characters in the buffer, together with their properties (when relevant). Keep in mind that point is always between two characters, and the cursor appears on the character after point.
Many functions are provided to look at the characters around point.
Several simple functions are described here. See also looking-at
in Regexp Search.
In the following four functions, “beginning” or “end” of buffer refers to the beginning or end of the accessible portion.
This function returns the character in the current buffer at (i.e., immediately after) position position. If position is out of range for this purpose, either before the beginning of the buffer, or at or beyond the end, then the value is
nil. The default for position is point.In the following example, assume that the first character in the buffer is `@':
(string (char-after 1)) => "@"
This function returns the character in the current buffer immediately before position position. If position is out of range for this purpose, either at or before the beginning of the buffer, or beyond the end, then the value is
nil. The default for position is point.
This function returns the character following point in the current buffer. This is similar to
(char-after (point)). However, if point is at the end of the buffer, thenfollowing-charreturns 0.Remember that point is always between characters, and the cursor normally appears over the character following point. Therefore, the character returned by
following-charis the character the cursor is over.In this example, point is between the `a' and the `c'.
---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (string (preceding-char)) => "a" (string (following-char)) => "c"
This function returns the character preceding point in the current buffer. See above, under
following-char, for an example. If point is at the beginning of the buffer,preceding-charreturns 0.
This function returns
tif point is at the beginning of the buffer. If narrowing is in effect, this means the beginning of the accessible portion of the text. See alsopoint-minin Point.
This function returns
tif point is at the end of the buffer. If narrowing is in effect, this means the end of accessible portion of the text. See alsopoint-maxin See Point.
This function returns
tif point is at the beginning of a line. See Text Lines. The beginning of the buffer (or of its accessible portion) always counts as the beginning of a line.
This function returns
tif point is at the end of a line. The end of the buffer (or of its accessible portion) is always considered the end of a line.
This section describes functions that allow a Lisp program to convert any portion of the text in the buffer into a string.
This function returns a string containing a copy of the text of the region defined by positions start and end in the current buffer. If the arguments are not positions in the accessible portion of the buffer,
buffer-substringsignals anargs-out-of-rangeerror.Here's an example which assumes Font-Lock mode is not enabled:
---------- Buffer: foo ---------- This is the contents of buffer foo ---------- Buffer: foo ---------- (buffer-substring 1 10) => "This is t" (buffer-substring (point-max) 10) => "he contents of buffer foo\n"If the text being copied has any text properties, these are copied into the string along with the characters they belong to. See Text Properties. However, overlays (see Overlays) in the buffer and their properties are ignored, not copied.
For example, if Font-Lock mode is enabled, you might get results like these:
(buffer-substring 1 10) => #("This is t" 0 1 (fontified t) 1 9 (fontified t))
This is like
buffer-substring, except that it does not copy text properties, just the characters themselves. See Text Properties.
This function returns the contents of the entire accessible portion of the current buffer, as a string.
If you need to make sure the resulting string, when copied to a
different location, will not change its visual appearance due to
reordering of bidirectional text, use the
buffer-substring-with-bidi-context function
(see buffer-substring-with-bidi-context).
This function filters the buffer text between start and end using a function specified by the variable
filter-buffer-substring-function, and returns the result.The default filter function consults the obsolete wrapper hook
filter-buffer-substring-functions, and the obsolete variablebuffer-substring-filters. If both of these arenil, it returns the unaltered text from the buffer, i.e., whatbuffer-substringwould return.If delete is non-
nil, the function deletes the text between start and end after copying it, likedelete-and-extract-region.Lisp code should use this function instead of
buffer-substring,buffer-substring-no-properties, ordelete-and-extract-regionwhen copying into user-accessible data structures such as the kill-ring, X clipboard, and registers. Major and minor modes can modifyfilter-buffer-substring-functionto alter such text as it is copied out of the buffer.
The value of this variable is a function that
filter-buffer-substringwill call to do the actual work. The function receives three arguments, the same as those offilter-buffer-substring, which it should treat as per the documentation of that function. It should return the filtered text (and optionally delete the source text).
The following two variables are obsoleted by
filter-buffer-substring-function, but are still supported for
backward compatibility.
This obsolete variable is a wrapper hook, whose members should be functions that accept four arguments: fun, start, end, and delete. fun is a function that takes three arguments (start, end, and delete), and returns a string. In both cases, the start, end, and delete arguments are the same as those of
filter-buffer-substring.The first hook function is passed a fun that is equivalent to the default operation of
filter-buffer-substring, i.e., it returns the buffer-substring between start and end (processed by anybuffer-substring-filters) and optionally deletes the original text from the buffer. In most cases, the hook function will call fun once, and then do its own processing of the result. The next hook function receives a fun equivalent to this, and so on. The actual return value is the result of all the hook functions acting in sequence.
The value of this obsolete variable should be a list of functions that accept a single string argument and return another string. The default
filter-buffer-substringfunction passes the buffer substring to the first function in this list, and the return value of each function is passed to the next function. The return value of the last function is passed tofilter-buffer-substring-functions.
This function returns the symbol (or word) at or near point, as a string. The return value includes no text properties.
If the optional argument really-word is non-
nil, it finds a word; otherwise, it finds a symbol (which includes both word characters and symbol constituent characters).If the optional argument strict is non-
nil, then point must be in or next to the symbol or word—if no symbol or word is there, the function returnsnil. Otherwise, a nearby symbol or word on the same line is acceptable.
Return the thing around or next to point, as a string.
The argument thing is a symbol which specifies a kind of syntactic entity. Possibilities include
symbol,list,sexp,defun,filename,url,word,sentence,whitespace,line,page, and others.When the optional argument no-properties is non-
nil, this function strips text properties from the return value.---------- Buffer: foo ---------- Gentlemen may cry ``Pea-!-ce! Peace!,'' but there is no peace. ---------- Buffer: foo ---------- (thing-at-point 'word) => "Peace" (thing-at-point 'line) => "Gentlemen may cry ``Peace! Peace!,''\n" (thing-at-point 'whitespace) => nil
This function lets you compare portions of the text in a buffer, without copying them into strings first.
This function lets you compare two substrings of the same buffer or two different buffers. The first three arguments specify one substring, giving a buffer (or a buffer name) and two positions within the buffer. The last three arguments specify the other substring in the same way. You can use
nilfor buffer1, buffer2, or both to stand for the current buffer.The value is negative if the first substring is less, positive if the first is greater, and zero if they are equal. The absolute value of the result is one plus the index of the first differing characters within the substrings.
This function ignores case when comparing characters if
case-fold-searchis non-nil. It always ignores text properties.Suppose you have the text `foobarbar haha!rara!' in the current buffer; then in this example the two substrings are `rbar ' and `rara!'. The value is 2 because the first substring is greater at the second character.
(compare-buffer-substrings nil 6 11 nil 16 21) => 2
Insertion means adding new text to a buffer. The inserted text goes at point—between the character before point and the character after point. Some insertion functions leave point before the inserted text, while other functions leave it after. We call the former insertion after point and the latter insertion before point.
Insertion moves markers located at positions after the insertion
point, so that they stay with the surrounding text (see Markers).
When a marker points at the place of insertion, insertion may or may
not relocate the marker, depending on the marker's insertion type
(see Marker Insertion Types). Certain special functions such as
insert-before-markers relocate all such markers to point after
the inserted text, regardless of the markers' insertion type.
Insertion functions signal an error if the current buffer is read-only (see Read Only Buffers) or if they insert within read-only text (see Special Properties).
These functions copy text characters from strings and buffers along with their properties. The inserted characters have exactly the same properties as the characters they were copied from. By contrast, characters specified as separate arguments, not part of a string or buffer, inherit their text properties from the neighboring text.
The insertion functions convert text from unibyte to multibyte in order to insert in a multibyte buffer, and vice versa—if the text comes from a string or from a buffer. However, they do not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See Converting Representations.
This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. In other words, it inserts the text before point. An error is signaled unless all args are either strings or characters. The value is
nil.
This function inserts the strings and/or characters args into the current buffer, at point, moving point forward. An error is signaled unless all args are either strings or characters. The value is
nil.This function is unlike the other insertion functions in that it relocates markers initially pointing at the insertion point, to point after the inserted text. If an overlay begins at the insertion point, the inserted text falls outside the overlay; if a nonempty overlay ends at the insertion point, the inserted text falls inside that overlay.
This command inserts count instances of character into the current buffer before point. The argument count must be an integer, and character must be a character.
If called interactively, this command prompts for character using its Unicode name or its code point. See Inserting Text.
This function does not convert unibyte character codes 128 through 255 to multibyte characters, not even if the current buffer is a multibyte buffer. See Converting Representations.
If inherit is non-
nil, the inserted characters inherit sticky text properties from the two characters before and after the insertion point. See Sticky Properties.
This function inserts a portion of buffer from-buffer-or-name into the current buffer before point. The text inserted is the region between start (inclusive) and end (exclusive). (These arguments default to the beginning and end of the accessible portion of that buffer.) This function returns
nil.In this example, the form is executed with buffer `bar' as the current buffer. We assume that buffer `bar' is initially empty.
---------- Buffer: foo ---------- We hold these truths to be self-evident, that all ---------- Buffer: foo ---------- (insert-buffer-substring "foo" 1 20) => nil ---------- Buffer: bar ---------- We hold these truth-!- ---------- Buffer: bar ----------
This is like
insert-buffer-substringexcept that it does not copy any text properties.
See Sticky Properties, for other insertion functions that inherit text properties from the nearby text in addition to inserting it. Whitespace inserted by indentation functions also inherits text properties.
This section describes higher-level commands for inserting text, commands intended primarily for the user but useful also in Lisp programs.
This command inserts the entire accessible contents of from-buffer-or-name (which must exist) into the current buffer after point. It leaves the mark after the inserted text. The value is
nil.
This command inserts the last character typed; it does so count times, before point, and returns
nil. Most printing characters are bound to this command. In routine use,self-insert-commandis the most frequently called function in Emacs, but programs rarely use it except to install it on a keymap.In an interactive call, count is the numeric prefix argument.
Self-insertion translates the input character through
translation-table-for-input. See Translation of Characters.This command calls
auto-fill-functionwhenever that is non-niland the character inserted is in the tableauto-fill-chars(see Auto Filling).This command performs abbrev expansion if Abbrev mode is enabled and the inserted character does not have word-constituent syntax. (See Abbrevs, and Syntax Class Table.) It is also responsible for calling
blink-paren-functionwhen the inserted character has close parenthesis syntax (see Blinking).The final thing this command does is to run the hook
post-self-insert-hook. You could use this to automatically reindent text as it is typed, for example.Do not try substituting your own definition of
self-insert-commandfor the standard one. The editor command loop handles this function specially.
This command inserts newlines into the current buffer before point. If number-of-newlines is supplied, that many newline characters are inserted.
This function calls
auto-fill-functionif the current column number is greater than the value offill-columnand number-of-newlines isnil. Typically whatauto-fill-functiondoes is insert a newline; thus, the overall result in this case is to insert two newlines at different places: one at point, and another earlier in the line.newlinedoes not auto-fill if number-of-newlines is non-nil.This command indents to the left margin if that is not zero. See Margins.
The value returned is
nil. In an interactive call, count is the numeric prefix argument.
This variable controls whether overwrite mode is in effect. The value should be
overwrite-mode-textual,overwrite-mode-binary, ornil.overwrite-mode-textualspecifies textual overwrite mode (treats newlines and tabs specially), andoverwrite-mode-binaryspecifies binary overwrite mode (treats newlines and tabs like any other characters).
Deletion means removing part of the text in a buffer, without saving it in the kill ring (see The Kill Ring). Deleted text can't be yanked, but can be reinserted using the undo mechanism (see Undo). Some deletion functions do save text in the kill ring in some special cases.
All of the deletion functions operate on the current buffer.
This function deletes the entire text of the current buffer (not just the accessible portion), leaving it empty. If the buffer is read-only, it signals a
buffer-read-onlyerror; if some of the text in it is read-only, it signals atext-read-onlyerror. Otherwise, it deletes the text without asking for any confirmation. It returnsnil.Normally, deleting a large amount of text from a buffer inhibits further auto-saving of that buffer because it has shrunk. However,
erase-bufferdoes not do this, the idea being that the future text is not really related to the former text, and its size should not be compared with that of the former text.
This command deletes the text between positions start and end in the current buffer, and returns
nil. If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.
This function deletes the text between positions start and end in the current buffer, and returns a string containing the text just deleted.
If point was inside the deleted region, its value afterward is start. Otherwise, point relocates with the surrounding text, as markers do.
This command deletes count characters directly after point, or before point if count is negative. If killp is non-
nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This command deletes count characters directly before point, or after point if count is negative. If killp is non-
nil, then it saves the deleted characters in the kill ring.In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This command deletes count characters backward, changing tabs into spaces. When the next character to be deleted is a tab, it is first replaced with the proper number of spaces to preserve alignment and then one of those spaces is deleted instead of the tab. If killp is non-
nil, then the command saves the deleted characters in the kill ring.Conversion of tabs to spaces happens only if count is positive. If it is negative, exactly −count characters after point are deleted.
In an interactive call, count is the numeric prefix argument, and killp is the unprocessed prefix argument. Therefore, if a prefix argument is supplied, the text is saved in the kill ring. If no prefix argument is supplied, then one character is deleted, but not saved in the kill ring.
The value returned is always
nil.
This option specifies how
backward-delete-char-untabifyshould deal with whitespace. Possible values includeuntabify, the default, meaning convert a tab to many spaces and delete one;hungry, meaning delete all tabs and spaces before point with one command;allmeaning delete all tabs, spaces and newlines before point, andnil, meaning do nothing special for whitespace characters.
This section describes higher-level commands for deleting text, commands intended primarily for the user but useful also in Lisp programs.
This function deletes all spaces and tabs around point. It returns
nil.If backward-only is non-
nil, the function deletes spaces and tabs before point, but not after point.In the following examples, we call
delete-horizontal-spacefour times, once on each line, with point between the second and third characters on the line each time.---------- Buffer: foo ---------- I -!-thought I -!- thought We-!- thought Yo-!-u thought ---------- Buffer: foo ---------- (delete-horizontal-space) ; Four times. => nil ---------- Buffer: foo ---------- Ithought Ithought Wethought You thought ---------- Buffer: foo ----------
This function joins the line point is on to the previous line, deleting any whitespace at the join and in some cases replacing it with one space. If join-following-p is non-
nil,delete-indentationjoins this line to the following line instead. The function returnsnil.If there is a fill prefix, and the second of the lines being joined starts with the prefix, then
delete-indentationdeletes the fill prefix before joining the lines. See Margins.In the example below, point is located on the line starting `events', and it makes no difference if there are trailing spaces in the preceding line.
---------- Buffer: foo ---------- When in the course of human -!- events, it becomes necessary ---------- Buffer: foo ---------- (delete-indentation) => nil ---------- Buffer: foo ---------- When in the course of human-!- events, it becomes necessary ---------- Buffer: foo ----------After the lines are joined, the function
fixup-whitespaceis responsible for deciding whether to leave a space at the junction.
This function replaces all the horizontal whitespace surrounding point with either one space or no space, according to the context. It returns
nil.At the beginning or end of a line, the appropriate amount of space is none. Before a character with close parenthesis syntax, or after a character with open parenthesis or expression-prefix syntax, no space is also appropriate. Otherwise, one space is appropriate. See Syntax Class Table.
In the example below,
fixup-whitespaceis called the first time with point before the word `spaces' in the first line. For the second invocation, point is directly after the `('.---------- Buffer: foo ---------- This has too many -!-spaces This has too many spaces at the start of (-!- this list) ---------- Buffer: foo ---------- (fixup-whitespace) => nil (fixup-whitespace) => nil ---------- Buffer: foo ---------- This has too many spaces This has too many spaces at the start of (this list) ---------- Buffer: foo ----------
This command replaces any spaces and tabs around point with a single space, or n spaces if n is specified. It returns
nil.
This function deletes blank lines surrounding point. If point is on a blank line with one or more blank lines before or after it, then all but one of them are deleted. If point is on an isolated blank line, then it is deleted. If point is on a nonblank line, the command deletes all blank lines immediately following it.
A blank line is defined as a line containing only tabs and spaces.
delete-blank-linesreturnsnil.
Delete trailing whitespace in the region defined by start and end.
This command deletes whitespace characters after the last non-whitespace character in each line in the region.
If this command acts on the entire buffer (i.e., if called interactively with the mark inactive, or called from Lisp with end
nil), it also deletes all trailing lines at the end of the buffer if the variabledelete-trailing-linesis non-nil.
Kill functions delete text like the deletion functions, but save it so that the user can reinsert it by yanking. Most of these functions have `kill-' in their name. By contrast, the functions whose names start with `delete-' normally do not save text for yanking (though they can still be undone); these are deletion functions.
Most of the kill commands are primarily for interactive use, and are not described here. What we do describe are the functions provided for use in writing such commands. You can use these functions to write commands for killing text. When you need to delete text for internal purposes within a Lisp function, you should normally use deletion functions, so as not to disturb the kill ring contents. See Deletion.
Killed text is saved for later yanking in the kill ring. This
is a list that holds a number of recent kills, not just the last text
kill. We call this a “ring” because yanking treats it as having
elements in a cyclic order. The list is kept in the variable
kill-ring, and can be operated on with the usual functions for
lists; there are also specialized functions, described in this section,
that treat it as a ring.
Some people think this use of the word “kill” is unfortunate, since it refers to operations that specifically do not destroy the entities killed. This is in sharp contrast to ordinary life, in which death is permanent and killed entities do not come back to life. Therefore, other metaphors have been proposed. For example, the term “cut ring” makes sense to people who, in pre-computer days, used scissors and paste to cut up and rearrange manuscripts. However, it would be difficult to change the terminology now.
The kill ring records killed text as strings in a list, most recent first. A short kill ring, for example, might look like this:
("some text" "a different piece of text" "even older text")
When the list reaches kill-ring-max entries in length, adding a
new entry automatically deletes the last entry.
When kill commands are interwoven with other commands, each kill command makes a new entry in the kill ring. Multiple kill commands in succession build up a single kill ring entry, which would be yanked as a unit; the second and subsequent consecutive kill commands add text to the entry made by the first one.
For yanking, one entry in the kill ring is designated the front of the ring. Some yank commands rotate the ring by designating a different element as the front. But this virtual rotation doesn't change the list itself—the most recent entry always comes first in the list.
kill-region is the usual subroutine for killing text. Any
command that calls this function is a kill command (and should
probably have `kill' in its name). kill-region puts the
newly killed text in a new element at the beginning of the kill ring or
adds it to the most recent element. It determines automatically (using
last-command) whether the previous command was a kill command,
and if so appends the killed text to the most recent entry.
The commands described below can filter the killed text before they
save it in the kill ring. They call filter-buffer-substring
(see Buffer Contents) to perform the filtering. By default,
there's no filtering, but major and minor modes and hook functions can
set up filtering, so that text saved in the kill ring is different
from what was in the buffer.
This function kills the stretch of text between start and end; but if the optional argument region is non-
nil, it ignores start and end, and kills the text in the current region instead. The text is deleted but saved in the kill ring, along with its text properties. The value is alwaysnil.In an interactive call, start and end are point and the mark, and region is always non-
nil, so the command always kills the text in the current region.If the buffer or text is read-only,
kill-regionmodifies the kill ring just the same, then signals an error without modifying the buffer. This is convenient because it lets the user use a series of kill commands to copy text from a read-only buffer into the kill ring.
If this option is non-
nil,kill-regiondoes not signal an error if the buffer or text is read-only. Instead, it simply returns, updating the kill ring but not changing the buffer.
This function saves the stretch of text between start and end on the kill ring (including text properties), but does not delete the text from the buffer. However, if the optional argument region is non-
nil, the function ignores start and end, and saves the current region instead. It always returnsnil.In an interactive call, start and end are point and the mark, and region is always non-
nil, so the command always saves the text in the current region.The command does not set
this-commandtokill-region, so a subsequent kill command does not append to the same kill ring entry.
Yanking means inserting text from the kill ring, but it does not
insert the text blindly. The yank command, and related
commands, use insert-for-yank to perform special processing on
the text before it is inserted.
This function works like
insert, except that it processes the text in string according to theyank-handlertext property, as well as the variablesyank-handled-propertiesandyank-excluded-properties(see below), before inserting the result into the current buffer.
This function resembles
insert-buffer-substring, except that it processes the text according toyank-handled-propertiesandyank-excluded-properties. (It does not handle theyank-handlerproperty, which does not normally occur in buffer text anyway.)
If you put a yank-handler text property on all or part of a
string, that alters how insert-for-yank inserts the string. If
different parts of the string have different yank-handler
values (comparison being done with eq), each substring is
handled separately. The property value must be a list of one to four
elements, with the following format (where elements after the first
may be omitted):
(function param noexclude undo)
Here is what the elements do:
nil, it is called instead of
insert to insert the string, with one argument—the string to
insert.
nil, it replaces string
(or the substring of string being processed) as the object
passed to function (or insert). For example, if
function is yank-rectangle, param should be a list
of strings to insert as a rectangle.
nil, that disables the
normal action of yank-handled-properties and
yank-excluded-properties on the inserted string.
nil, it is a function that will be
called by yank-pop to undo the insertion of the current object.
It is called with two arguments, the start and end of the current
region. function can set yank-undo-function to override
the undo value.
This variable specifies special text property handling conditions for yanked text. It takes effect after the text has been inserted (either normally, or via the
yank-handlerproperty), and prior toyank-excluded-propertiestaking effect.The value should be an alist of elements
(prop.fun). Each alist element is handled in order. The inserted text is scanned for stretches of text having text propertieseqto prop; for each such stretch, fun is called with three arguments: the value of the property, and the start and end positions of the text.
The value of this variable is the list of properties to remove from inserted text. Its default value contains properties that might lead to annoying results, such as causing the text to respond to the mouse or specifying key bindings. It takes effect after
yank-handled-properties.
This section describes higher-level commands for yanking, which are
intended primarily for the user but useful also in Lisp programs.
Both yank and yank-pop honor the
yank-excluded-properties variable and yank-handler text
property (see Yanking).
This command inserts before point the text at the front of the kill ring. It sets the mark at the beginning of that text, using
push-mark(see The Mark), and puts point at the end.If arg is a non-
nillist (which occurs interactively when the user types C-u with no digits), thenyankinserts the text as described above, but puts point before the yanked text and sets the mark after it.If arg is a number, then
yankinserts the argth most recently killed text—the argth element of the kill ring list, counted cyclically from the front, which is considered the first element for this purpose.
yankdoes not alter the contents of the kill ring, unless it used text provided by another program, in which case it pushes that text onto the kill ring. However if arg is an integer different from one, it rotates the kill ring to place the yanked string at the front.
yankreturnsnil.
This command replaces the just-yanked entry from the kill ring with a different entry from the kill ring.
This is allowed only immediately after a
yankor anotheryank-pop. At such a time, the region contains text that was just inserted by yanking.yank-popdeletes that text and inserts in its place a different piece of killed text. It does not add the deleted text to the kill ring, since it is already in the kill ring somewhere. It does however rotate the kill ring to place the newly yanked string at the front.If arg is
nil, then the replacement text is the previous element of the kill ring. If arg is numeric, the replacement is the argth previous kill. If arg is negative, a more recent kill is the replacement.The sequence of kills in the kill ring wraps around, so that after the oldest one comes the newest one, and before the newest one goes the oldest.
The return value is always
nil.
If this variable is non-
nil, the functionyank-popuses its value instead ofdelete-regionto delete the text inserted by the previousyankoryank-popcommand. The value must be a function of two arguments, the start and end of the current region.The function
insert-for-yankautomatically sets this variable according to the undo element of theyank-handlertext property, if there is one.
These functions and variables provide access to the kill ring at a lower level, but are still convenient for use in Lisp programs, because they take care of interaction with window system selections (see Window System Selections).
The function
current-killrotates the yanking pointer, which designates the front of the kill ring, by n places (from newer kills to older ones), and returns the text at that place in the ring.If the optional second argument do-not-move is non-
nil, thencurrent-killdoesn't alter the yanking pointer; it just returns the nth kill, counting from the current yanking pointer.If n is zero, indicating a request for the latest kill,
current-killcalls the value ofinterprogram-paste-function(documented below) before consulting the kill ring. If that value is a function and calling it returns a string or a list of several string,current-killpushes the strings onto the kill ring and returns the first string. It also sets the yanking pointer to point to the kill-ring entry of the first string returned byinterprogram-paste-function, regardless of the value of do-not-move. Otherwise,current-killdoes not treat a zero value for n specially: it returns the entry pointed at by the yanking pointer and does not move the yanking pointer.
This function pushes the text string onto the kill ring and makes the yanking pointer point to it. It discards the oldest entry if appropriate. It also invokes the value of
interprogram-cut-function(see below).If replace is non-
nil, thenkill-newreplaces the first element of the kill ring with string, rather than pushing string onto the kill ring.
This function appends the text string to the first entry in the kill ring and makes the yanking pointer point to the combined entry. Normally string goes at the end of the entry, but if before-p is non-
nil, it goes at the beginning. This function also invokes the value ofinterprogram-cut-function(see below).
This variable provides a way of transferring killed text from other programs, when you are using a window system. Its value should be
nilor a function of no arguments.If the value is a function,
current-killcalls it to get the most recent kill. If the function returns a non-nilvalue, then that value is used as the most recent kill. If it returnsnil, then the front of the kill ring is used.To facilitate support for window systems that support multiple selections, this function may also return a list of strings. In that case, the first string is used as the most recent kill, and all the other strings are pushed onto the kill ring, for easy access by
yank-pop.The normal use of this function is to get the window system's clipboard as the most recent kill, even if the selection belongs to another application. See Window System Selections. However, if the clipboard contents come from the current Emacs session, this function should return
nil.
This variable provides a way of communicating killed text to other programs, when you are using a window system. Its value should be
nilor a function of one required argument.If the value is a function,
kill-newandkill-appendcall it with the new first element of the kill ring as the argument.The normal use of this function is to put newly killed text in the window system's clipboard. See Window System Selections.
The variable kill-ring holds the kill ring contents, in the
form of a list of strings. The most recent kill is always at the front
of the list.
The kill-ring-yank-pointer variable points to a link in the
kill ring list, whose car is the text to yank next. We say it
identifies the front of the ring. Moving
kill-ring-yank-pointer to a different link is called
rotating the kill ring. We call the kill ring a “ring” because
the functions that move the yank pointer wrap around from the end of the
list to the beginning, or vice-versa. Rotation of the kill ring is
virtual; it does not change the value of kill-ring.
Both kill-ring and kill-ring-yank-pointer are Lisp
variables whose values are normally lists. The word “pointer” in the
name of the kill-ring-yank-pointer indicates that the variable's
purpose is to identify one element of the list for use by the next yank
command.
The value of kill-ring-yank-pointer is always eq to one
of the links in the kill ring list. The element it identifies is the
car of that link. Kill commands, which change the kill ring, also
set this variable to the value of kill-ring. The effect is to
rotate the ring so that the newly killed text is at the front.
Here is a diagram that shows the variable kill-ring-yank-pointer
pointing to the second entry in the kill ring ("some text" "a
different piece of text" "yet older text").
kill-ring ---- kill-ring-yank-pointer
| |
| v
| --- --- --- --- --- ---
--> | | |------> | | |--> | | |--> nil
--- --- --- --- --- ---
| | |
| | |
| | -->"yet older text"
| |
| --> "a different piece of text"
|
--> "some text"
This state of affairs might occur after C-y (yank)
immediately followed by M-y (yank-pop).
This variable holds the list of killed text sequences, most recently killed first.
This variable's value indicates which element of the kill ring is at the front of the ring for yanking. More precisely, the value is a tail of the value of
kill-ring, and its car is the kill string that C-y should yank.
The value of this variable is the maximum length to which the kill ring can grow, before elements are thrown away at the end. The default value for
kill-ring-maxis 60.
Most buffers have an undo list, which records all changes made
to the buffer's text so that they can be undone. (The buffers that
don't have one are usually special-purpose buffers for which Emacs
assumes that undoing is not useful. In particular, any buffer whose
name begins with a space has its undo recording off by default;
see Buffer Names.) All the primitives that modify the
text in the buffer automatically add elements to the front of the undo
list, which is in the variable buffer-undo-list.
This buffer-local variable's value is the undo list of the current buffer. A value of
tdisables the recording of undo information.
Here are the kinds of elements an undo list can have:
(beg . end)
(text . position)
(abs position). If position is
positive, point was at the beginning of the deleted text, otherwise it
was at the end. Zero or more (marker . adjustment)
elements follow immediately after this element.
(t . time-flag)
(sec-high sec-low microsec
picosec) represents the visited file's modification time as of
when it was previously visited or saved, using the same format as
current-time; see Time of Day.
A time-flag of 0 means the buffer does not correspond to any file;
−1 means the visited file previously did not exist.
primitive-undo uses these
values to determine whether to mark the buffer as unmodified once again;
it does so only if the file's status matches that of time-flag.
(nil property value beg . end)
(put-text-property beg end property value)
(marker . adjustment)
(apply funname . args)
(apply delta beg end funname . args)
This kind of element enables undo limited to a region to determine
whether the element pertains to that region.
nilThis function places a boundary element in the undo list. The undo command stops at such a boundary, and successive undo commands undo to earlier and earlier boundaries. This function returns
nil.Calling this function explicitly is useful for splitting the effects of a command into more than one unit. For example,
query-replacecallsundo-boundaryafter each replacement, so that the user can undo individual replacements one by one.Mostly, however, this function is called automatically at an appropriate time.
The editor command loop automatically calls
undo-boundaryjust before executing each key sequence, so that each undo normally undoes the effects of one command. A few exceptional commands are amalgamating: these commands generally cause small changes to buffers, so with these a boundary is inserted only every 20th command, allowing to undo them as a group. By default, commandsself-insert-command, which produces self-inserting input characters (see Commands for Insertion), anddelete-charwhich deletes characters (see Deletion) are amalgamating. Where a command affects the contents of several buffers, as may happen, for example, when a function on thepost-command-hookaffects a buffer other than thecurrent-buffer, thenundo-boundarywill be called in each of the affected buffers.
Some buffers, such as process buffers, can change even when no commands are executing. In these cases,
undo-boundaryis normally called periodically by the timer in this variable. Setting this variable to non-nilprevents this behavior.
This variable is normally
nil, but the undo commands bind it tot. This is so that various kinds of change hooks can tell when they're being called for the sake of undoing.
This is the basic function for undoing elements of an undo list. It undoes the first count elements of list, returning the rest of list.
primitive-undoadds elements to the buffer's undo list when it changes the buffer. Undo commands avoid confusion by saving the undo list value at the beginning of a sequence of undo operations. Then the undo operations use and update the saved value. The new elements added by undoing are not part of this saved value, so they don't interfere with continuing to undo.This function does not bind
undo-in-progress.
This section describes how to enable and disable undo information for a given buffer. It also explains how the undo list is truncated automatically so it doesn't get too big.
Recording of undo information in a newly created buffer is normally
enabled to start with; but if the buffer name starts with a space, the
undo recording is initially disabled. You can explicitly enable or
disable undo recording with the following two functions, or by setting
buffer-undo-list yourself.
This command enables recording undo information for buffer buffer-or-name, so that subsequent changes can be undone. If no argument is supplied, then the current buffer is used. This function does nothing if undo recording is already enabled in the buffer. It returns
nil.In an interactive call, buffer-or-name is the current buffer. You cannot specify any other buffer.
This function discards the undo list of buffer-or-name, and disables further recording of undo information. As a result, it is no longer possible to undo either previous changes or any subsequent changes. If the undo list of buffer-or-name is already disabled, this function has no effect.
In an interactive call, BUFFER-OR-NAME is the current buffer. You cannot specify any other buffer. This function returns
nil.
As editing continues, undo lists get longer and longer. To prevent
them from using up all available memory space, garbage collection trims
them back to size limits you can set. (For this purpose, the size
of an undo list measures the cons cells that make up the list, plus the
strings of deleted text.) Three variables control the range of acceptable
sizes: undo-limit, undo-strong-limit and
undo-outer-limit. In these variables, size is counted as the
number of bytes occupied, which includes both saved text and other
data.
This is the soft limit for the acceptable size of an undo list. The change group at which this size is exceeded is the last one kept.
This is the upper limit for the acceptable size of an undo list. The change group at which this size is exceeded is discarded itself (along with all older change groups). There is one exception: the very latest change group is only discarded if it exceeds
undo-outer-limit.
If at garbage collection time the undo info for the current command exceeds this limit, Emacs discards the info and displays a warning. This is a last ditch limit to prevent memory overflow.
If this variable is non-
nil, when the undo info exceedsundo-outer-limit, Emacs asks in the echo area whether to discard the info. The default value isnil, which means to discard it automatically.This option is mainly intended for debugging. Garbage collection is inhibited while the question is asked, which means that Emacs might leak memory if the user waits too long before answering the question.
Filling means adjusting the lengths of lines (by moving the line
breaks) so that they are nearly (but no greater than) a specified
maximum width. Additionally, lines can be justified, which means
inserting spaces to make the left and/or right margins line up
precisely. The width is controlled by the variable fill-column.
For ease of reading, lines should be no longer than 70 or so columns.
You can use Auto Fill mode (see Auto Filling) to fill text automatically as you insert it, but changes to existing text may leave it improperly filled. Then you must fill the text explicitly.
Most of the commands in this section return values that are not
meaningful. All the functions that do filling take note of the current
left margin, current right margin, and current justification style
(see Margins). If the current justification style is
none, the filling functions don't actually do anything.
Several of the filling functions have an argument justify.
If it is non-nil, that requests some kind of justification. It
can be left, right, full, or center, to
request a specific style of justification. If it is t, that
means to use the current justification style for this part of the text
(see current-justification, below). Any other value is treated
as full.
When you call the filling functions interactively, using a prefix
argument implies the value full for justify.
This command fills the paragraph at or after point. If justify is non-
nil, each line is justified as well. It uses the ordinary paragraph motion commands to find paragraph boundaries. See Paragraphs.When region is non-
nil, then if Transient Mark mode is enabled and the mark is active, this command callsfill-regionto fill all the paragraphs in the region, instead of filling only the current paragraph. When this command is called interactively, region ist.
This command fills each of the paragraphs in the region from start to end. It justifies as well if justify is non-
nil.If nosqueeze is non-
nil, that means to leave whitespace other than line breaks untouched. If to-eop is non-nil, that means to keep filling to the end of the paragraph—or the next hard newline, ifuse-hard-newlinesis enabled (see below).The variable
paragraph-separatecontrols how to distinguish paragraphs. See Standard Regexps.
This command fills each paragraph in the region according to its individual fill prefix. Thus, if the lines of a paragraph were indented with spaces, the filled paragraph will remain indented in the same fashion.
The first two arguments, start and end, are the beginning and end of the region to be filled. The third and fourth arguments, justify and citation-regexp, are optional. If justify is non-
nil, the paragraphs are justified as well as filled. If citation-regexp is non-nil, it means the function is operating on a mail message and therefore should not fill the header lines. If citation-regexp is a string, it is used as a regular expression; if it matches the beginning of a line, that line is treated as a citation marker.Ordinarily,
fill-individual-paragraphsregards each change in indentation as starting a new paragraph. Iffill-individual-varying-indentis non-nil, then only separator lines separate paragraphs. That mode can handle indented paragraphs with additional indentation on the first line.
This variable alters the action of
fill-individual-paragraphsas described above.
This command considers a region of text as a single paragraph and fills it. If the region was made up of many paragraphs, the blank lines between paragraphs are removed. This function justifies as well as filling when justify is non-
nil.If nosqueeze is non-
nil, that means to leave whitespace other than line breaks untouched. If squeeze-after is non-nil, it specifies a position in the region, and means don't canonicalize spaces before that position.In Adaptive Fill mode, this command calls
fill-context-prefixto choose a fill prefix by default. See Adaptive Fill.
This command inserts spaces between the words of the current line so that the line ends exactly at
fill-column. It returnsnil.The argument how, if non-
nilspecifies explicitly the style of justification. It can beleft,right,full,center, ornone. If it ist, that means to do follow specified justification style (seecurrent-justification, below).nilmeans to do full justification.If eop is non-
nil, that means do only left-justification ifcurrent-justificationspecifies full justification. This is used for the last line of a paragraph; even if the paragraph as a whole is fully justified, the last line should not be.If nosqueeze is non-
nil, that means do not change interior whitespace.
This variable's value specifies the style of justification to use for text that doesn't specify a style with a text property. The possible values are
left,right,full,center, ornone. The default value isleft.
This function returns the proper justification style to use for filling the text around point.
This returns the value of the
justificationtext property at point, or the variable default-justification if there is no such text property. However, it returnsnilrather thannoneto mean “don't justify”.
If this variable is non-
nil, a period followed by just one space does not count as the end of a sentence, and the filling functions avoid breaking the line at such a place.
If this variable is non-
nil, a sentence can end without a period. This is used for languages like Thai, where sentences end with a double space but without a period.
If this variable is non-
nil, it should be a string of characters that can end a sentence without following spaces.
This variable provides a way to override the filling of paragraphs. If its value is non-
nil,fill-paragraphcalls this function to do the work. If the function returns a non-nilvalue,fill-paragraphassumes the job is done, and immediately returns that value.The usual use of this feature is to fill comments in programming language modes. If the function needs to fill a paragraph in the usual way, it can do so as follows:
(let ((fill-paragraph-function nil)) (fill-paragraph arg))
This variable provides a way to override how the filling functions, such as
fill-regionandfill-paragraph, move forward to the next paragraph. Its value should be a function, which is called with a single argument n, the number of paragraphs to move, and should return the difference between n and the number of paragraphs actually moved. The default value of this variable isforward-paragraph. See Paragraphs.
If this variable is non-
nil, the filling functions do not delete newlines that have thehardtext property. These hard newlines act as paragraph separators. See Hard and Soft Newlines.
This buffer-local variable, if non-
nil, specifies a string of text that appears at the beginning of normal text lines and should be disregarded when filling them. Any line that fails to start with the fill prefix is considered the start of a paragraph; so is any line that starts with the fill prefix followed by additional whitespace. Lines that start with the fill prefix but no additional whitespace are ordinary text lines that can be filled together. The resulting filled lines also start with the fill prefix.The fill prefix follows the left margin whitespace, if any.
This buffer-local variable specifies the maximum width of filled lines. Its value should be an integer, which is a number of columns. All the filling, justification, and centering commands are affected by this variable, including Auto Fill mode (see Auto Filling).
As a practical matter, if you are writing text for other people to read, you should set
fill-columnto no more than 70. Otherwise the line will be too long for people to read comfortably, and this can make the text seem clumsy.The default value for
fill-columnis 70.
This sets the
left-marginproperty on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
This sets the
right-marginproperty on the text from from to to to the value margin. If Auto Fill mode is enabled, this command also refills the region to fit the new margin.
This function returns the proper left margin value to use for filling the text around point. The value is the sum of the
left-marginproperty of the character at the start of the current line (or zero if none), and the value of the variableleft-margin.
This function returns the proper fill column value to use for filling the text around point. The value is the value of the
fill-columnvariable, minus the value of theright-marginproperty of the character after point.
This function moves point to the left margin of the current line. The column moved to is determined by calling the function
current-left-margin. If the argument n is non-nil,move-to-left-marginmoves forward n−1 lines first.If force is non-
nil, that says to fix the line's indentation if that doesn't match the left margin value.
This function removes left margin indentation from the text between from and to. The amount of indentation to delete is determined by calling
current-left-margin. In no case does this function delete non-whitespace. If from and to are omitted, they default to the whole buffer.
This function adjusts the indentation at the beginning of the current line to the value specified by the variable
left-margin. (That may involve either inserting or deleting whitespace.) This function is value ofindent-line-functionin Paragraph-Indent Text mode.
This variable specifies the base left margin column. In Fundamental mode, <RET> indents to this column. This variable automatically becomes buffer-local when set in any fashion.
This variable gives major modes a way to specify not to break a line at certain places. Its value should be a list of functions. Whenever filling considers breaking the line at a certain place in the buffer, it calls each of these functions with no arguments and with point located at that place. If any of the functions returns non-
nil, then the line won't be broken there.
When Adaptive Fill Mode is enabled, Emacs determines the fill prefix automatically from the text in each paragraph being filled rather than using a predetermined value. During filling, this fill prefix gets inserted at the start of the second and subsequent lines of the paragraph as described in Filling, and in Auto Filling.
Adaptive Fill mode is enabled when this variable is non-
nil. It istby default.
This function implements the heart of Adaptive Fill mode; it chooses a fill prefix based on the text between from and to, typically the start and end of a paragraph. It does this by looking at the first two lines of the paragraph, based on the variables described below.
Usually, this function returns the fill prefix, a string. However, before doing this, the function makes a final check (not specially mentioned in the following) that a line starting with this prefix wouldn't look like the start of a paragraph. Should this happen, the function signals the anomaly by returning
nilinstead.In detail,
fill-context-prefixdoes this:
- It takes a candidate for the fill prefix from the first line—it tries first the function in
adaptive-fill-function(if any), then the regular expressionadaptive-fill-regexp(see below). The first non-nilresult of these, or the empty string if they're bothnil, becomes the first line's candidate.- If the paragraph has as yet only one line, the function tests the validity of the prefix candidate just found. The function then returns the candidate if it's valid, or a string of spaces otherwise. (see the description of
adaptive-fill-first-line-regexpbelow).- When the paragraph already has two lines, the function next looks for a prefix candidate on the second line, in just the same way it did for the first line. If it doesn't find one, it returns
nil.- The function now compares the two candidate prefixes heuristically: if the non-whitespace characters in the line 2 candidate occur in the same order in the line 1 candidate, the function returns the line 2 candidate. Otherwise, it returns the largest initial substring which is common to both candidates (which might be the empty string).
Adaptive Fill mode matches this regular expression against the text starting after the left margin whitespace (if any) on a line; the characters it matches are that line's candidate for the fill prefix.
The default value matches whitespace with certain punctuation characters intermingled.
Used only in one-line paragraphs, this regular expression acts as an additional check of the validity of the one available candidate fill prefix: the candidate must match this regular expression, or match
comment-start-skip. If it doesn't,fill-context-prefixreplaces the candidate with a string of spaces of the same width as it.The default value of this variable is
"\\`[ \t]*\\'", which matches only a string of whitespace. The effect of this default is to force the fill prefixes found in one-line paragraphs always to be pure whitespace.
You can specify more complex ways of choosing a fill prefix automatically by setting this variable to a function. The function is called with point after the left margin (if any) of a line, and it must preserve point. It should return either that line's fill prefix or
nil, meaning it has failed to determine a prefix.
Auto Fill mode is a minor mode that fills lines automatically as text is inserted. This section describes the hook used by Auto Fill mode. For a description of functions that you can call explicitly to fill and justify existing text, see Filling.
Auto Fill mode also enables the functions that change the margins and justification style to refill portions of the text. See Margins.
The value of this buffer-local variable should be a function (of no arguments) to be called after self-inserting a character from the table
auto-fill-chars. It may benil, in which case nothing special is done in that case.The value of
auto-fill-functionisdo-auto-fillwhen Auto-Fill mode is enabled. That is a function whose sole purpose is to implement the usual strategy for breaking a line.
This variable specifies the function to use for
auto-fill-function, if and when Auto Fill is turned on. Major modes can set buffer-local values for this variable to alter how Auto Fill works.
A char table of characters which invoke
auto-fill-functionwhen self-inserted—space and newline in most language environments. They have an entrytin the table.
The sorting functions described in this section all rearrange text in
a buffer. This is in contrast to the function sort, which
rearranges the order of the elements of a list (see Rearrangement).
The values returned by these functions are not meaningful.
This function is the general text-sorting routine that subdivides a buffer into records and then sorts them. Most of the commands in this section use this function.
To understand how
sort-subrworks, consider the whole accessible portion of the buffer as being divided into disjoint pieces called sort records. The records may or may not be contiguous, but they must not overlap. A portion of each sort record (perhaps all of it) is designated as the sort key. Sorting rearranges the records in order by their sort keys.Usually, the records are rearranged in order of ascending sort key. If the first argument to the
sort-subrfunction, reverse, is non-nil, the sort records are rearranged in order of descending sort key.The next four arguments to
sort-subrare functions that are called to move point across a sort record. They are called many times from withinsort-subr.
- nextrecfun is called with point at the end of a record. This function moves point to the start of the next record. The first record is assumed to start at the position of point when
sort-subris called. Therefore, you should usually move point to the beginning of the buffer before callingsort-subr.This function can indicate there are no more sort records by leaving point at the end of the buffer.
- endrecfun is called with point within a record. It moves point to the end of the record.
- startkeyfun is called to move point from the start of a record to the start of the sort key. This argument is optional; if it is omitted, the whole record is the sort key. If supplied, the function should either return a non-
nilvalue to be used as the sort key, or returnnilto indicate that the sort key is in the buffer starting at point. In the latter case, endkeyfun is called to find the end of the sort key.- endkeyfun is called to move point from the start of the sort key to the end of the sort key. This argument is optional. If startkeyfun returns
niland this argument is omitted (ornil), then the sort key extends to the end of the record. There is no need for endkeyfun if startkeyfun returns a non-nilvalue.The argument predicate is the function to use to compare keys. If keys are numbers, it defaults to
<; otherwise it defaults tostring<.As an example of
sort-subr, here is the complete function definition forsort-lines:;; Note that the first two lines of doc string ;; are effectively one line when viewed by a user. (defun sort-lines (reverse beg end) "Sort lines in region alphabetically;\ argument means descending order. Called from a program, there are three arguments: REVERSE (non-nil means reverse order),\ BEG and END (region to sort). The variable `sort-fold-case' determines\ whether alphabetic case affects the sort order." (interactive "P\nr") (save-excursion (save-restriction (narrow-to-region beg end) (goto-char (point-min)) (let ((inhibit-field-text-motion t)) (sort-subr reverse 'forward-line 'end-of-line)))))Here
forward-linemoves point to the start of the next record, andend-of-linemoves point to the end of record. We do not pass the arguments startkeyfun and endkeyfun, because the entire record is used as the sort key.The
sort-paragraphsfunction is very much the same, except that itssort-subrcall looks like this:(sort-subr reverse (function (lambda () (while (and (not (eobp)) (looking-at paragraph-separate)) (forward-line 1)))) 'forward-paragraph)Markers pointing into any sort records are left with no useful position after
sort-subrreturns.
If this variable is non-
nil,sort-subrand the other buffer sorting functions ignore case when comparing strings.
This command sorts the region between start and end alphabetically as specified by record-regexp and key-regexp. If reverse is a negative integer, then sorting is in reverse order.
Alphabetical sorting means that two sort keys are compared by comparing the first characters of each, the second characters of each, and so on. If a mismatch is found, it means that the sort keys are unequal; the sort key whose character is less at the point of first mismatch is the lesser sort key. The individual characters are compared according to their numerical character codes in the Emacs character set.
The value of the record-regexp argument specifies how to divide the buffer into sort records. At the end of each record, a search is done for this regular expression, and the text that matches it is taken as the next record. For example, the regular expression `^.+$', which matches lines with at least one character besides a newline, would make each such line into a sort record. See Regular Expressions, for a description of the syntax and meaning of regular expressions.
The value of the key-regexp argument specifies what part of each record is the sort key. The key-regexp could match the whole record, or only a part. In the latter case, the rest of the record has no effect on the sorted order of records, but it is carried along when the record moves to its new position.
The key-regexp argument can refer to the text matched by a subexpression of record-regexp, or it can be a regular expression on its own.
If key-regexp is:
- `\digit'
- then the text matched by the digitth `\(...\)' parenthesis grouping in record-regexp is the sort key.
- `\&'
- then the whole record is the sort key.
- a regular expression
- then
sort-regexp-fieldssearches for a match for the regular expression within the record. If such a match is found, it is the sort key. If there is no match for key-regexp within a record then that record is ignored, which means its position in the buffer is not changed. (The other records may move around it.)For example, if you plan to sort all the lines in the region by the first word on each line starting with the letter `f', you should set record-regexp to `^.*$' and set key-regexp to `\<f\w*\>'. The resulting expression looks like this:
(sort-regexp-fields nil "^.*$" "\\<f\\w*\\>" (region-beginning) (region-end))If you call
sort-regexp-fieldsinteractively, it prompts for record-regexp and key-regexp in the minibuffer.
This command alphabetically sorts lines in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command alphabetically sorts paragraphs in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command alphabetically sorts pages in the region between start and end. If reverse is non-
nil, the sort is in reverse order.
This command sorts lines in the region between start and end, comparing them alphabetically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.
This command sorts lines in the region between start and end, comparing them numerically by the fieldth field of each line. Fields are separated by whitespace and numbered starting from 1. The specified field must contain a number in each line of the region. Numbers starting with 0 are treated as octal, and numbers starting with `0x' are treated as hexadecimal.
If field is negative, sorting is by the −fieldth field from the end of the line. This command is useful for sorting tables.
This variable specifies the default radix for
sort-numeric-fieldsto parse numbers.
This command sorts the lines in the region between beg and end, comparing them alphabetically by a certain range of columns. The column positions of beg and end bound the range of columns to sort on.
If reverse is non-
nil, the sort is in reverse order.One unusual thing about this command is that the entire line containing position beg, and the entire line containing position end, are included in the region sorted.
Note that
sort-columnsrejects text that contains tabs, because tabs could be split across the specified columns. Use M-x untabify to convert tabs to spaces before sorting.When possible, this command actually works by calling the
sortutility program.
The column functions convert between a character position (counting characters from the beginning of the buffer) and a column position (counting screen characters from the beginning of a line).
These functions count each character according to the number of
columns it occupies on the screen. This means control characters count
as occupying 2 or 4 columns, depending upon the value of
ctl-arrow, and tabs count as occupying a number of columns that
depends on the value of tab-width and on the column where the tab
begins. See Usual Display.
Column number computations ignore the width of the window and the amount of horizontal scrolling. Consequently, a column value can be arbitrarily high. The first (or leftmost) column is numbered 0. They also ignore overlays and text properties, aside from invisibility.
This function returns the horizontal position of point, measured in columns, counting from 0 at the left margin. The column position is the sum of the widths of all the displayed representations of the characters between the start of the current line and point.
This function moves point to column in the current line. The calculation of column takes into account the widths of the displayed representations of the characters between the start of the line and point.
When called interactively, column is the value of prefix numeric argument. If column is not an integer, an error is signaled.
If it is impossible to move to column column because that is in the middle of a multicolumn character such as a tab, point moves to the end of that character. However, if force is non-
nil, and column is in the middle of a tab, thenmove-to-columnconverts the tab into spaces so that it can move precisely to column column. Other multicolumn characters can cause anomalies despite force, since there is no way to split them.The argument force also has an effect if the line isn't long enough to reach column column; if it is
t, that means to add whitespace at the end of the line to reach that column.The return value is the column number actually moved to.
The indentation functions are used to examine, move to, and change whitespace that is at the beginning of a line. Some of the functions can also change whitespace elsewhere on a line. Columns and indentation count from zero at the left margin.
This section describes the primitive functions used to count and insert indentation. The functions in the following sections use these primitives. See Size of Displayed Text, for related functions.
This function returns the indentation of the current line, which is the horizontal position of the first nonblank character. If the contents are entirely blank, then this is the horizontal position of the end of the line.
This function indents from point with tabs and spaces until column is reached. If minimum is specified and non-
nil, then at least that many spaces are inserted even if this requires going beyond column. Otherwise the function does nothing if point is already beyond column. The value is the column at which the inserted indentation ends.The inserted whitespace characters inherit text properties from the surrounding text (usually, from the preceding text only). See Sticky Properties.
If this variable is non-
nil, indentation functions can insert tabs as well as spaces. Otherwise, they insert only spaces. Setting this variable automatically makes it buffer-local in the current buffer.
An important function of each major mode is to customize the <TAB> key to indent properly for the language being edited. This section describes the mechanism of the <TAB> key and how to control it. The functions in this section return unpredictable values.
This is the command bound to <TAB> in most editing modes. Its usual action is to indent the current line, but it can alternatively insert a tab character or indent a region.
Here is what it does:
- First, it checks whether Transient Mark mode is enabled and the region is active. If so, it called
indent-regionto indent all the text in the region (see Region Indent).- Otherwise, if the indentation function in
indent-line-functionisindent-to-left-margin(a trivial command that inserts a tab character), or if the variabletab-always-indentspecifies that a tab character ought to be inserted (see below), then it inserts a tab character.- Otherwise, it indents the current line; this is done by calling the function in
indent-line-function. If the line is already indented, and the value oftab-always-indentiscomplete(see below), it tries completing the text at point.If rigid is non-
nil(interactively, with a prefix argument), then after this command indents a line or inserts a tab, it also rigidly indents the entire balanced expression which starts at the beginning of the current line, in order to reflect the new indentation. This argument is ignored if the command indents the region.
This variable's value is the function to be used by
indent-for-tab-command, and various other indentation commands, to indent the current line. It is usually assigned by the major mode; for instance, Lisp mode sets it tolisp-indent-line, C mode sets it toc-indent-line, and so on. The default value isindent-relative. See Auto-Indentation.
This command calls the function in
indent-line-functionto indent the current line in a way appropriate for the current major mode.
This function inserts a newline, then indents the new line (the one following the newline just inserted) according to the major mode. It does indentation by calling
indent-according-to-mode.
This command reindents the current line, inserts a newline at point, and then indents the new line (the one following the newline just inserted). It does indentation on both lines by calling
indent-according-to-mode.
This variable can be used to customize the behavior of the <TAB> (
indent-for-tab-command) command. If the value ist(the default), the command normally just indents the current line. If the value isnil, the command indents the current line only if point is at the left margin or in the line's indentation; otherwise, it inserts a tab character. If the value iscomplete, the command first tries to indent the current line, and if the line was already indented, it callscompletion-at-pointto complete the text at point (see Completion in Buffers).
This section describes commands that indent all the lines in the region. They return unpredictable values.
This command indents each nonblank line starting between start (inclusive) and end (exclusive). If to-column is
nil,indent-regionindents each nonblank line by calling the current mode's indentation function, the value ofindent-line-function.If to-column is non-
nil, it should be an integer specifying the number of columns of indentation; then this function gives each line exactly that much indentation, by either adding or deleting whitespace.If there is a fill prefix,
indent-regionindents each line by making it start with the fill prefix.
The value of this variable is a function that can be used by
indent-regionas a short cut. It should take two arguments, the start and end of the region. You should design the function so that it will produce the same results as indenting the lines of the region one by one, but presumably faster.If the value is
nil, there is no short cut, andindent-regionactually works line by line.A short-cut function is useful in modes such as C mode and Lisp mode, where the
indent-line-functionmust scan from the beginning of the function definition: applying it to each line would be quadratic in time. The short cut can update the scan information as it moves through the lines indenting them; this takes linear time. In a mode where indenting a line individually is fast, there is no need for a short cut.
indent-regionwith a non-nilargument to-column has a different meaning and does not use this variable.
This function indents all lines starting between start (inclusive) and end (exclusive) sideways by count columns. This preserves the shape of the affected region, moving it as a rigid unit.
This is useful not only for indenting regions of unindented text, but also for indenting regions of formatted code. For example, if count is 3, this command adds 3 columns of indentation to every line that begins in the specified region.
If called interactively with no prefix argument, this command invokes a transient mode for adjusting indentation rigidly. See Indentation Commands.
This is like
indent-rigidly, except that it doesn't alter lines that start within strings or comments.In addition, it doesn't alter a line if nochange-regexp matches at the beginning of the line (if nochange-regexp is non-
nil).
This section describes two commands that indent the current line based on the contents of previous lines.
This command inserts whitespace at point, extending to the same column as the next indent point of the previous nonblank line. An indent point is a non-whitespace character following whitespace. The next indent point is the first one at a column greater than the current column of point. For example, if point is underneath and to the left of the first non-blank character of a line of text, it moves to that column by inserting whitespace.
If the previous nonblank line has no next indent point (i.e., none at a great enough column position),
indent-relativeeither does nothing (if unindented-ok is non-nil) or callstab-to-tab-stop. Thus, if point is underneath and to the right of the last column of a short line of text, this command ordinarily moves point to the next tab stop by inserting whitespace.The return value of
indent-relativeis unpredictable.In the following example, point is at the beginning of the second line:
This line is indented twelve spaces. -!-The quick brown fox jumped.Evaluation of the expression
(indent-relative nil)produces the following:This line is indented twelve spaces. -!-The quick brown fox jumped.In this next example, point is between the `m' and `p' of `jumped':
This line is indented twelve spaces. The quick brown fox jum-!-ped.Evaluation of the expression
(indent-relative nil)produces the following:This line is indented twelve spaces. The quick brown fox jum -!-ped.
This command indents the current line like the previous nonblank line, by calling
indent-relativewithtas the unindented-ok argument. The return value is unpredictable.If the previous nonblank line has no indent points beyond the current column, this command does nothing.
This section explains the mechanism for user-specified tab stops and the mechanisms that use and set them. The name “tab stops” is used because the feature is similar to that of the tab stops on a typewriter. The feature works by inserting an appropriate number of spaces and tab characters to reach the next tab stop column; it does not affect the display of tab characters in the buffer (see Usual Display). Note that the <TAB> character as input uses this tab stop feature only in a few major modes, such as Text mode. See Tab Stops.
This command inserts spaces or tabs before point, up to the next tab stop column defined by
tab-stop-list.
This variable defines the tab stop columns used by
tab-to-tab-stop. It should be eithernil, or a list of increasing integers, which need not be evenly spaced. The list is implicitly extended to infinity through repetition of the interval between the last and penultimate elements (ortab-widthif the list has fewer than two elements). A value ofnilmeans a tab stop everytab-widthcolumns.Use M-x edit-tab-stops to edit the location of tab stops interactively.
These commands, primarily for interactive use, act based on the indentation in the text.
This command moves point to the first non-whitespace character in the current line (which is the line in which point is located). It returns
nil.
This command moves point backward arg lines and then to the first nonblank character on that line. It returns
nil. If arg is omitted ornil, it defaults to 1.
This command moves point forward arg lines and then to the first nonblank character on that line. It returns
nil. If arg is omitted ornil, it defaults to 1.
The case change commands described here work on text in the current buffer. See Case Conversion, for case conversion functions that work on strings and characters. See Case Tables, for how to customize which characters are upper or lower case and how to convert them.
This function capitalizes all words in the region defined by start and end. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. The function returns
nil.If one end of the region is in the middle of a word, the part of the word within the region is treated as an entire word.
When
capitalize-regionis called interactively, start and end are point and the mark, with the smallest first.---------- Buffer: foo ---------- This is the contents of the 5th foo. ---------- Buffer: foo ---------- (capitalize-region 1 37) => nil ---------- Buffer: foo ---------- This Is The Contents Of The 5th Foo. ---------- Buffer: foo ----------
This function converts all of the letters in the region defined by start and end to lower case. The function returns
nil.When
downcase-regionis called interactively, start and end are point and the mark, with the smallest first.
This function converts all of the letters in the region defined by start and end to upper case. The function returns
nil.When
upcase-regionis called interactively, start and end are point and the mark, with the smallest first.
This function capitalizes count words after point, moving point over as it does. To capitalize means to convert each word's first character to upper case and convert the rest of each word to lower case. If count is negative, the function capitalizes the −count previous words but does not move point. The value is
nil.If point is in the middle of a word, the part of the word before point is ignored when moving forward. The rest is treated as an entire word.
When
capitalize-wordis called interactively, count is set to the numeric prefix argument.
This function converts the count words after point to all lower case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is
nil.When
downcase-wordis called interactively, count is set to the numeric prefix argument.
This function converts the count words after point to all upper case, moving point over as it does. If count is negative, it converts the −count previous words but does not move point. The value is
nil.When
upcase-wordis called interactively, count is set to the numeric prefix argument.
Each character position in a buffer or a string can have a text property list, much like the property list of a symbol (see Property Lists). The properties belong to a particular character at a particular place, such as, the letter `T' at the beginning of this sentence or the first `o' in `foo'—if the same character occurs in two different places, the two occurrences in general have different properties.
Each property has a name and a value. Both of these can be any Lisp
object, but the name is normally a symbol. Typically each property
name symbol is used for a particular purpose; for instance, the text
property face specifies the faces for displaying the character
(see Special Properties). The usual way to access the property
list is to specify a name and ask what value corresponds to it.
If a character has a category property, we call it the
property category of the character. It should be a symbol. The
properties of the symbol serve as defaults for the properties of the
character.
Copying text between strings and buffers preserves the properties
along with the characters; this includes such diverse functions as
substring, insert, and buffer-substring.
The simplest way to examine text properties is to ask for the value of
a particular property of a particular character. For that, use
get-text-property. Use text-properties-at to get the
entire property list of a character. See Property Search, for
functions to examine the properties of a number of characters at once.
These functions handle both strings and buffers. Keep in mind that positions in a string start from 0, whereas positions in a buffer start from 1.
This function returns the value of the prop property of the character after position pos in object (a buffer or string). The argument object is optional and defaults to the current buffer.
If there is no prop property strictly speaking, but the character has a property category that is a symbol, then
get-text-propertyreturns the prop property of that symbol.
This function is like
get-text-property, except that it checks overlays first and then text properties. See Overlays.The argument object may be a string, a buffer, or a window. If it is a window, then the buffer displayed in that window is used for text properties and overlays, but only the overlays active for that window are considered. If object is a buffer, then overlays in that buffer are considered first, in order of decreasing priority, followed by the text properties. If object is a string, only text properties are considered, since strings never have overlays.
This function is like
get-char-property, except that it pays attention to properties' stickiness and overlays' advancement settings instead of the property of the character at (i.e., right after) position.
This is like
get-char-property, but gives extra information about the overlay that the property value comes from.Its value is a cons cell whose car is the property value, the same value
get-char-propertywould return with the same arguments. Its cdr is the overlay in which the property was found, ornil, if it was found as a text property or not found at all.If position is at the end of object, both the car and the cdr of the value are
nil.
This variable holds an alist which maps property names to a list of alternative property names. If a character does not specify a direct value for a property, the alternative property names are consulted in order; the first non-
nilvalue is used. This variable takes precedence overdefault-text-properties, andcategoryproperties take precedence over this variable.
This function returns the entire property list of the character at position in the string or buffer object. If object is
nil, it defaults to the current buffer.
This variable holds a property list giving default values for text properties. Whenever a character does not specify a value for a property, neither directly, through a category symbol, or through
char-property-alias-alist, the value stored in this list is used instead. Here is an example:(setq default-text-properties '(foo 69) char-property-alias-alist nil) ;; Make sure character 1 has no properties of its own. (set-text-properties 1 2 nil) ;; What we get, when we ask, is the default value. (get-text-property 1 'foo) => 69
The primitives for changing properties apply to a specified range of
text in a buffer or string. The function set-text-properties
(see end of section) sets the entire property list of the text in that
range; more often, it is useful to add, change, or delete just certain
properties specified by name.
Since text properties are considered part of the contents of the buffer (or string), and can affect how a buffer looks on the screen, any change in buffer text properties marks the buffer as modified. Buffer text property changes are undoable also (see Undo). Positions in a string start from 0, whereas positions in a buffer start from 1.
This function sets the prop property to value for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.
This function adds or overrides text properties for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props specifies which properties to add. It should have the form of a property list (see Property Lists): a list whose elements include the property names followed alternately by the corresponding values.
The return value is
tif the function actually changed some property's value;nilotherwise (if props isnilor its values agree with those in the text).For example, here is how to set the
commentandfaceproperties of a range of text:(add-text-properties start end '(comment t face highlight))
This function deletes specified text properties from the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props specifies which properties to delete. It should have the form of a property list (see Property Lists): a list whose elements are property names alternating with corresponding values. But only the names matter—the values that accompany them are ignored. For example, here's how to remove the
faceproperty.(remove-text-properties start end '(face nil))The return value is
tif the function actually changed some property's value;nilotherwise (if props isnilor if no character in the specified text had any of those properties).To remove all text properties from certain text, use
set-text-propertiesand specifynilfor the new property list.
Like
remove-text-propertiesexcept that list-of-properties is a list of property names only, not an alternating list of property names and values.
This function completely replaces the text property list for the text between start and end in the string or buffer object. If object is
nil, it defaults to the current buffer.The argument props is the new property list. It should be a list whose elements are property names alternating with corresponding values.
After
set-text-propertiesreturns, all the characters in the specified range have identical properties.If props is
nil, the effect is to get rid of all properties from the specified range of text. Here's an example:(set-text-properties start end nil)Do not rely on the return value of this function.
This function acts on the text between start and end, adding the face face to the
facetext property. face should be a valid value for thefaceproperty (see Special Properties), such as a face name or an anonymous face (see Faces).If any text in the region already has a non-
nilfaceproperty, those face(s) are retained. This function sets thefaceproperty to a list of faces, with face as the first element (by default) and the pre-existing faces as the remaining elements. If the optional argument append is non-nil, face is appended to the end of the list instead. Note that in a face list, the first occurring value for each attribute takes precedence.For example, the following code would assign a italicized green face to the text between start and end:
(add-face-text-property start end 'italic) (add-face-text-property start end '(:foreground "red")) (add-face-text-property start end '(:foreground "green"))The optional argument object, if non-
nil, specifies a buffer or string to act on, rather than the current buffer. If object is a string, then start and end are zero-based indices into the string.
The easiest way to make a string with text properties is with
propertize:
This function returns a copy of string with the text properties properties added. These properties apply to all the characters in the string that is returned. Here is an example that constructs a string with a
faceproperty and amouse-faceproperty:(propertize "foo" 'face 'italic 'mouse-face 'bold-italic) => #("foo" 0 3 (mouse-face bold-italic face italic))To put different properties on various parts of a string, you can construct each part with
propertizeand then combine them withconcat:(concat (propertize "foo" 'face 'italic 'mouse-face 'bold-italic) " and " (propertize "bar" 'face 'italic 'mouse-face 'bold-italic)) => #("foo and bar" 0 3 (face italic mouse-face bold-italic) 3 8 nil 8 11 (face italic mouse-face bold-italic))
See Buffer Contents, for the function
buffer-substring-no-properties, which copies text from the
buffer but does not copy its properties.
If you wish to add or remove text properties to a buffer without
marking the buffer as modified, you can wrap the calls above in the
with-silent-modifications macro.
In typical use of text properties, most of the time several or many consecutive characters have the same value for a property. Rather than writing your programs to examine characters one by one, it is much faster to process chunks of text that have the same property value.
Here are functions you can use to do this. They use eq for
comparing property values. In all cases, object defaults to the
current buffer.
For good performance, it's very important to use the limit argument to these functions, especially the ones that search for a single property—otherwise, they may spend a long time scanning to the end of the buffer, if the property you are interested in does not change.
These functions do not move point; instead, they return a position (or
nil). Remember that a position is always between two characters;
the position returned by these functions is between two characters with
different properties.
The function scans the text forward from position pos in the string or buffer object until it finds a change in some text property, then returns the position of the change. In other words, it returns the position of the first character beyond pos whose properties are not identical to those of the character just after pos.
If limit is non-
nil, then the scan ends at position limit. If there is no property change before that point, this function returns limit.The value is
nilif the properties remain unchanged all the way to the end of object and limit isnil. If the value is non-nil, it is a position greater than or equal to pos. The value equals pos only when limit equals pos.Here is an example of how to scan the buffer by chunks of text within which all properties are constant:
(while (not (eobp)) (let ((plist (text-properties-at (point))) (next-change (or (next-property-change (point) (current-buffer)) (point-max)))) Process text from point to next-change... (goto-char next-change)))
This is like
next-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.
The function scans text for a change in the prop property, then returns the position of the change. The scan goes forward from position pos in the string or buffer object. In other words, this function returns the position of the first character beyond pos whose prop property differs from that of the character just after pos.
If limit is non-
nil, then the scan ends at position limit. If there is no property change before that point,next-single-property-changereturns limit.The value is
nilif the property remains unchanged all the way to the end of object and limit isnil. If the value is non-nil, it is a position greater than or equal to pos; it equals pos only if limit equals pos.
This is like
next-single-property-change, but scans back from pos instead of forward. If the value is non-nil, it is a position less than or equal to pos; it equals pos only if limit equals pos.
This is like
next-property-changeexcept that it considers overlay properties as well as text properties, and if no change is found before the end of the buffer, it returns the maximum buffer position rather thannil(in this sense, it resembles the corresponding overlay functionnext-overlay-change, rather thannext-property-change). There is no object operand because this function operates only on the current buffer. It returns the next address at which either kind of property changes.
This is like
next-char-property-change, but scans back from pos instead of forward, and returns the minimum buffer position if no change is found.
This is like
next-single-property-changeexcept that it considers overlay properties as well as text properties, and if no change is found before the end of the object, it returns the maximum valid position in object rather thannil. Unlikenext-char-property-change, this function does have an object operand; if object is not a buffer, only text-properties are considered.
This is like
next-single-char-property-change, but scans back from pos instead of forward, and returns the minimum valid position in object if no change is found.
This function returns non-
nilif at least one character between start and end has a property prop whose value is value. More precisely, it returns the position of the first such character. Otherwise, it returnsnil.The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
This function returns non-
nilif at least one character between start and end does not have a property prop with value value. More precisely, it returns the position of the first such character. Otherwise, it returnsnil.The optional fifth argument, object, specifies the string or buffer to scan. Positions are relative to object. The default for object is the current buffer.
Here is a table of text property names that have special built-in meanings. The following sections list a few additional special property names that control filling and property inheritance. All other names have no standard meaning, and you can use them as you like.
Note: the properties composition, display,
invisible and intangible can also cause point to move to
an acceptable place, after each Emacs command. See Adjusting Point.
categorycategory property, we call it the
property category of the character. It should be a symbol. The
properties of this symbol serve as defaults for the properties of the
character.
faceface property controls the appearance of the character
(see Faces). The value of the property can be the following:
(keyword
value ...), where each keyword is a face attribute
name and value is a value for that attribute.
(foreground-color . color-name)
or (background-color . color-name). This specifies the
foreground or background color, similar to (:foreground
color-name) or (:background color-name). This
form is supported for backward compatibility only, and should be
avoided.
Font Lock mode (see Font Lock Mode) works in most buffers by
dynamically updating the face property of characters based on
the context.
The add-face-text-property function provides a convenient way
to set this text property. See Changing Properties.
font-lock-faceface property that Font
Lock mode should apply to the underlying text. It is one of the
fontification methods used by Font Lock mode, and is useful for
special modes that implement their own highlighting.
See Precalculated Fontification. When Font Lock mode is disabled,
font-lock-face has no effect.
mouse-faceface when the mouse is on or
near the character. For this purpose, “near” means that all text
between the character and where the mouse is have the same
mouse-face property value.
Emacs ignores all face attributes from the mouse-face property
that alter the text size (e.g., :height, :weight, and
:slant). Those attributes are always the same as for the
unhighlighted text.
fontifiednil, Emacs's redisplay routine calls the functions in
fontification-functions (see Auto Faces) to prepare this
part of the buffer before it is displayed. It is used internally by
the just-in-time font locking code.
displayhelp-echohelp-echo property, then when you
move the mouse onto that text, Emacs displays that string in the echo
area, or in the tooltip window (see Tooltips).
If the value of the help-echo property is a function, that
function is called with three arguments, window, object and
pos and should return a help string or nil for
none. The first argument, window is the window in which
the help was found. The second, object, is the buffer, overlay or
string which had the help-echo property. The pos
argument is as follows:
help-echo
property, and pos is the position in the overlay's buffer.
display property), pos is the position in that
string.
If the value of the help-echo property is neither a function nor
a string, it is evaluated to obtain a help string.
You can alter the way help text is displayed by setting the variable
show-help-function (see Help display).
This feature is used in the mode line and for other active text.
keymapkeymap property specifies an additional keymap for
commands. When this keymap applies, it is used for key lookup before
the minor mode keymaps and before the buffer's local map.
See Active Keymaps. If the property value is a symbol, the
symbol's function definition is used as the keymap.
The property's value for the character before point applies if it is
non-nil and rear-sticky, and the property's value for the
character after point applies if it is non-nil and
front-sticky. (For mouse clicks, the position of the click is used
instead of the position of point.)
local-mapkeymap except that it specifies a
keymap to use instead of the buffer's local map. For most
purposes (perhaps all purposes), it is better to use the keymap
property.
syntax-tablesyntax-table property overrides what the syntax table says
about this particular character. See Syntax Properties.
read-onlyread-only, then modifying that
character is not allowed. Any command that would do so gets an error,
text-read-only. If the property value is a string, that string
is used as the error message.
Insertion next to a read-only character is an error if inserting
ordinary text there would inherit the read-only property due to
stickiness. Thus, you can control permission to insert next to
read-only text by controlling the stickiness. See Sticky Properties.
Since changing properties counts as modifying the buffer, it is not
possible to remove a read-only property unless you know the
special trick: bind inhibit-read-only to a non-nil value
and then remove the property. See Read Only Buffers.
inhibit-read-onlyinhibit-read-only can be
edited even in read-only buffers. See Read Only Buffers.
invisiblenil invisible property can make a character invisible
on the screen. See Invisible Text, for details.
intangiblenil
intangible properties, then you cannot place point between them.
If you try to move point forward into the group, point actually moves to
the end of the group. If you try to move point backward into the group,
point actually moves to the start of the group.
If consecutive characters have unequal non-nil
intangible properties, they belong to separate groups; each
group is separately treated as described above.
When the variable inhibit-point-motion-hooks is non-nil
(as it is by default), the intangible property is ignored.
Beware: this property operates at a very low level, and affects a lot of code
in unexpected ways. So use it with extreme caution. A common misuse is to put
an intangible property on invisible text, which is actually unnecessary since
the command loop will move point outside of the invisible text at the end of
each command anyway. See Adjusting Point. For these reasons, this
property is obsolete; use the cursor-intangible property instead.
cursor-intangiblecursor-intangible-mode is turned on, point
is moved away of any position that has a non-nil
cursor-intangible property, just before redisplay happens.
fieldfield property constitute a
field. Some motion functions including forward-word and
beginning-of-line stop moving at a field boundary.
See Fields.
cursornil cursor text
property. In addition, if the value of the cursor property is
an integer, it specifies the number of buffer's character
positions, starting with the position where the overlay or the
display property begins, for which the cursor should be
displayed on that character. Specifically, if the value of the
cursor property of a character is the number n, the
cursor will be displayed on this character for any buffer position in
the range [ovpos..ovpos+n), where ovpos
is the overlay's starting position given by overlay-start
(see Managing Overlays), or the position where the display
text property begins in the buffer.
In other words, the string character with the cursor property
of any non-nil value is the character where to display the
cursor. The value of the property says for which buffer positions to
display the cursor there. If the value is an integer n,
the cursor is displayed there when point is anywhere between the
beginning of the overlay or display property and n
positions after that. If the value is anything else and
non-nil, the cursor is displayed there only when point is at
the beginning of the display property or at
overlay-start.
When the buffer has many overlay strings (e.g., see before-string) or display properties that are
strings, it is a good idea to use the cursor property on these
strings to cue the Emacs display about the places where to put the
cursor while traversing these strings. This directly communicates to
the display engine where the Lisp program wants to put the cursor, or
where the user would expect the cursor.
pointerline-spacingline-spacing text or overlay property that
controls the height of the display line ending with that newline. The
property value overrides the default frame line spacing and the buffer
local line-spacing variable. See Line Height.
line-heightline-height text or overlay property that
controls the total height of the display line ending in that newline.
See Line Height.
wrap-prefixwrap-prefix property, the prefix it defines will
be added at display time to the beginning of every continuation line
due to text wrapping (so if lines are truncated, the wrap-prefix is
never used). It may be a string or an image (see Other Display Specs), or a stretch of whitespace such as specified by the
:width or :align-to display properties (see Specified Space).
A wrap-prefix may also be specified for an entire buffer using the
wrap-prefix buffer-local variable (however, a
wrap-prefix text-property takes precedence over the value of
the wrap-prefix variable). See Truncation.
line-prefixline-prefix property, the prefix it defines will
be added at display time to the beginning of every non-continuation
line. It may be a string or an image (see Other Display Specs), or a stretch of whitespace such as specified by the
:width or :align-to display properties (see Specified Space).
A line-prefix may also be specified for an entire buffer using the
line-prefix buffer-local variable (however, a
line-prefix text-property takes precedence over the value of
the line-prefix variable). See Truncation.
modification-hooksmodification-hooks, then its
value should be a list of functions; modifying that character calls
all of those functions before the actual modification. Each function
receives two arguments: the beginning and end of the part of the
buffer being modified. Note that if a particular modification hook
function appears on several characters being modified by a single
primitive, you can't predict how many times the function will
be called.
Furthermore, insertion will not modify any existing character, so this
hook will only be run when removing some characters, replacing them
with others, or changing their text-properties.
If these functions modify the buffer, they should bind
inhibit-modification-hooks to t around doing so, to
avoid confusing the internal mechanism that calls these hooks.
Overlays also support the modification-hooks property, but the
details are somewhat different (see Overlay Properties).
insert-in-front-hooksinsert-behind-hooksinsert-in-front-hooks property of the following
character and in the insert-behind-hooks property of the
preceding character. These functions receive two arguments, the
beginning and end of the inserted text. The functions are called
after the actual insertion takes place.
See also Change Hooks, for other hooks that are called
when you change text in a buffer.
point-enteredpoint-leftpoint-entered and point-left
record hook functions that report motion of point. Each time point
moves, Emacs compares these two property values:
point-left property of the character after the old location,
and
point-entered property of the character after the new
location.
If these two values differ, each of them is called (if not nil)
with two arguments: the old value of point, and the new one.
The same comparison is made for the characters before the old and new
locations. The result may be to execute two point-left functions
(which may be the same function) and/or two point-entered
functions (which may be the same function). In any case, all the
point-left functions are called first, followed by all the
point-entered functions.
It is possible to use char-after to examine characters at various
buffer positions without moving point to those positions. Only an
actual change in the value of point runs these hook functions.
The variable inhibit-point-motion-hooks by default inhibits
running the point-left and point-entered hooks, see
Inhibit point motion hooks.
These properties are obsolete; please use
cursor-sensor-functions instead.
cursor-sensor-functionsentered or left,
depending on whether the cursor is entering the text that has this
property or leaving it. The functions are called only when the minor
mode cursor-sensor-mode is turned on.
compositionput-text-property.
When this obsolete variable is non-
nil,point-leftandpoint-enteredhooks are not run, and theintangibleproperty has no effect. Do not set this variable globally; bind it withlet. Since the affected properties are obsolete, this variable's default value ist, to effectively disable them.
If this variable is non-
nil, it specifies a function called to display help strings. These may behelp-echoproperties, menu help strings (see Simple Menu Items, see Extended Menu Items), or tool bar help strings (see Tool Bar). The specified function is called with one argument, the help string to display, which is passed throughsubstitute-command-keysbefore being given to the function; see Keys in Documentation. Tooltip mode (see Tooltips) provides an example.
These text properties affect the behavior of the fill commands. They are used for representing formatted text. See Filling, and Margins.
harduse-hard-newlines minor mode is enabled. See Hard and Soft Newlines.
right-marginleft-marginjustificationSelf-inserting characters, the ones that get inserted into a buffer when the user types them (see Commands for Insertion), normally take on the same properties as the preceding character. This is called inheritance of properties.
By contrast, a Lisp program can do insertion with inheritance or without,
depending on the choice of insertion primitive. The ordinary text
insertion functions, such as insert, do not inherit any
properties. They insert text with precisely the properties of the
string being inserted, and no others. This is correct for programs
that copy text from one context to another—for example, into or out
of the kill ring. To insert with inheritance, use the special
primitives described in this section. Self-inserting characters
inherit properties because they work using these primitives.
When you do insertion with inheritance, which properties are inherited, and from where, depends on which properties are sticky. Insertion after a character inherits those of its properties that are rear-sticky. Insertion before a character inherits those of its properties that are front-sticky. When both sides offer different sticky values for the same property, the previous character's value takes precedence.
By default, a text property is rear-sticky but not front-sticky; thus, the default is to inherit all the properties of the preceding character, and nothing from the following character.
You can control the stickiness of various text properties with two
specific text properties, front-sticky and rear-nonsticky,
and with the variable text-property-default-nonsticky. You can
use the variable to specify a different default for a given property.
You can use those two text properties to make any specific properties
sticky or nonsticky in any particular part of the text.
If a character's front-sticky property is t, then all
its properties are front-sticky. If the front-sticky property is
a list, then the sticky properties of the character are those whose
names are in the list. For example, if a character has a
front-sticky property whose value is (face read-only),
then insertion before the character can inherit its face property
and its read-only property, but no others.
The rear-nonsticky property works the opposite way. Most
properties are rear-sticky by default, so the rear-nonsticky
property says which properties are not rear-sticky. If a
character's rear-nonsticky property is t, then none of its
properties are rear-sticky. If the rear-nonsticky property is a
list, properties are rear-sticky unless their names are in the
list.
This variable holds an alist which defines the default rear-stickiness of various text properties. Each element has the form
(property.nonstickiness), and it defines the stickiness of a particular text property, property.If nonstickiness is non-
nil, this means that the property property is rear-nonsticky by default. Since all properties are front-nonsticky by default, this makes property nonsticky in both directions by default.The text properties
front-stickyandrear-nonsticky, when used, take precedence over the default nonstickiness specified intext-property-default-nonsticky.
Here are the functions that insert text with inheritance of properties:
Insert the strings strings, just like the function
insert, but inherit any sticky properties from the adjoining text.
Insert the strings strings, just like the function
insert-before-markers, but inherit any sticky properties from the adjoining text.
See Insertion, for the ordinary insertion functions which do not inherit.
Instead of computing text properties for all the text in the buffer, you can arrange to compute the text properties for parts of the text when and if something depends on them.
The primitive that extracts text from the buffer along with its
properties is buffer-substring. Before examining the properties,
this function runs the abnormal hook buffer-access-fontify-functions.
This variable holds a list of functions for computing text properties. Before
buffer-substringcopies the text and text properties for a portion of the buffer, it calls all the functions in this list. Each of the functions receives two arguments that specify the range of the buffer being accessed. (The buffer itself is always the current buffer.)
The function buffer-substring-no-properties does not call these
functions, since it ignores text properties anyway.
In order to prevent the hook functions from being called more than
once for the same part of the buffer, you can use the variable
buffer-access-fontified-property.
If this variable's value is non-
nil, it is a symbol which is used as a text property name. A non-nilvalue for that text property means the other text properties for this character have already been computed.If all the characters in the range specified for
buffer-substringhave a non-nilvalue for this property,buffer-substringdoes not call thebuffer-access-fontify-functionsfunctions. It assumes these characters already have the right text properties, and just copies the properties they already have.The normal way to use this feature is that the
buffer-access-fontify-functionsfunctions add this property, as well as others, to the characters they operate on. That way, they avoid being called over and over for the same text.
Clickable text is text that can be clicked, with either the mouse or via a keyboard command, to produce some result. Many major modes use clickable text to implement textual hyper-links, or links for short.
The easiest way to insert and manipulate links is to use the
button package. See Buttons. In this section, we will
explain how to manually set up clickable text in a buffer, using text
properties. For simplicity, we will refer to the clickable text as a
link.
Implementing a link involves three separate steps: (1) indicating
clickability when the mouse moves over the link; (2) making <RET>
or mouse-2 on that link do something; and (3) setting up a
follow-link condition so that the link obeys
mouse-1-click-follows-link.
To indicate clickability, add the mouse-face text property to
the text of the link; then Emacs will highlight the link when the
mouse moves over it. In addition, you should define a tooltip or echo
area message, using the help-echo text property. See Special Properties. For instance, here is how Dired indicates that file
names are clickable:
(if (dired-move-to-filename)
(add-text-properties
(point)
(save-excursion
(dired-move-to-end-of-filename)
(point))
'(mouse-face highlight
help-echo "mouse-2: visit this file in other window")))
To make the link clickable, bind <RET> and mouse-2 to commands that perform the desired action. Each command should check to see whether it was called on a link, and act accordingly. For instance, Dired's major mode keymap binds mouse-2 to the following command:
(defun dired-mouse-find-file-other-window (event)
"In Dired, visit the file or directory name you click on."
(interactive "e")
(let ((window (posn-window (event-end event)))
(pos (posn-point (event-end event)))
file)
(if (not (windowp window))
(error "No file chosen"))
(with-current-buffer (window-buffer window)
(goto-char pos)
(setq file (dired-get-file-for-visit)))
(if (file-directory-p file)
(or (and (cdr dired-subdir-alist)
(dired-goto-subdir file))
(progn
(select-window window)
(dired-other-window file)))
(select-window window)
(find-file-other-window (file-name-sans-versions file t)))))
This command uses the functions posn-window and
posn-point to determine where the click occurred, and
dired-get-file-for-visit to determine which file to visit.
Instead of binding the mouse command in a major mode keymap, you can
bind it within the link text, using the keymap text property
(see Special Properties). For instance:
(let ((map (make-sparse-keymap)))
(define-key map [mouse-2] 'operate-this-button)
(put-text-property link-start link-end 'keymap map))
With this method, you can easily define different commands for different links. Furthermore, the global definition of <RET> and mouse-2 remain available for the rest of the text in the buffer.
The basic Emacs command for clicking on links is mouse-2.
However, for compatibility with other graphical applications, Emacs
also recognizes mouse-1 clicks on links, provided the user
clicks on the link quickly without moving the mouse. This behavior is
controlled by the user option mouse-1-click-follows-link.
See Mouse References.
To set up the link so that it obeys
mouse-1-click-follows-link, you must either (1) apply a
follow-link text or overlay property to the link text, or (2)
bind the follow-link event to a keymap (which can be a major
mode keymap or a local keymap specified via the keymap text
property). The value of the follow-link property, or the
binding for the follow-link event, acts as a condition for
the link action. This condition tells Emacs two things: the
circumstances under which a mouse-1 click should be regarded as
occurring inside the link, and how to compute an action code
that says what to translate the mouse-1 click into. The link
action condition can be one of the following:
mouse-facemouse-face, a position is inside
a link if there is a non-nil mouse-face property at that
position. The action code is always t.
For example, here is how Info mode handles <mouse-1>:
(define-key Info-mode-map [follow-link] 'mouse-face)
(func pos) evaluates to
non-nil. The value returned by func serves as the action
code.
For example, here is how pcvs enables mouse-1 to follow links on file names only:
(define-key map [follow-link]
(lambda (pos)
(eq (get-char-property pos 'face) 'cvs-filename-face)))
The action code tells mouse-1 how to follow the link:
"foo",
mouse-1 translates into f. If it is [foo],
mouse-1 translates into <foo>.
nil action code, the mouse-1 event is
translated into a mouse-2 event at the same position.
To define mouse-1 to activate a button defined with
define-button-type, give the button a follow-link
property. The property value should be a link action condition, as
described above. See Buttons. For example, here is how Help mode
handles mouse-1:
(define-button-type 'help-xref
'follow-link t
'action #'help-button-action)
To define mouse-1 on a widget defined with
define-widget, give the widget a :follow-link property.
The property value should be a link action condition, as described
above. For example, here is how the link widget specifies that
a <mouse-1> click shall be translated to <RET>:
(define-widget 'link 'item
"An embedded link."
:button-prefix 'widget-link-prefix
:button-suffix 'widget-link-suffix
:follow-link "\C-m"
:help-echo "Follow the link."
:format "%[%t%]")
This function returns non-
nilif position pos in the current buffer is on a link. pos can also be a mouse event location, as returned byevent-start(see Accessing Mouse).
A field is a range of consecutive characters in the buffer that are
identified by having the same value (comparing with eq) of the
field property (either a text-property or an overlay property).
This section describes special functions that are available for
operating on fields.
You specify a field with a buffer position, pos. We think of each field as containing a range of buffer positions, so the position you specify stands for the field containing that position.
When the characters before and after pos are part of the same
field, there is no doubt which field contains pos: the one those
characters both belong to. When pos is at a boundary between
fields, which field it belongs to depends on the stickiness of the
field properties of the two surrounding characters (see Sticky Properties). The field whose property would be inherited by text
inserted at pos is the field that contains pos.
There is an anomalous case where newly inserted text at pos
would not inherit the field property from either side. This
happens if the previous character's field property is not
rear-sticky, and the following character's field property is not
front-sticky. In this case, pos belongs to neither the preceding
field nor the following field; the field functions treat it as belonging
to an empty field whose beginning and end are both at pos.
In all of these functions, if pos is omitted or nil, the
value of point is used by default. If narrowing is in effect, then
pos should fall within the accessible portion. See Narrowing.
This function returns the beginning of the field specified by pos.
If pos is at the beginning of its field, and escape-from-edge is non-
nil, then the return value is always the beginning of the preceding field that ends at pos, regardless of the stickiness of thefieldproperties around pos.If limit is non-
nil, it is a buffer position; if the beginning of the field is before limit, then limit will be returned instead.
This function returns the end of the field specified by pos.
If pos is at the end of its field, and escape-from-edge is non-
nil, then the return value is always the end of the following field that begins at pos, regardless of the stickiness of thefieldproperties around pos.If limit is non-
nil, it is a buffer position; if the end of the field is after limit, then limit will be returned instead.
This function returns the contents of the field specified by pos, as a string.
This function returns the contents of the field specified by pos, as a string, discarding text properties.
This function deletes the text of the field specified by pos.
This function constrains new-pos to the field that old-pos belongs to—in other words, it returns the position closest to new-pos that is in the same field as old-pos.
If new-pos is
nil, thenconstrain-to-fielduses the value of point instead, and moves point to the resulting position in addition to returning that position.If old-pos is at the boundary of two fields, then the acceptable final positions depend on the argument escape-from-edge. If escape-from-edge is
nil, then new-pos must be in the field whosefieldproperty equals what new characters inserted at old-pos would inherit. (This depends on the stickiness of thefieldproperty for the characters before and after old-pos.) If escape-from-edge is non-nil, new-pos can be anywhere in the two adjacent fields. Additionally, if two fields are separated by another field with the special valueboundary, then any point within this special field is also considered to be on the boundary.Commands like C-a with no argument, that normally move backward to a specific kind of location and stay there once there, probably should specify
nilfor escape-from-edge. Other motion commands that check fields should probably passt.If the optional argument only-in-line is non-
nil, and constraining new-pos in the usual way would move it to a different line, new-pos is returned unconstrained. This used in commands that move by line, such asnext-lineandbeginning-of-line, so that they respect field boundaries only in the case where they can still move to the right line.If the optional argument inhibit-capture-property is non-
nil, and old-pos has a non-nilproperty of that name, then any field boundaries are ignored.You can cause
constrain-to-fieldto ignore all field boundaries (and so never constrain anything) by binding the variableinhibit-field-text-motionto a non-nilvalue.
Some editors that support adding attributes to text in the buffer do so by letting the user specify intervals within the text, and adding the properties to the intervals. Those editors permit the user or the programmer to determine where individual intervals start and end. We deliberately provided a different sort of interface in Emacs Lisp to avoid certain paradoxical behavior associated with text modification.
If the actual subdivision into intervals is meaningful, that means you can distinguish between a buffer that is just one interval with a certain property, and a buffer containing the same text subdivided into two intervals, both of which have that property.
Suppose you take the buffer with just one interval and kill part of the text. The text remaining in the buffer is one interval, and the copy in the kill ring (and the undo list) becomes a separate interval. Then if you yank back the killed text, you get two intervals with the same properties. Thus, editing does not preserve the distinction between one interval and two.
Suppose we attempt to fix this problem by coalescing the two intervals when the text is inserted. That works fine if the buffer originally was a single interval. But suppose instead that we have two adjacent intervals with the same properties, and we kill the text of one interval and yank it back. The same interval-coalescence feature that rescues the other case causes trouble in this one: after yanking, we have just one interval. Once again, editing does not preserve the distinction between one interval and two.
Insertion of text at the border between intervals also raises questions that have no satisfactory answer.
However, it is easy to arrange for editing to behave consistently for questions of the form, “What are the properties of text at this buffer or string position?” So we have decided these are the only questions that make sense; we have not implemented asking questions about where intervals start or end.
In practice, you can usually use the text property search functions in place of explicit interval boundaries. You can think of them as finding the boundaries of intervals, assuming that intervals are always coalesced whenever possible. See Property Search.
Emacs also provides explicit intervals as a presentation feature; see Overlays.
The following functions replace characters within a specified region based on their character codes.
This function replaces all occurrences of the character old-char with the character new-char in the region of the current buffer defined by start and end.
If noundo is non-
nil, thensubst-char-in-regiondoes not record the change for undo and does not mark the buffer as modified. This was useful for controlling the old selective display feature (see Selective Display).
subst-char-in-regiondoes not move point and returnsnil.---------- Buffer: foo ---------- This is the contents of the buffer before. ---------- Buffer: foo ---------- (subst-char-in-region 1 20 ?i ?X) => nil ---------- Buffer: foo ---------- ThXs Xs the contents of the buffer before. ---------- Buffer: foo ----------
This function applies a translation table to the characters in the buffer between positions start and end.
The translation table table is a string or a char-table;
(areftable ochar)gives the translated character corresponding to ochar. If table is a string, any characters with codes larger than the length of table are not altered by the translation.The return value of
translate-regionis the number of characters that were actually changed by the translation. This does not count characters that were mapped into themselves in the translation table.
A register is a sort of variable used in Emacs editing that can hold a variety of different kinds of values. Each register is named by a single character. All ASCII characters and their meta variants (but with the exception of C-g) can be used to name registers. Thus, there are 255 possible registers. A register is designated in Emacs Lisp by the character that is its name.
This variable is an alist of elements of the form
(name.contents). Normally, there is one element for each Emacs register that has been used.The object name is a character (an integer) identifying the register.
The contents of a register can have several possible types:
insert-register finds a number
in the register, it converts the number to decimal.
(window-configuration position)
(frame-configuration position)
The functions in this section return unpredictable values unless otherwise stated.
This function returns the contents of the register reg, or
nilif it has no contents.
This function sets the contents of register reg to value. A register can be set to any value, but the other register functions expect only certain data types. The return value is value.
This command inserts contents of register reg into the current buffer.
Normally, this command puts point before the inserted text, and the mark after it. However, if the optional second argument beforep is non-
nil, it puts the mark before and point after.When called interactively, the command defaults to putting point after text, and a prefix argument inverts this behavior.
If the register contains a rectangle, then the rectangle is inserted with its upper left corner at point. This means that text is inserted in the current line and underneath it on successive lines.
If the register contains something other than saved text (a string) or a rectangle (a list), currently useless things happen. This may be changed in the future.
This function reads and returns a register name, prompting with prompt and possibly showing a preview of the existing registers and their contents. The preview is shown in a temporary window, after the delay specified by the user option
register-preview-delay, if its value andregister-alistare both non-nil. The preview is also shown if the user requests help (e.g., by typing the help character). We recommend that all interactive commands which read register names use this function.
This function can be used to transpose stretches of text:
This function exchanges two nonoverlapping portions of the buffer. Arguments start1 and end1 specify the bounds of one portion and arguments start2 and end2 specify the bounds of the other portion.
Normally,
transpose-regionsrelocates markers with the transposed text; a marker previously positioned within one of the two transposed portions moves along with that portion, thus remaining between the same two characters in their new position. However, if leave-markers is non-nil,transpose-regionsdoes not do this—it leaves all markers unrelocated.
When auto-compression-mode is enabled, Emacs automatically
uncompresses compressed files when you visit them, and automatically
recompresses them if you alter and save them. See Compressed Files.
The above feature works by calling an external executable (e.g., gzip). Emacs can also be compiled with support for built-in decompression using the zlib library, which is faster than calling an external program.
This function returns non-
nilif built-in zlib decompression is available.
This function decompresses the region between start and end, using built-in zlib decompression. The region should contain data that were compressed with gzip or zlib. On success, the function replaces the contents of the region with the decompressed data. On failure, the function leaves the region unchanged and returns
nil. This function can be called only in unibyte buffers.
Base 64 code is used in email to encode a sequence of 8-bit bytes as a longer sequence of ASCII graphic characters. It is defined in Internet RFC142045. This section describes the functions for converting to and from this code.
This function converts the region from beg to end into base 64 code. It returns the length of the encoded text. An error is signaled if a character in the region is multibyte, i.e., in a multibyte buffer the region must contain only characters from the charsets
ascii,eight-bit-controlandeight-bit-graphic.Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument no-line-break is non-
nil, these newlines are not added, so the output is just one long line.
This function converts the string string into base 64 code. It returns a string containing the encoded text. As for
base64-encode-region, an error is signaled if a character in the string is multibyte.Normally, this function inserts newline characters into the encoded text, to avoid overlong lines. However, if the optional argument no-line-break is non-
nil, these newlines are not added, so the result string is just one long line.
This function converts the region from beg to end from base 64 code into the corresponding decoded text. It returns the length of the decoded text.
The decoding functions ignore newline characters in the encoded text.
This function converts the string string from base 64 code into the corresponding decoded text. It returns a unibyte string containing the decoded text.
The decoding functions ignore newline characters in the encoded text.
Emacs has built-in support for computing cryptographic hashes. A cryptographic hash, or checksum, is a digital fingerprint of a piece of data (e.g., a block of text) which can be used to check that you have an unaltered copy of that data.
Emacs supports several common cryptographic hash algorithms: MD5, SHA-1, SHA-2, SHA-224, SHA-256, SHA-384 and SHA-512. MD5 is the oldest of these algorithms, and is commonly used in message digests to check the integrity of messages transmitted over a network. MD5 is not collision resistant (i.e., it is possible to deliberately design different pieces of data which have the same MD5 hash), so you should not used it for anything security-related. A similar theoretical weakness also exists in SHA-1. Therefore, for security-related applications you should use the other hash types, such as SHA-2.
This function returns a hash for object. The argument algorithm is a symbol stating which hash to compute: one of
md5,sha1,sha224,sha256,sha384orsha512. The argument object should be a buffer or a string.The optional arguments start and end are character positions specifying the portion of object to compute the message digest for. If they are
nilor omitted, the hash is computed for the whole of object.If the argument binary is omitted or
nil, the function returns the text form of the hash, as an ordinary Lisp string. If binary is non-nil, it returns the hash in binary form, as a sequence of bytes stored in a unibyte string.This function does not compute the hash directly from the internal representation of object's text (see Text Representations). Instead, it encodes the text using a coding system (see Coding Systems), and computes the hash from that encoded text. If object is a buffer, the coding system used is the one which would be chosen by default for writing the text into a file. If object is a string, the user's preferred coding system is used (see Recognize Coding).
This function returns an MD5 hash. It is semi-obsolete, since for most purposes it is equivalent to calling
secure-hashwithmd5as the algorithm argument. The object, start and end arguments have the same meanings as insecure-hash.If coding-system is non-
nil, it specifies a coding system to use to encode the text; if omitted ornil, the default coding system is used, like insecure-hash.Normally,
md5signals an error if the text can't be encoded using the specified or chosen coding system. However, if noerror is non-nil, it silently usesraw-textcoding instead.
When Emacs is compiled with libxml2 support, the following functions are available to parse HTML or XML text into Lisp object trees.
This function parses the text between start and end as HTML, and returns a list representing the HTML parse tree. It attempts to handle real-world HTML by robustly coping with syntax mistakes.
The optional argument base-url, if non-
nil, should be a string specifying the base URL for relative URLs occurring in links.If the optional argument discard-comments is non-
nil, then the parse tree is created without any comments.In the parse tree, each HTML node is represented by a list in which the first element is a symbol representing the node name, the second element is an alist of node attributes, and the remaining elements are the subnodes.
The following example demonstrates this. Given this (malformed) HTML document:
<html><head></head><body width=101><div class=thing>Foo<div>YesA call to
libxml-parse-html-regionreturns this DOM (document object model):(html nil (head nil) (body ((width . "101")) (div ((class . "thing")) "Foo" (div nil "Yes"))))
This function renders the parsed HTML in dom into the current buffer. The argument dom should be a list as generated by
libxml-parse-html-region. This function is, e.g., used by EWW.
This function is the same as
libxml-parse-html-region, except that it parses the text as XML rather than HTML (so it is stricter about syntax).
The DOM returned by libxml-parse-html-region (and the
other XML parsing functions) is a tree structure where each
node has a node name (called a tag), and optional key/value
attribute list, and then a list of child nodes. The child
nodes are either strings or DOM objects.
(body ((width . "101"))
(div ((class . "thing"))
"Foo"
(div nil
"Yes")))
This function creates a DOM node of type tag. If given, attributes should be a key/value pair list. If given, children should be DOM nodes.
The following functions can be used to work with this structure. Each function takes a DOM node, or a list of nodes. In the latter case, only the first node in the list is used.
Simple accessors:
dom-tag node
dom-attr node attribute
(dom-attr img 'href)
=> "http://fsf.org/logo.png"
dom-children node
dom-non-text-children node
dom-attributes node
dom-text node
dom-texts node
dom-parent dom node
The following are functions for altering the DOM.
dom-set-attribute node attribute value
dom-append-child node child
dom-add-child-before node child before
nil, make child the first child.
dom-set-attributes node attributes
The following are functions for searching for elements in the DOM. They all return lists of matching nodes.
dom-by-tag dom tag
(dom-by-tag dom 'td)
=> '((td ...) (td ...) (td ...))
dom-by-class dom match
dom-by-style dom style
dom-by-id dom style
dom-strings dom
Utility functions:
dom-pp dom &optional remove-empty
In database terminology, an atomic change is an indivisible change—it can succeed entirely or it can fail entirely, but it cannot partly succeed. A Lisp program can make a series of changes to one or several buffers as an atomic change group, meaning that either the entire series of changes will be installed in their buffers or, in case of an error, none of them will be.
To do this for one buffer, the one already current, simply write a
call to atomic-change-group around the code that makes the
changes, like this:
(atomic-change-group
(insert foo)
(delete-region x y))
If an error (or other nonlocal exit) occurs inside the body of
atomic-change-group, it unmakes all the changes in that buffer
that were during the execution of the body. This kind of change group
has no effect on any other buffers—any such changes remain.
If you need something more sophisticated, such as to make changes in
various buffers constitute one atomic group, you must directly call
lower-level functions that atomic-change-group uses.
This function sets up a change group for buffer buffer, which defaults to the current buffer. It returns a handle that represents the change group. You must use this handle to activate the change group and subsequently to finish it.
To use the change group, you must activate it. You must do this before making any changes in the text of buffer.
This function activates the change group that handle designates.
After you activate the change group, any changes you make in that buffer become part of it. Once you have made all the desired changes in the buffer, you must finish the change group. There are two ways to do this: you can either accept (and finalize) all the changes, or cancel them all.
This function accepts all the changes in the change group specified by handle, making them final.
This function cancels and undoes all the changes in the change group specified by handle.
Your code should use unwind-protect to make sure the group is
always finished. The call to activate-change-group should be
inside the unwind-protect, in case the user types C-g
just after it runs. (This is one reason why
prepare-change-group and activate-change-group are
separate functions, because normally you would call
prepare-change-group before the start of that
unwind-protect.) Once you finish the group, don't use the
handle again—in particular, don't try to finish the same group
twice.
To make a multibuffer change group, call prepare-change-group
once for each buffer you want to cover, then use nconc to
combine the returned values, like this:
(nconc (prepare-change-group buffer-1)
(prepare-change-group buffer-2))
You can then activate the multibuffer change group with a single call
to activate-change-group, and finish it with a single call to
accept-change-group or cancel-change-group.
Nested use of several change groups for the same buffer works as you would expect. Non-nested use of change groups for the same buffer will get Emacs confused, so don't let it happen; the first change group you start for any given buffer should be the last one finished.
These hook variables let you arrange to take notice of all changes in all buffers (or in a particular buffer, if you make them buffer-local). See also Special Properties, for how to detect changes to specific parts of the text.
The functions you use in these hooks should save and restore the match data if they do anything that uses regular expressions; otherwise, they will interfere in bizarre ways with the editing operations that call them.
This variable holds a list of functions to call before any buffer modification. Each function gets two arguments, the beginning and end of the region that is about to change, represented as integers. The buffer that is about to change is always the current buffer.
This variable holds a list of functions to call after any buffer modification. Each function receives three arguments: the beginning and end of the region just changed, and the length of the text that existed before the change. All three arguments are integers. The buffer that has been changed is always the current buffer.
The length of the old text is the difference between the buffer positions before and after that text as it was before the change. As for the changed text, its length is simply the difference between the first two arguments.
Output of messages into the *Messages* buffer does not call these functions.
The macro executes body normally, but arranges to call the after-change functions just once for a series of several changes—if that seems safe.
If a program makes several text changes in the same area of the buffer, using the macro
combine-after-change-callsaround that part of the program can make it run considerably faster when after-change hooks are in use. When the after-change hooks are ultimately called, the arguments specify a portion of the buffer including all of the changes made within thecombine-after-change-callsbody.Warning: You must not alter the values of
after-change-functionswithin the body of acombine-after-change-callsform.Warning: if the changes you combine occur in widely scattered parts of the buffer, this will still work, but it is not advisable, because it may lead to inefficient behavior for some change hook functions.
This variable is a normal hook that is run whenever a buffer is changed that was previously in the unmodified state.
If this variable is non-
nil, all of the change hooks are disabled; none of them run. This affects all the hook variables described above in this section, as well as the hooks attached to certain special text properties (see Special Properties) and overlay properties (see Overlay Properties).Also, this variable is bound to non-
nilwhile running those same hook variables, so that by default modifying the buffer from a modification hook does not cause other modification hooks to be run. If you do want modification hooks to be run in a particular piece of code that is itself run from a modification hook, then rebind locallyinhibit-modification-hookstonil.
This chapter covers the special issues relating to characters and how they are stored in strings and buffers.
Emacs buffers and strings support a large repertoire of characters from many different scripts, allowing users to type and display text in almost any known written language.
To support this multitude of characters and scripts, Emacs closely
follows the Unicode Standard. The Unicode Standard assigns a
unique number, called a codepoint, to each and every character.
The range of codepoints defined by Unicode, or the Unicode
codespace, is 0..#x10FFFF (in hexadecimal notation),
inclusive. Emacs extends this range with codepoints in the range
#x110000..#x3FFFFF, which it uses for representing characters
that are not unified with Unicode and raw 8-bit bytes that
cannot be interpreted as characters. Thus, a character codepoint in
Emacs is a 22-bit integer.
To conserve memory, Emacs does not hold fixed-length 22-bit numbers that are codepoints of text characters within buffers and strings. Rather, Emacs uses a variable-length internal representation of characters, that stores each character as a sequence of 1 to 5 8-bit bytes, depending on the magnitude of its codepoint15. For example, any ASCII character takes up only 1 byte, a Latin-1 character takes up 2 bytes, etc. We call this representation of text multibyte.
Outside Emacs, characters can be represented in many different encodings, such as ISO-8859-1, GB-2312, Big-5, etc. Emacs converts between these external encodings and its internal representation, as appropriate, when it reads text into a buffer or a string, or when it writes text to a disk file or passes it to some other process.
Occasionally, Emacs needs to hold and manipulate encoded text or binary non-text data in its buffers or strings. For example, when Emacs visits a file, it first reads the file's text verbatim into a buffer, and only then converts it to the internal representation. Before the conversion, the buffer holds encoded text.
Encoded text is not really text, as far as Emacs is concerned, but
rather a sequence of raw 8-bit bytes. We call buffers and strings
that hold encoded text unibyte buffers and strings, because
Emacs treats them as a sequence of individual bytes. Usually, Emacs
displays unibyte buffers and strings as octal codes such as
\237. We recommend that you never use unibyte buffers and
strings except for manipulating encoded text or binary non-text data.
In a buffer, the buffer-local value of the variable
enable-multibyte-characters specifies the representation used.
The representation for a string is determined and recorded in the string
when the string is constructed.
This variable specifies the current buffer's text representation. If it is non-
nil, the buffer contains multibyte text; otherwise, it contains unibyte encoded text or binary non-text data.You cannot set this variable directly; instead, use the function
set-buffer-multibyteto change a buffer's representation.
Buffer positions are measured in character units. This function returns the byte-position corresponding to buffer position position in the current buffer. This is 1 at the start of the buffer, and counts upward in bytes. If position is out of range, the value is
nil.
Return the buffer position, in character units, corresponding to given byte-position in the current buffer. If byte-position is out of range, the value is
nil. In a multibyte buffer, an arbitrary value of byte-position can be not at character boundary, but inside a multibyte sequence representing a single character; in this case, this function returns the buffer position of the character whose multibyte sequence includes byte-position. In other words, the value does not change for all byte positions that belong to the same character.
The following two functions are useful when a Lisp program needs to map buffer positions to byte offsets in a file visited by the buffer.
This function is similar to
position-bytes, but instead of byte position in the current buffer it returns the offset from the beginning of the current buffer's file of the byte that corresponds to the given character position in the buffer. The conversion requires to know how the text is encoded in the buffer's file; this is what the coding-system argument is for, defaulting to the value ofbuffer-file-coding-system. The optional argument quality specifies how accurate the result should be; it should be one of the following:
exact- The result must be accurate. The function may need to encode and decode a large part of the buffer.
approximate- The value can be an approximation. The function may avoid expensive processing and return an inexact result.
nil- If the exact result needs expensive processing, the function will return
nilrather than an approximation. This is the default if the argument is omitted.
This function returns the buffer position corresponding to a file position specified by byte, a zero-base byte offset from the file's beginning. The function performs the conversion opposite to what
bufferpos-to-fileposdoes. Optional arguments quality and coding-system have the same meaning and values as forbufferpos-to-filepos.
Return
tif string is a multibyte string,nilotherwise. This function also returnsnilif string is some object other than a string.
This function returns the number of bytes in string. If string is a multibyte string, this can be greater than
(lengthstring).
This function concatenates all its argument bytes and makes the result a unibyte string.
By default, Emacs starts in multibyte mode: it stores the contents of buffers and strings using an internal encoding that represents non-ASCII characters using multi-byte sequences. Multibyte mode allows you to use all the supported languages and scripts without limitations.
Under very special circumstances, you may want to disable multibyte character support, for a specific buffer. When multibyte characters are disabled in a buffer, we call that unibyte mode. In unibyte mode, each character in the buffer has a character code ranging from 0 through 255 (0377 octal); 0 through 127 (0177 octal) represent ASCII characters, and 128 (0200 octal) through 255 (0377 octal) represent non-ASCII characters.
To edit a particular file in unibyte representation, visit it using
find-file-literally. See Visiting Functions. You can
convert a multibyte buffer to unibyte by saving it to a file, killing
the buffer, and visiting the file again with
find-file-literally. Alternatively, you can use C-x
<RET> c (universal-coding-system-argument) and specify
`raw-text' as the coding system with which to visit or save a
file. See Specifying a Coding System for File Text. Unlike find-file-literally, finding
a file as `raw-text' doesn't disable format conversion,
uncompression, or auto mode selection.
The buffer-local variable enable-multibyte-characters is
non-nil in multibyte buffers, and nil in unibyte ones.
The mode line also indicates whether a buffer is multibyte or not.
With a graphical display, in a multibyte buffer, the portion of the
mode line that indicates the character set has a tooltip that (amongst
other things) says that the buffer is multibyte. In a unibyte buffer,
the character set indicator is absent. Thus, in a unibyte buffer
(when using a graphical display) there is normally nothing before the
indication of the visited file's end-of-line convention (colon,
backslash, etc.), unless you are using an input method.
You can turn off multibyte support in a specific buffer by invoking the
command toggle-enable-multibyte-characters in that buffer.
Emacs can convert unibyte text to multibyte; it can also convert multibyte text to unibyte, provided that the multibyte text contains only ASCII and 8-bit raw bytes. In general, these conversions happen when inserting text into a buffer, or when putting text from several strings together in one string. You can also explicitly convert a string's contents to either representation.
Emacs chooses the representation for a string based on the text from which it is constructed. The general rule is to convert unibyte text to multibyte text when combining it with other multibyte text, because the multibyte representation is more general and can hold whatever characters the unibyte text has.
When inserting text into a buffer, Emacs converts the text to the
buffer's representation, as specified by
enable-multibyte-characters in that buffer. In particular, when
you insert multibyte text into a unibyte buffer, Emacs converts the text
to unibyte, even though this conversion cannot in general preserve all
the characters that might be in the multibyte text. The other natural
alternative, to convert the buffer contents to multibyte, is not
acceptable because the buffer's representation is a choice made by the
user that cannot be overridden automatically.
Converting unibyte text to multibyte text leaves ASCII characters unchanged, and converts bytes with codes 128 through 255 to the multibyte representation of raw eight-bit bytes.
Converting multibyte text to unibyte converts all ASCII and eight-bit characters to their single-byte form, but loses information for non-ASCII characters by discarding all but the low 8 bits of each character's codepoint. Converting unibyte text to multibyte and back to unibyte reproduces the original unibyte text.
The next two functions either return the argument string, or a newly created string with no text properties.
This function returns a multibyte string containing the same sequence of characters as string. If string is a multibyte string, it is returned unchanged. The function assumes that string includes only ASCII characters and raw 8-bit bytes; the latter are converted to their multibyte representation corresponding to the codepoints
#x3FFF80through#x3FFFFF, inclusive (see codepoints).
This function returns a unibyte string containing the same sequence of characters as string. It signals an error if string contains a non-ASCII character. If string is a unibyte string, it is returned unchanged. Use this function for string arguments that contain only ASCII and eight-bit characters.
This function returns a unibyte string containing a single byte of character data, character. It signals an error if character is not an integer between 0 and 255.
This converts the multibyte character char to a unibyte character, and returns that character. If char is neither ASCII nor eight-bit, the function returns −1.
This convert the unibyte character char to a multibyte character, assuming char is either ASCII or raw 8-bit byte.
Sometimes it is useful to examine an existing buffer or string as multibyte when it was unibyte, or vice versa.
Set the representation type of the current buffer. If multibyte is non-
nil, the buffer becomes multibyte. If multibyte isnil, the buffer becomes unibyte.This function leaves the buffer contents unchanged when viewed as a sequence of bytes. As a consequence, it can change the contents viewed as characters; for instance, a sequence of three bytes which is treated as one character in multibyte representation will count as three characters in unibyte representation. Eight-bit characters representing raw bytes are an exception. They are represented by one byte in a unibyte buffer, but when the buffer is set to multibyte, they are converted to two-byte sequences, and vice versa.
This function sets
enable-multibyte-charactersto record which representation is in use. It also adjusts various data in the buffer (including overlays, text properties and markers) so that they cover the same text as they did before.This function signals an error if the buffer is narrowed, since the narrowing might have occurred in the middle of multibyte character sequences.
This function also signals an error if the buffer is an indirect buffer. An indirect buffer always inherits the representation of its base buffer.
If string is already a unibyte string, this function returns string itself. Otherwise, it returns a new string with the same bytes as string, but treating each byte as a separate character (so that the value may have more characters than string); as an exception, each eight-bit character representing a raw byte is converted into a single byte. The newly-created string contains no text properties.
If string is a multibyte string, this function returns string itself. Otherwise, it returns a new string with the same bytes as string, but treating each multibyte sequence as one character. This means that the value may have fewer characters than string has. If a byte sequence in string is invalid as a multibyte representation of a single character, each byte in the sequence is treated as a raw 8-bit byte. The newly-created string contains no text properties.
The unibyte and multibyte text representations use different
character codes. The valid character codes for unibyte representation
range from 0 to #xFF (255)—the values that can fit in one
byte. The valid character codes for multibyte representation range
from 0 to #x3FFFFF. In this code space, values 0 through
#x7F (127) are for ASCII characters, and values
#x80 (128) through #x3FFF7F (4194175) are for
non-ASCII characters.
Emacs character codes are a superset of the Unicode standard.
Values 0 through #x10FFFF (1114111) correspond to Unicode
characters of the same codepoint; values #x110000 (1114112)
through #x3FFF7F (4194175) represent characters that are not
unified with Unicode; and values #x3FFF80 (4194176) through
#x3FFFFF (4194303) represent eight-bit raw bytes.
This returns
tif charcode is a valid character, andnilotherwise.(characterp 65) => t (characterp 4194303) => t (characterp 4194304) => nil
This function returns the largest value that a valid character codepoint can have.
(characterp (max-char)) => t (characterp (1+ (max-char))) => nil
This function returns the byte at character position pos in the current buffer. If the current buffer is unibyte, this is literally the byte at that position. If the buffer is multibyte, byte values of ASCII characters are the same as character codepoints, whereas eight-bit raw bytes are converted to their 8-bit codes. The function signals an error if the character at pos is non-ASCII.
The optional argument string means to get a byte value from that string instead of the current buffer.
A character property is a named attribute of a character that specifies how the character behaves and how it should be handled during text processing and display. Thus, character properties are an important part of specifying the character's semantics.
On the whole, Emacs follows the Unicode Standard in its implementation of character properties. In particular, Emacs supports the Unicode Character Property Model, and the Emacs character property database is derived from the Unicode Character Database (UCD). See the Character Properties chapter of the Unicode Standard, for a detailed description of Unicode character properties and their meaning. This section assumes you are already familiar with that chapter of the Unicode Standard, and want to apply that knowledge to Emacs Lisp programs.
In Emacs, each property has a name, which is a symbol, and a set of
possible values, whose types depend on the property; if a character
does not have a certain property, the value is nil. As a
general rule, the names of character properties in Emacs are produced
from the corresponding Unicode properties by downcasing them and
replacing each `_' character with a dash `-'. For example,
Canonical_Combining_Class becomes
canonical-combining-class. However, sometimes we shorten the
names to make their use easier.
Some codepoints are left unassigned by the UCD—they don't correspond to any character. The Unicode Standard defines default values of properties for such codepoints; they are mentioned below for each property.
Here is the full list of value types for all the character properties that Emacs knows about:
nameName Unicode property. The value is a
string consisting of upper-case Latin letters A to Z, digits, spaces,
and hyphen `-' characters. For unassigned codepoints, the value
is nil.
general-categoryGeneral_Category Unicode property. The
value is a symbol whose name is a 2-letter abbreviation of the
character's classification. For unassigned codepoints, the value
is Cn.
canonical-combining-classCanonical_Combining_Class Unicode property.
The value is an integer. For unassigned codepoints, the value
is zero.
bidi-classBidi_Class property. The value is a
symbol whose name is the Unicode directional type of the
character. Emacs uses this property when it reorders bidirectional
text for display (see Bidirectional Display). For unassigned
codepoints, the value depends on the code blocks to which the
codepoint belongs: most unassigned codepoints get the value of
L (strong L), but some get values of AL (Arabic letter)
or R (strong R).
decompositionDecomposition_Type and
Decomposition_Value. The value is a list, whose first element
may be a symbol representing a compatibility formatting tag, such as
small16; the other elements are characters that give the
compatibility decomposition sequence of this character. For
characters that don't have decomposition sequences, and for unassigned
codepoints, the value is a list with a single member, the character
itself.
decimal-digit-valueNumeric_Value property for
characters whose Numeric_Type is `Decimal'. The value is
an integer, or nil if the character has no decimal digit value.
For unassigned codepoints, the value is nil, which means
NaN, or “not a number”.
digit-valueNumeric_Value property for
characters whose Numeric_Type is `Digit'. The value is an
integer. Examples of such characters include compatibility subscript
and superscript digits, for which the value is the corresponding
number. For characters that don't have any numeric value, and for
unassigned codepoints, the value is nil, which means
NaN.
numeric-valueNumeric_Value property for
characters whose Numeric_Type is `Numeric'. The value of
this property is a number. Examples of characters that have this
property include fractions, subscripts, superscripts, Roman numerals,
currency numerators, and encircled numbers. For example, the value of
this property for the character U+2155 (vulgar fraction one
fifth) is 0.2. For characters that don't have any numeric
value, and for unassigned codepoints, the value is nil, which
means NaN.
mirroredBidi_Mirrored property. The value
of this property is a symbol, either Y or N. For
unassigned codepoints, the value is N.
mirroringBidi_Mirroring_Glyph property. The
value of this property is a character whose glyph represents the
mirror image of the character's glyph, or nil if there's no
defined mirroring glyph. All the characters whose mirrored
property is N have nil as their mirroring
property; however, some characters whose mirrored property is
Y also have nil for mirroring, because no
appropriate characters exist with mirrored glyphs. Emacs uses this
property to display mirror images of characters when appropriate
(see Bidirectional Display). For unassigned codepoints, the value
is nil.
paired-bracketBidi_Paired_Bracket property. The
value of this property is the codepoint of a character's paired
bracket, or nil if the character is not a bracket character.
This establishes a mapping between characters that are treated as
bracket pairs by the Unicode Bidirectional Algorithm; Emacs uses this
property when it decides how to reorder for display parentheses,
braces, and other similar characters (see Bidirectional Display).
bracket-typeBidi_Paired_Bracket_Type property.
For characters whose paired-bracket property is non-nil,
the value of this property is a symbol, either o (for opening
bracket characters) or c (for closing bracket characters). For
characters whose paired-bracket property is nil, the
value is the symbol n (None). Like paired-bracket, this
property is used for bidirectional display.
old-nameUnicode_1_Name property. The value
is a string. For unassigned codepoints, and characters that have no
value for this property, the value is nil.
iso-10646-commentISO_Comment property. The value is
either a string or nil. For unassigned codepoints, the value
is nil.
uppercaseSimple_Uppercase_Mapping property.
The value of this property is a single character. For unassigned
codepoints, the value is nil, which means the character itself.
lowercaseSimple_Lowercase_Mapping property.
The value of this property is a single character. For unassigned
codepoints, the value is nil, which means the character itself.
titlecaseSimple_Titlecase_Mapping property.
Title case is a special form of a character used when the first
character of a word needs to be capitalized. The value of this
property is a single character. For unassigned codepoints, the value
is nil, which means the character itself.
This function returns the value of char's propname property.
(get-char-code-property ?\s 'general-category) => Zs (get-char-code-property ?1 'general-category) => Nd ;; U+2084 SUBSCRIPT FOUR (get-char-code-property ?\u2084 'digit-value) => 4 ;; U+2155 VULGAR FRACTION ONE FIFTH (get-char-code-property ?\u2155 'numeric-value) => 0.2 ;; U+2163 ROMAN NUMERAL FOUR (get-char-code-property ?\u2163 'numeric-value) => 4 (get-char-code-property ?\( 'paired-bracket) => 41 ;; closing parenthesis (get-char-code-property ?\) 'bracket-type) => c
This function returns the description string of property prop's value, or
nilif value has no description.(char-code-property-description 'general-category 'Zs) => "Separator, Space" (char-code-property-description 'general-category 'Nd) => "Number, Decimal Digit" (char-code-property-description 'numeric-value '1/5) => nil
This function stores value as the value of the property propname for the character char.
The value of this variable is a char-table (see Char-Tables) that specifies, for each character, its Unicode
General_Categoryproperty as a symbol.
The value of this variable is a char-table that specifies, for each character, a symbol whose name is the script to which the character belongs, according to the Unicode Standard classification of the Unicode code space into script-specific blocks. This char-table has a single extra slot whose value is the list of all script symbols.
The value of this variable is a char-table that specifies the width of each character in columns that it will occupy on the screen.
The value of this variable is a char-table that specifies, for each character, whether it is printable or not. That is, if evaluating
(aref printable-chars char)results int, the character is printable, and if it results innil, it is not.
An Emacs character set, or charset, is a set of characters
in which each character is assigned a numeric code point. (The
Unicode Standard calls this a coded character set.) Each Emacs
charset has a name which is a symbol. A single character can belong
to any number of different character sets, but it will generally have
a different code point in each charset. Examples of character sets
include ascii, iso-8859-1, greek-iso8859-7, and
windows-1255. The code point assigned to a character in a
charset is usually different from its code point used in Emacs buffers
and strings.
Emacs defines several special character sets. The character set
unicode includes all the characters whose Emacs code points are
in the range 0..#x10FFFF. The character set emacs
includes all ASCII and non-ASCII characters.
Finally, the eight-bit charset includes the 8-bit raw bytes;
Emacs uses it to represent raw bytes encountered in text.
Returns
tif object is a symbol that names a character set,nilotherwise.
This function returns a list of all defined character sets ordered by their priority. If highestp is non-
nil, the function returns a single character set of the highest priority.
This function makes charsets the highest priority character sets.
This function returns the name of the character set of highest priority that character belongs to. ASCII characters are an exception: for them, this function always returns
ascii.If restriction is non-
nil, it should be a list of charsets to search. Alternatively, it can be a coding system, in which case the returned charset must be supported by that coding system (see Coding Systems).
This function returns the property list of the character set charset. Although charset is a symbol, this is not the same as the property list of that symbol. Charset properties include important information about the charset, such as its documentation string, short name, etc.
This function sets the propname property of charset to the given value.
This function returns the value of charsets property propname.
This command displays a list of characters in the character set charset.
Emacs can convert between its internal representation of a character and the character's codepoint in a specific charset. The following two functions support these conversions.
This function decodes a character that is assigned a code-point in charset, to the corresponding Emacs character, and returns it. If charset doesn't contain a character of that code point, the value is
nil. If code-point doesn't fit in a Lisp integer (see most-positive-fixnum), it can be specified as a cons cell(high.low), where low are the lower 16 bits of the value and high are the high 16 bits.
This function returns the code point assigned to the character char in charset. If the result does not fit in a Lisp integer, it is returned as a cons cell
(high.low)that fits the second argument ofdecode-charabove. If charset doesn't have a codepoint for char, the value isnil.
The following function comes in handy for applying a certain function to all or part of the characters in a charset:
Call function for characters in charset. function is called with two arguments. The first one is a cons cell
(from.to), where from and to indicate a range of characters contained in charset. The second argument passed to function is arg.By default, the range of codepoints passed to function includes all the characters in charset, but optional arguments from-code and to-code limit that to the range of characters between these two codepoints of charset. If either of them is
nil, it defaults to the first or last codepoint of charset, respectively.
Sometimes it is useful to find out which character set a particular character belongs to. One use for this is in determining which coding systems (see Coding Systems) are capable of representing all of the text in question; another is to determine the font(s) for displaying that text.
This function returns the charset of highest priority containing the character at position pos in the current buffer. If pos is omitted or
nil, it defaults to the current value of point. If pos is out of range, the value isnil.
This function returns a list of the character sets of highest priority that contain characters in the current buffer between positions beg and end.
The optional argument translation specifies a translation table to use for scanning the text (see Translation of Characters). If it is non-
nil, then each character in the region is translated through this table, and the value returned describes the translated characters instead of the characters actually in the buffer.
This function returns a list of character sets of highest priority that contain characters in string. It is just like
find-charset-region, except that it applies to the contents of string instead of part of the current buffer.
A translation table is a char-table (see Char-Tables) that specifies a mapping of characters into characters. These tables are used in encoding and decoding, and for other purposes. Some coding systems specify their own particular translation tables; there are also default translation tables which apply to all other coding systems.
A translation table has two extra slots. The first is either
nil or a translation table that performs the reverse
translation; the second is the maximum number of characters to look up
for translating sequences of characters (see the description of
make-translation-table-from-alist below).
This function returns a translation table based on the argument translations. Each element of translations should be a list of elements of the form
(from.to); this says to translate the character from into to.The arguments and the forms in each argument are processed in order, and if a previous form already translates to to some other character, say to-alt, from is also translated to to-alt.
During decoding, the translation table's translations are applied to
the characters that result from ordinary decoding. If a coding system
has the property :decode-translation-table, that specifies the
translation table to use, or a list of translation tables to apply in
sequence. (This is a property of the coding system, as returned by
coding-system-get, not a property of the symbol that is the
coding system's name. See Basic Concepts of Coding Systems.) Finally, if
standard-translation-table-for-decode is non-nil, the
resulting characters are translated by that table.
During encoding, the translation table's translations are applied to
the characters in the buffer, and the result of translation is
actually encoded. If a coding system has property
:encode-translation-table, that specifies the translation table
to use, or a list of translation tables to apply in sequence. In
addition, if the variable standard-translation-table-for-encode
is non-nil, it specifies the translation table to use for
translating the result.
This is the default translation table for decoding. If a coding systems specifies its own translation tables, the table that is the value of this variable, if non-
nil, is applied after them.
This is the default translation table for encoding. If a coding systems specifies its own translation tables, the table that is the value of this variable, if non-
nil, is applied after them.
Self-inserting characters are translated through this translation table before they are inserted. Search commands also translate their input through this table, so they can compare more reliably with what's in the buffer.
This variable automatically becomes buffer-local when set.
This function returns a translation table made from vec that is an array of 256 elements to map bytes (values 0 through #xFF) to characters. Elements may be
nilfor untranslated bytes. The returned table has a translation table for reverse mapping in the first extra slot, and the value1in the second extra slot.This function provides an easy way to make a private coding system that maps each byte to a specific character. You can specify the returned table and the reverse translation table using the properties
:decode-translation-tableand:encode-translation-tablerespectively in the props argument todefine-coding-system.
This function is similar to
make-translation-tablebut returns a complex translation table rather than a simple one-to-one mapping. Each element of alist is of the form(from.to), where from and to are either characters or vectors specifying a sequence of characters. If from is a character, that character is translated to to (i.e., to a character or a character sequence). If from is a vector of characters, that sequence is translated to to. The returned table has a translation table for reverse mapping in the first extra slot, and the maximum length of all the from character sequences in the second extra slot.
When Emacs reads or writes a file, and when Emacs sends text to a subprocess or receives text from a subprocess, it normally performs character code conversion and end-of-line conversion as specified by a particular coding system.
How to define a coding system is an arcane matter, and is not documented here.
Character code conversion involves conversion between the internal representation of characters used inside Emacs and some other encoding. Emacs supports many different encodings, in that it can convert to and from them. For example, it can convert text to or from encodings such as Latin 1, Latin 2, Latin 3, Latin 4, Latin 5, and several variants of ISO 2022. In some cases, Emacs supports several alternative encodings for the same characters; for example, there are three coding systems for the Cyrillic (Russian) alphabet: ISO, Alternativnyj, and KOI8.
Every coding system specifies a particular set of character code
conversions, but the coding system undecided is special: it
leaves the choice unspecified, to be chosen heuristically for each
file, based on the file's data.
In general, a coding system doesn't guarantee roundtrip identity: decoding a byte sequence using coding system, then encoding the resulting text in the same coding system, can produce a different byte sequence. But some coding systems do guarantee that the byte sequence will be the same as what you originally decoded. Here are a few examples:
iso-8859-1, utf-8, big5, shift_jis, euc-jp
Encoding buffer text and then decoding the result can also fail to reproduce the original text. For instance, if you encode a character with a coding system which does not support that character, the result is unpredictable, and thus decoding it using the same coding system may produce a different text. Currently, Emacs can't report errors that result from encoding unsupported characters.
End of line conversion handles three different conventions used on various systems for representing end of line in files. The Unix convention, used on GNU and Unix systems, is to use the linefeed character (also called newline). The DOS convention, used on MS-Windows and MS-DOS systems, is to use a carriage-return and a linefeed at the end of a line. The Mac convention is to use just carriage-return. (This was the convention used on the Macintosh system prior to OS X.)
Base coding systems such as latin-1 leave the end-of-line
conversion unspecified, to be chosen based on the data. Variant
coding systems such as latin-1-unix, latin-1-dos and
latin-1-mac specify the end-of-line conversion explicitly as
well. Most base coding systems have three corresponding variants whose
names are formed by adding `-unix', `-dos' and `-mac'.
The coding system raw-text is special in that it prevents
character code conversion, and causes the buffer visited with this
coding system to be a unibyte buffer. For historical reasons, you can
save both unibyte and multibyte text with this coding system. When
you use raw-text to encode multibyte text, it does perform one
character code conversion: it converts eight-bit characters to their
single-byte external representation. raw-text does not specify
the end-of-line conversion, allowing that to be determined as usual by
the data, and has the usual three variants which specify the
end-of-line conversion.
no-conversion (and its alias binary) is equivalent to
raw-text-unix: it specifies no conversion of either character
codes or end-of-line.
The coding system utf-8-emacs specifies that the data is
represented in the internal Emacs encoding (see Text Representations). This is like raw-text in that no code
conversion happens, but different in that the result is multibyte
data. The name emacs-internal is an alias for
utf-8-emacs.
This function returns the specified property of the coding system coding-system. Most coding system properties exist for internal purposes, but one that you might find useful is
:mime-charset. That property's value is the name used in MIME for the character coding which this coding system can read and write. Examples:(coding-system-get 'iso-latin-1 :mime-charset) => iso-8859-1 (coding-system-get 'iso-2022-cn :mime-charset) => iso-2022-cn (coding-system-get 'cyrillic-koi8 :mime-charset) => koi8-rThe value of the
:mime-charsetproperty is also defined as an alias for the coding system.
This function returns the list of aliases of coding-system.
The principal purpose of coding systems is for use in reading and
writing files. The function insert-file-contents uses a coding
system to decode the file data, and write-region uses one to
encode the buffer contents.
You can specify the coding system to use either explicitly
(see Specifying Coding Systems), or implicitly using a default
mechanism (see Default Coding Systems). But these methods may not
completely specify what to do. For example, they may choose a coding
system such as undefined which leaves the character code
conversion to be determined from the data. In these cases, the I/O
operation finishes the job of choosing a coding system. Very often
you will want to find out afterwards which coding system was chosen.
This buffer-local variable records the coding system used for saving the buffer and for writing part of the buffer with
write-region. If the text to be written cannot be safely encoded using the coding system specified by this variable, these operations select an alternative encoding by calling the functionselect-safe-coding-system(see User-Chosen Coding Systems). If selecting a different encoding requires to ask the user to specify a coding system,buffer-file-coding-systemis updated to the newly selected coding system.
buffer-file-coding-systemdoes not affect sending text to a subprocess.
This variable specifies the coding system for saving the buffer (by overriding
buffer-file-coding-system). Note that it is not used forwrite-region.When a command to save the buffer starts out to use
buffer-file-coding-system(orsave-buffer-coding-system), and that coding system cannot handle the actual text in the buffer, the command asks the user to choose another coding system (by callingselect-safe-coding-system). After that happens, the command also updatesbuffer-file-coding-systemto represent the coding system that the user specified.
I/O operations for files and subprocesses set this variable to the coding system name that was used. The explicit encoding and decoding functions (see Explicit Encoding) set it too.
Warning: Since receiving subprocess output sets this variable, it can change whenever Emacs waits; therefore, you should copy the value shortly after the function call that stores the value you are interested in.
The variable selection-coding-system specifies how to encode
selections for the window system. See Window System Selections.
The variable
file-name-coding-systemspecifies the coding system to use for encoding file names. Emacs encodes file names using that coding system for all file operations. Iffile-name-coding-systemisnil, Emacs uses a default coding system determined by the selected language environment. In the default language environment, any non-ASCII characters in file names are not encoded specially; they appear in the file system using the internal Emacs representation.
Warning: if you change file-name-coding-system (or
the language environment) in the middle of an Emacs session, problems
can result if you have already visited files whose names were encoded
using the earlier coding system and are handled differently under the
new coding system. If you try to save one of these buffers under the
visited file name, saving may use the wrong file name, or it may get
an error. If such a problem happens, use C-x C-w to specify a
new file name for that buffer.
On Windows 2000 and later, Emacs by default uses Unicode APIs to
pass file names to the OS, so the value of
file-name-coding-system is largely ignored. Lisp applications
that need to encode or decode file names on the Lisp level should use
utf-8 coding-system when system-type is
windows-nt; the conversion of UTF-8 encoded file names to the
encoding appropriate for communicating with the OS is performed
internally by Emacs.
Here are the Lisp facilities for working with coding systems:
This function returns a list of all coding system names (symbols). If base-only is non-
nil, the value includes only the base coding systems. Otherwise, it includes alias and variant coding systems as well.
This function returns
tif object is a coding system name ornil.
This function checks the validity of coding-system. If that is valid, it returns coding-system. If coding-system is
nil, the function returnnil. For any other values, it signals an error whoseerror-symboliscoding-system-error(see signal).
This function returns the type of end-of-line (a.k.a. eol) conversion used by coding-system. If coding-system specifies a certain eol conversion, the return value is an integer 0, 1, or 2, standing for
unix,dos, andmac, respectively. If coding-system doesn't specify eol conversion explicitly, the return value is a vector of coding systems, each one with one of the possible eol conversion types, like this:(coding-system-eol-type 'latin-1) => [latin-1-unix latin-1-dos latin-1-mac]If this function returns a vector, Emacs will decide, as part of the text encoding or decoding process, what eol conversion to use. For decoding, the end-of-line format of the text is auto-detected, and the eol conversion is set to match it (e.g., DOS-style CRLF format will imply
doseol conversion). For encoding, the eol conversion is taken from the appropriate default coding system (e.g., default value ofbuffer-file-coding-systemforbuffer-file-coding-system), or from the default eol conversion appropriate for the underlying platform.
This function returns a coding system which is like coding-system except for its eol conversion, which is specified by
eol-type. eol-type should beunix,dos,mac, ornil. If it isnil, the returned coding system determines the end-of-line conversion from the data.eol-type may also be 0, 1 or 2, standing for
unix,dosandmac, respectively.
This function returns a coding system which uses the end-of-line conversion of eol-coding, and the text conversion of text-coding. If text-coding is
nil, it returnsundecided, or one of its variants according to eol-coding.
This function returns a list of coding systems that could be used to encode a text between from and to. All coding systems in the list can safely encode any multibyte characters in that portion of the text.
If the text contains no multibyte characters, the function returns the list
(undecided).
This function returns a list of coding systems that could be used to encode the text of string. All coding systems in the list can safely encode any multibyte characters in string. If the text contains no multibyte characters, this returns the list
(undecided).
This function returns a list of coding systems that could be used to encode all the character sets in the list charsets.
This function checks whether coding systems in the list
coding-system-listcan encode all the characters in the region between start and end. If all of the coding systems in the list can encode the specified text, the function returnsnil. If some coding systems cannot encode some of the characters, the value is an alist, each element of which has the form(coding-system1 pos1 pos2...), meaning that coding-system1 cannot encode characters at buffer positions pos1, pos2, .....start may be a string, in which case end is ignored and the returned value references string indices instead of buffer positions.
This function chooses a plausible coding system for decoding the text from start to end. This text should be a byte sequence, i.e., unibyte text or multibyte text with only ASCII and eight-bit characters (see Explicit Encoding).
Normally this function returns a list of coding systems that could handle decoding the text that was scanned. They are listed in order of decreasing priority. But if highest is non-
nil, then the return value is just one coding system, the one that is highest in priority.If the region contains only ASCII characters except for such ISO-2022 control characters ISO-2022 as
ESC, the value isundecidedor(undecided), or a variant specifying end-of-line conversion, if that can be deduced from the text.If the region contains null bytes, the value is
no-conversion, even if the region contains text encoded in some coding system.
This function is like
detect-coding-regionexcept that it operates on the contents of string instead of bytes in the buffer.
If this variable has a non-
nilvalue, null bytes are ignored when detecting the encoding of a region or a string. This allows the encoding of text that contains null bytes to be correctly detected, such as Info files with Index nodes.
If this variable has a non-
nilvalue, ISO-2022 escape sequences are ignored when detecting the encoding of a region or a string. The result is that no text is ever detected as encoded in some ISO-2022 encoding, and all escape sequences become visible in a buffer. Warning: Use this variable with extreme caution, because many files in the Emacs distribution use ISO-2022 encoding.
This function returns the list of character sets (see Character Sets) supported by coding-system. Some coding systems that support too many character sets to list them all yield special values:
- If coding-system supports all Emacs characters, the value is
(emacs).- If coding-system supports all Unicode characters, the value is
(unicode).- If coding-system supports all ISO-2022 charsets, the value is
iso-2022.- If coding-system supports all the characters in the internal coding system used by Emacs version 21 (prior to the implementation of internal Unicode support), the value is
emacs-mule.
See Process Information, in
particular the description of the functions
process-coding-system and set-process-coding-system, for
how to examine or set the coding systems used for I/O to a subprocess.
This function selects a coding system for encoding specified text, asking the user to choose if necessary. Normally the specified text is the text in the current buffer between from and to. If from is a string, the string specifies the text to encode, and to is ignored.
If the specified text includes raw bytes (see Text Representations),
select-safe-coding-systemsuggestsraw-textfor its encoding.If default-coding-system is non-
nil, that is the first coding system to try; if that can handle the text,select-safe-coding-systemreturns that coding system. It can also be a list of coding systems; then the function tries each of them one by one. After trying all of them, it next tries the current buffer's value ofbuffer-file-coding-system(if it is notundecided), then the default value ofbuffer-file-coding-systemand finally the user's most preferred coding system, which the user can set using the commandprefer-coding-system(see Recognizing Coding Systems).If one of those coding systems can safely encode all the specified text,
select-safe-coding-systemchooses it and returns it. Otherwise, it asks the user to choose from a list of coding systems which can encode all the text, and returns the user's choice.default-coding-system can also be a list whose first element is t and whose other elements are coding systems. Then, if no coding system in the list can handle the text,
select-safe-coding-systemqueries the user immediately, without trying any of the three alternatives described above.The optional argument accept-default-p, if non-
nil, should be a function to determine whether a coding system selected without user interaction is acceptable.select-safe-coding-systemcalls this function with one argument, the base coding system of the selected coding system. If accept-default-p returnsnil,select-safe-coding-systemrejects the silently selected coding system, and asks the user to select a coding system from a list of possible candidates.If the variable
select-safe-coding-system-accept-default-pis non-nil, it should be a function taking a single argument. It is used in place of accept-default-p, overriding any value supplied for this argument.As a final step, before returning the chosen coding system,
select-safe-coding-systemchecks whether that coding system is consistent with what would be selected if the contents of the region were read from a file. (If not, this could lead to data corruption in a file subsequently re-visited and edited.) Normally,select-safe-coding-systemusesbuffer-file-nameas the file for this purpose, but if file is non-nil, it uses that file instead (this can be relevant forwrite-regionand similar functions). If it detects an apparent inconsistency,select-safe-coding-systemqueries the user before selecting the coding system.
Here are two functions you can use to let the user specify a coding system, with completion. See Completion.
This function reads a coding system using the minibuffer, prompting with string prompt, and returns the coding system name as a symbol. If the user enters null input, default specifies which coding system to return. It should be a symbol or a string.
This function reads a coding system using the minibuffer, prompting with string prompt, and returns the coding system name as a symbol. If the user tries to enter null input, it asks the user to try again. See Coding Systems.
This section describes variables that specify the default coding system for certain files or when running certain subprograms, and the function that I/O operations use to access them.
The idea of these variables is that you set them once and for all to the
defaults you want, and then do not change them again. To specify a
particular coding system for a particular operation in a Lisp program,
don't change these variables; instead, override them using
coding-system-for-read and coding-system-for-write
(see Specifying Coding Systems).
This variable is an alist of text patterns and corresponding coding systems. Each element has the form
(regexp.coding-system); a file whose first few kilobytes match regexp is decoded with coding-system when its contents are read into a buffer. The settings in this alist take priority overcoding:tags in the files and the contents offile-coding-system-alist(see below). The default value is set so that Emacs automatically recognizes mail files in Babyl format and reads them with no code conversions.
This variable is an alist that specifies the coding systems to use for reading and writing particular files. Each element has the form
(pattern.coding), where pattern is a regular expression that matches certain file names. The element applies to file names that match pattern.The cdr of the element, coding, should be either a coding system, a cons cell containing two coding systems, or a function name (a symbol with a function definition). If coding is a coding system, that coding system is used for both reading the file and writing it. If coding is a cons cell containing two coding systems, its car specifies the coding system for decoding, and its cdr specifies the coding system for encoding.
If coding is a function name, the function should take one argument, a list of all arguments passed to
find-operation-coding-system. It must return a coding system or a cons cell containing two coding systems. This value has the same meaning as described above.If coding (or what returned by the above function) is
undecided, the normal code-detection is performed.
This variable is an alist that specifies the coding systems to use for reading and writing particular files. Its form is like that of
file-coding-system-alist, but, unlike the latter, this variable takes priority over anycoding:tags in the file.
This variable is an alist specifying which coding systems to use for a subprocess, depending on which program is running in the subprocess. It works like
file-coding-system-alist, except that pattern is matched against the program name used to start the subprocess. The coding system or systems specified in this alist are used to initialize the coding systems used for I/O to the subprocess, but you can specify other coding systems later usingset-process-coding-system.
Warning: Coding systems such as undecided, which
determine the coding system from the data, do not work entirely reliably
with asynchronous subprocess output. This is because Emacs handles
asynchronous subprocess output in batches, as it arrives. If the coding
system leaves the character code conversion unspecified, or leaves the
end-of-line conversion unspecified, Emacs must try to detect the proper
conversion from one batch at a time, and this does not always work.
Therefore, with an asynchronous subprocess, if at all possible, use a
coding system which determines both the character code conversion and
the end of line conversion—that is, one like latin-1-unix,
rather than undecided or latin-1.
This variable is an alist that specifies the coding system to use for network streams. It works much like
file-coding-system-alist, with the difference that the pattern in an element may be either a port number or a regular expression. If it is a regular expression, it is matched against the network service name used to open the network stream.
This variable specifies the coding systems to use for subprocess (and network stream) input and output, when nothing else specifies what to do.
The value should be a cons cell of the form
(input-coding.output-coding). Here input-coding applies to input from the subprocess, and output-coding applies to output to it.
This variable holds a list of functions that try to determine a coding system for a file based on its undecoded contents.
Each function in this list should be written to look at text in the current buffer, but should not modify it in any way. The buffer will contain undecoded text of parts of the file. Each function should take one argument, size, which tells it how many characters to look at, starting from point. If the function succeeds in determining a coding system for the file, it should return that coding system. Otherwise, it should return
nil.If a file has a `coding:' tag, that takes precedence, so these functions won't be called.
This function tries to determine a suitable coding system for filename. It examines the buffer visiting the named file, using the variables documented above in sequence, until it finds a match for one of the rules specified by these variables. It then returns a cons cell of the form
(coding.source), where coding is the coding system to use and source is a symbol, one ofauto-coding-alist,auto-coding-regexp-alist,:coding, orauto-coding-functions, indicating which one supplied the matching rule. The value:codingmeans the coding system was specified by thecoding:tag in the file (see coding tag). The order of looking for a matching rule isauto-coding-alistfirst, thenauto-coding-regexp-alist, then thecoding:tag, and lastlyauto-coding-functions. If no matching rule was found, the function returnsnil.The second argument size is the size of text, in characters, following point. The function examines text only within size characters after point. Normally, the buffer should be positioned at the beginning when this function is called, because one of the places for the
coding:tag is the first one or two lines of the file; in that case, size should be the size of the buffer.
This function returns a suitable coding system for file filename. It uses
find-auto-codingto find the coding system. If no coding system could be determined, the function returnsnil. The meaning of the argument size is like infind-auto-coding.
This function returns the coding system to use (by default) for performing operation with arguments. The value has this form:
(decoding-system . encoding-system)The first element, decoding-system, is the coding system to use for decoding (in case operation does decoding), and encoding-system is the coding system for encoding (in case operation does encoding).
The argument operation is a symbol; it should be one of
write-region,start-process,call-process,call-process-region,insert-file-contents, oropen-network-stream. These are the names of the Emacs I/O primitives that can do character code and eol conversion.The remaining arguments should be the same arguments that might be given to the corresponding I/O primitive. Depending on the primitive, one of those arguments is selected as the target. For example, if operation does file I/O, whichever argument specifies the file name is the target. For subprocess primitives, the process name is the target. For
open-network-stream, the target is the service name or port number.Depending on operation, this function looks up the target in
file-coding-system-alist,process-coding-system-alist, ornetwork-coding-system-alist. If the target is found in the alist,find-operation-coding-systemreturns its association in the alist; otherwise it returnsnil.If operation is
insert-file-contents, the argument corresponding to the target may be a cons cell of the form(filename.buffer). In that case, filename is a file name to look up infile-coding-system-alist, and buffer is a buffer that contains the file's contents (not yet decoded). Iffile-coding-system-alistspecifies a function to call for this file, and that function needs to examine the file's contents (as it usually does), it should examine the contents of buffer instead of reading the file.
You can specify the coding system for a specific operation by binding
the variables coding-system-for-read and/or
coding-system-for-write.
If this variable is non-
nil, it specifies the coding system to use for reading a file, or for input from a synchronous subprocess.It also applies to any asynchronous subprocess or network stream, but in a different way: the value of
coding-system-for-readwhen you start the subprocess or open the network stream specifies the input decoding method for that subprocess or network stream. It remains in use for that subprocess or network stream unless and until overridden.The right way to use this variable is to bind it with
letfor a specific I/O operation. Its global value is normallynil, and you should not globally set it to any other value. Here is an example of the right way to use the variable:;; Read the file with no character code conversion. (let ((coding-system-for-read 'no-conversion)) (insert-file-contents filename))When its value is non-
nil, this variable takes precedence over all other methods of specifying a coding system to use for input, includingfile-coding-system-alist,process-coding-system-alistandnetwork-coding-system-alist.
This works much like
coding-system-for-read, except that it applies to output rather than input. It affects writing to files, as well as sending output to subprocesses and net connections.When a single operation does both input and output, as do
call-process-regionandstart-process, bothcoding-system-for-readandcoding-system-for-writeaffect it.
When this variable is non-
nil, no end-of-line conversion is done, no matter which coding system is specified. This applies to all the Emacs I/O and subprocess primitives, and to the explicit encoding and decoding functions (see Explicit Encoding).
Sometimes, you need to prefer several coding systems for some
operation, rather than fix a single one. Emacs lets you specify a
priority order for using coding systems. This ordering affects the
sorting of lists of coding systems returned by functions such as
find-coding-systems-region (see Lisp and Coding Systems).
This function returns the list of coding systems in the order of their current priorities. Optional argument highestp, if non-
nil, means return only the highest priority coding system.
This function puts coding-systems at the beginning of the priority list for coding systems, thus making their priority higher than all the rest.
This macro execute body, like
progndoes (see progn), with coding-systems at the front of the priority list for coding systems. coding-systems should be a list of coding systems to prefer during execution of body.
All the operations that transfer text in and out of Emacs have the ability to use a coding system to encode or decode the text. You can also explicitly encode and decode text using the functions in this section.
The result of encoding, and the input to decoding, are not ordinary text. They logically consist of a series of byte values; that is, a series of ASCII and eight-bit characters. In unibyte buffers and strings, these characters have codes in the range 0 through #xFF (255). In a multibyte buffer or string, eight-bit characters have character codes higher than #xFF (see Text Representations), but Emacs transparently converts them to their single-byte values when you encode or decode such text.
The usual way to read a file into a buffer as a sequence of bytes, so
you can decode the contents explicitly, is with
insert-file-contents-literally (see Reading from Files);
alternatively, specify a non-nil rawfile argument when
visiting a file with find-file-noselect. These methods result in
a unibyte buffer.
The usual way to use the byte sequence that results from explicitly
encoding text is to copy it to a file or process—for example, to write
it with write-region (see Writing to Files), and suppress
encoding by binding coding-system-for-write to
no-conversion.
Here are the functions to perform explicit encoding or decoding. The
encoding functions produce sequences of bytes; the decoding functions
are meant to operate on sequences of bytes. All of these functions
discard text properties. They also set last-coding-system-used
to the precise coding system they used.
This command encodes the text from start to end according to coding system coding-system. Normally, the encoded text replaces the original text in the buffer, but the optional argument destination can change that. If destination is a buffer, the encoded text is inserted in that buffer after point (point does not move); if it is
t, the command returns the encoded text as a unibyte string without inserting it.If encoded text is inserted in some buffer, this command returns the length of the encoded text.
The result of encoding is logically a sequence of bytes, but the buffer remains multibyte if it was multibyte before, and any 8-bit bytes are converted to their multibyte representation (see Text Representations).
Do not use
undecidedfor coding-system when encoding text, since that may lead to unexpected results. Instead, useselect-safe-coding-system(see select-safe-coding-system) to suggest a suitable encoding, if there's no obvious pertinent value for coding-system.
This function encodes the text in string according to coding system coding-system. It returns a new string containing the encoded text, except when nocopy is non-
nil, in which case the function may return string itself if the encoding operation is trivial. The result of encoding is a unibyte string.
This command decodes the text from start to end according to coding system coding-system. To make explicit decoding useful, the text before decoding ought to be a sequence of byte values, but both multibyte and unibyte buffers are acceptable (in the multibyte case, the raw byte values should be represented as eight-bit characters). Normally, the decoded text replaces the original text in the buffer, but the optional argument destination can change that. If destination is a buffer, the decoded text is inserted in that buffer after point (point does not move); if it is
t, the command returns the decoded text as a multibyte string without inserting it.If decoded text is inserted in some buffer, this command returns the length of the decoded text.
This command puts a
charsettext property on the decoded text. The value of the property states the character set used to decode the original text.
This function decodes the text in string according to coding-system. It returns a new string containing the decoded text, except when nocopy is non-
nil, in which case the function may return string itself if the decoding operation is trivial. To make explicit decoding useful, the contents of string ought to be a unibyte string with a sequence of byte values, but a multibyte string is also acceptable (assuming it contains 8-bit bytes in their multibyte form).If optional argument buffer specifies a buffer, the decoded text is inserted in that buffer after point (point does not move). In this case, the return value is the length of the decoded text.
This function puts a
charsettext property on the decoded text. The value of the property states the character set used to decode the original text:(decode-coding-string "Gr\374ss Gott" 'latin-1) => #("Grüss Gott" 0 9 (charset iso-8859-1))
This function decodes the text from from to to as if it were being read from file filename using
insert-file-contentsusing the rest of the arguments provided.The normal way to use this function is after reading text from a file without decoding, if you decide you would rather have decoded it. Instead of deleting the text and reading it again, this time with decoding, you can call this function.
Emacs can use coding systems to decode keyboard input and encode
terminal output. This is useful for terminals that transmit or
display text using a particular encoding, such as Latin-1. Emacs does
not set last-coding-system-used when encoding or decoding
terminal I/O.
This function returns the coding system used for decoding keyboard input from terminal. A value of
no-conversionmeans no decoding is done. If terminal is omitted ornil, it means the selected frame's terminal. See Multiple Terminals.
This command specifies coding-system as the coding system to use for decoding keyboard input from terminal. If coding-system is
nil, that means not to decode keyboard input. If terminal is a frame, it means that frame's terminal; if it isnil, that means the currently selected frame's terminal. See Multiple Terminals.
This function returns the coding system that is in use for encoding terminal output from terminal. A value of
no-conversionmeans no encoding is done. If terminal is a frame, it means that frame's terminal; if it isnil, that means the currently selected frame's terminal.
This command specifies coding-system as the coding system to use for encoding terminal output from terminal. If coding-system is
nil, that means not to encode terminal output. If terminal is a frame, it means that frame's terminal; if it isnil, that means the currently selected frame's terminal.
Input methods provide convenient ways of entering non-ASCII characters from the keyboard. Unlike coding systems, which translate non-ASCII characters to and from encodings meant to be read by programs, input methods provide human-friendly commands. (See Input Methods, for information on how users use input methods to enter text.) How to define input methods is not yet documented in this manual, but here we describe how to use them.
Each input method has a name, which is currently a string; in the future, symbols may also be usable as input method names.
This variable holds the name of the input method now active in the current buffer. (It automatically becomes local in each buffer when set in any fashion.) It is
nilif no input method is active in the buffer now.
This variable holds the default input method for commands that choose an input method. Unlike
current-input-method, this variable is normally global.
This command activates input method input-method for the current buffer. It also sets
default-input-methodto input-method. If input-method isnil, this command deactivates any input method for the current buffer.
This function reads an input method name with the minibuffer, prompting with prompt. If default is non-
nil, that is returned by default, if the user enters empty input. However, if inhibit-null is non-nil, empty input signals an error.The returned value is a string.
This variable defines all the supported input methods. Each element defines one input method, and should have the form:
(input-method language-env activate-func title description args...)Here input-method is the input method name, a string; language-env is another string, the name of the language environment this input method is recommended for. (That serves only for documentation purposes.)
activate-func is a function to call to activate this method. The args, if any, are passed as arguments to activate-func. All told, the arguments to activate-func are input-method and the args.
title is a string to display in the mode line while this method is active. description is a string describing this method and what it is good for.
The fundamental interface to input methods is through the
variable input-method-function. See Reading One Event,
and Invoking the Input Method.
In POSIX, locales control which language to use in language-related features. These Emacs variables control how Emacs interacts with these features.
This variable specifies the coding system to use for decoding system error messages and—on X Window system only—keyboard input, for sending batch output to the standard output and error streams, for encoding the format argument to
format-time-string, and for decoding the return value offormat-time-string.
This variable specifies the locale to use for generating system error messages. Changing the locale can cause messages to come out in a different language or in a different orthography. If the variable is
nil, the locale is specified by environment variables in the usual POSIX fashion.
This variable specifies the locale to use for formatting time values. Changing the locale can cause messages to appear according to the conventions of a different language. If the variable is
nil, the locale is specified by environment variables in the usual POSIX fashion.
This function returns locale data item for the current POSIX locale, if available. item should be one of these symbols:
codeset- Return the character set as a string (locale item
CODESET).
days- Return a 7-element vector of day names (locale items
DAY_1throughDAY_7);
months- Return a 12-element vector of month names (locale items
MON_1throughMON_12).
paper- Return a list
(width height)for the default paper size measured in millimeters (locale itemsPAPER_WIDTHandPAPER_HEIGHT).If the system can't provide the requested information, or if item is not one of those symbols, the value is
nil. All strings in the return value are decoded usinglocale-coding-system. See Locales, for more information about locales and locale items.
GNU Emacs provides two ways to search through a buffer for specified text: exact string searches and regular expression searches. After a regular expression search, you can examine the match data to determine which text matched the whole regular expression or various portions of it.
The `skip-chars...' functions also perform a kind of searching. See Skipping Characters. To search for changes in character properties, see Property Search.
These are the primitive functions for searching through the text in a
buffer. They are meant for use in programs, but you may call them
interactively. If you do so, they prompt for the search string; the
arguments limit and noerror are nil, and repeat
is 1. For more details on interactive searching, see Searching and Replacement.
These search functions convert the search string to multibyte if the buffer is multibyte; they convert the search string to unibyte if the buffer is unibyte. See Text Representations.
This function searches forward from point for an exact match for string. If successful, it sets point to the end of the occurrence found, and returns the new value of point. If no match is found, the value and side effects depend on noerror (see below).
In the following example, point is initially at the beginning of the line. Then
(search-forward "fox")moves point after the last letter of `fox':---------- Buffer: foo ---------- -!-The quick brown fox jumped over the lazy dog. ---------- Buffer: foo ---------- (search-forward "fox") => 20 ---------- Buffer: foo ---------- The quick brown fox-!- jumped over the lazy dog. ---------- Buffer: foo ----------The argument limit specifies the bound to the search, and should be a position in the current buffer. No match extending after that position is accepted. If limit is omitted or
nil, it defaults to the end of the accessible portion of the buffer.What happens when the search fails depends on the value of noerror. If noerror is
nil, asearch-failederror is signaled. If noerror ist,search-forwardreturnsniland does nothing. If noerror is neithernilnort, thensearch-forwardmoves point to the upper bound and returnsnil.The argument noerror only affects valid searches which fail to find a match. Invalid arguments cause errors regardless of noerror.
If repeat is a positive number n, it serves as a repeat count: the search is repeated n times, each time starting at the end of the previous time's match. If these successive searches succeed, the function succeeds, moving point and returning its new value. Otherwise the search fails, with results depending on the value of noerror, as described above. If repeat is a negative number -n, it serves as a repeat count of n for a search in the opposite (backward) direction.
This function searches backward from point for string. It is like
search-forward, except that it searches backwards rather than forwards. Backward searches leave point at the beginning of the match.
This function searches forward from point for a word match for string. If it finds a match, it sets point to the end of the match found, and returns the new value of point.
Word matching regards string as a sequence of words, disregarding punctuation that separates them. It searches the buffer for the same sequence of words. Each word must be distinct in the buffer (searching for the word `ball' does not match the word `balls'), but the details of punctuation and spacing are ignored (searching for `ball boy' does match `ball. Boy!').
In this example, point is initially at the beginning of the buffer; the search leaves it between the `y' and the `!'.
---------- Buffer: foo ---------- -!-He said "Please! Find the ball boy!" ---------- Buffer: foo ---------- (word-search-forward "Please find the ball, boy.") => 39 ---------- Buffer: foo ---------- He said "Please! Find the ball boy-!-!" ---------- Buffer: foo ----------If limit is non-
nil, it must be a position in the current buffer; it specifies the upper bound to the search. The match found must not extend after that position.If noerror is
nil, thenword-search-forwardsignals an error if the search fails. If noerror ist, then it returnsnilinstead of signaling an error. If noerror is neithernilnort, it moves point to limit (or the end of the accessible portion of the buffer) and returnsnil.If repeat is non-
nil, then the search is repeated that many times. Point is positioned at the end of the last match.Internally,
word-search-forwardand related functions use the functionword-search-regexpto convert string to a regular expression that ignores punctuation.
This command is identical to
word-search-forward, except that the beginning or the end of string need not match a word boundary, unless string begins or ends in whitespace. For instance, searching for `ball boy' matches `ball boyee', but does not match `balls boy'.
This function searches backward from point for a word match to string. This function is just like
word-search-forwardexcept that it searches backward and normally leaves point at the beginning of the match.
This command is identical to
word-search-backward, except that the beginning or the end of string need not match a word boundary, unless string begins or ends in whitespace.
By default, searches in Emacs ignore the case of the text they are searching through; if you specify searching for `FOO', then `Foo' or `foo' is also considered a match. This applies to regular expressions, too; thus, `[aB]' would match `a' or `A' or `b' or `B'.
If you do not want this feature, set the variable
case-fold-search to nil. Then all letters must match
exactly, including case. This is a buffer-local variable; altering the
variable affects only the current buffer. (See Intro to Buffer-Local.) Alternatively, you may change the default value.
In Lisp code, you will more typically use let to bind
case-fold-search to the desired value.
Note that the user-level incremental search feature handles case distinctions differently. When the search string contains only lower case letters, the search ignores case, but when the search string contains one or more upper case letters, the search becomes case-sensitive. But this has nothing to do with the searching functions used in Lisp code. See Incremental Search.
This buffer-local variable determines whether searches should ignore case. If the variable is
nilthey do not ignore case; otherwise (and by default) they do ignore case.
This variable determines whether the higher-level replacement functions should preserve case. If the variable is
nil, that means to use the replacement text verbatim. A non-nilvalue means to convert the case of the replacement text according to the text being replaced.This variable is used by passing it as an argument to the function
replace-match. See Replacing Match.
A regular expression, or regexp for short, is a pattern that denotes a (possibly infinite) set of strings. Searching for matches for a regexp is a very powerful operation. This section explains how to write regexps; the following section says how to search for them.
For interactive development of regular expressions, you can use the M-x re-builder command. It provides a convenient interface for creating regular expressions, by giving immediate visual feedback in a separate buffer. As you edit the regexp, all its matches in the target buffer are highlighted. Each parenthesized sub-expression of the regexp is shown in a distinct face, which makes it easier to verify even very complex regexps.
Regular expressions have a syntax in which a few characters are special constructs and the rest are ordinary. An ordinary character is a simple regular expression that matches that character and nothing else. The special characters are `.', `*', `+', `?', `[', `^', `$', and `\'; no new special characters will be defined in the future. The character `]' is special if it ends a character alternative (see later). The character `-' is special inside a character alternative. A `[:' and balancing `:]' enclose a character class inside a character alternative. Any other character appearing in a regular expression is ordinary, unless a `\' precedes it.
For example, `f' is not a special character, so it is ordinary, and therefore `f' is a regular expression that matches the string `f' and no other string. (It does not match the string `fg', but it does match a part of that string.) Likewise, `o' is a regular expression that matches only `o'.
Any two regular expressions a and b can be concatenated. The result is a regular expression that matches a string if a matches some amount of the beginning of that string and b matches the rest of the string.
As a simple example, we can concatenate the regular expressions `f' and `o' to get the regular expression `fo', which matches only the string `fo'. Still trivial. To do something more powerful, you need to use one of the special regular expression constructs.
Here is a list of the characters that are special in a regular expression.
`*' always applies to the smallest possible preceding expression. Thus, `fo*' has a repeating `o', not a repeating `fo'. It matches `f', `fo', `foo', and so on.
The matcher processes a `*' construct by matching, immediately, as many repetitions as can be found. Then it continues with the rest of the pattern. If that fails, backtracking occurs, discarding some of the matches of the `*'-modified construct in the hope that that will make it possible to match the rest of the pattern. For example, in matching `ca*ar' against the string `caaar', the `a*' first tries to match all three `a's; but the rest of the pattern is `ar' and there is only `r' left to match, so this try fails. The next alternative is for `a*' to match only two `a's. With this choice, the rest of the regexp matches successfully.
Warning: Nested repetition operators can run for an
indefinitely long time, if they lead to ambiguous matching. For
example, trying to match the regular expression `\(x+y*\)*a'
against the string `xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxz' could
take hours before it ultimately fails. Emacs must try each way of
grouping the `x's before concluding that none of them can work.
Even worse, `\(x*\)*' can match the null string in infinitely
many ways, so it causes an infinite loop. To avoid these problems,
check nested repetitions carefully, to make sure that they do not
cause combinatorial explosions in backtracking.
For example, the regular expression `c[ad]*a' when applied to the
string `cdaaada' matches the whole string; but the regular
expression `c[ad]*?a', applied to that same string, matches just
`cda'. (The smallest possible match here for `[ad]*?' that
permits the whole expression to match is `d'.)
Thus, `[ad]' matches either one `a' or one `d', and `[ad]*' matches any string composed of just `a's and `d's (including the empty string). It follows that `c[ad]*r' matches `cr', `car', `cdr', `caddaar', etc.
You can also include character ranges in a character alternative, by writing the starting and ending characters with a `-' between them. Thus, `[a-z]' matches any lower-case ASCII letter. Ranges may be intermixed freely with individual characters, as in `[a-z$%.]', which matches any lower case ASCII letter or `$', `%' or period.
If case-fold-search is non-nil, `[a-z]' also
matches upper-case letters. Note that a range like `[a-z]' is
not affected by the locale's collation sequence, it always represents
a sequence in ASCII order.
Note also that the usual regexp special characters are not special inside a character alternative. A completely different set of characters is special inside character alternatives: `]', `-' and `^'.
To include a `]' in a character alternative, you must make it the first character. For example, `[]a]' matches `]' or `a'. To include a `-', write `-' as the first or last character of the character alternative, or put it after a range. Thus, `[]-]' matches both `]' and `-'. (As explained below, you cannot use `\]' to include a `]' inside a character alternative, since `\' is not special there.)
To include `^' in a character alternative, put it anywhere but at the beginning.
If a range starts with a unibyte character c and ends with a multibyte character c2, the range is divided into two parts: one spans the unibyte characters `c..?\377', the other the multibyte characters `c1..c2', where c1 is the first character of the charset to which c2 belongs.
A character alternative can also specify named character classes
(see Char Classes). This is a POSIX feature. For example,
`[[:ascii:]]' matches any ASCII character.
Using a character class is equivalent to mentioning each of the
characters in that class; but the latter is not feasible in practice,
since some classes include thousands of different characters.
`^' is not special in a character alternative unless it is the first character. The character following the `^' is treated as if it were first (in other words, `-' and `]' are not special there).
A complemented character alternative can match a newline, unless newline is
mentioned as one of the characters not to match. This is in contrast to
the handling of regexps in programs such as grep.
You can specify named character classes, just like in character
alternatives. For instance, `[^[:ascii:]]' matches any
non-ASCII character. See Char Classes.
When matching a string instead of a buffer, `^' matches at the beginning of the string or after a newline character.
For historical compatibility reasons, `^' can be used only at the
beginning of the regular expression, or after `\(', `\(?:'
or `\|'.
When matching a string instead of a buffer, `$' matches at the end of the string or before a newline character.
For historical compatibility reasons, `$' can be used only at the
end of the regular expression, or before `\)' or `\|'.
Because `\' quotes special characters, `\$' is a regular expression that matches only `$', and `\[' is a regular expression that matches only `[', and so on.
Note that `\' also has special meaning in the read syntax of Lisp
strings (see String Type), and must be quoted with `\'. For
example, the regular expression that matches the `\' character is
`\\'. To write a Lisp string that contains the characters
`\\', Lisp syntax requires you to quote each `\' with another
`\'. Therefore, the read syntax for a regular expression matching
`\' is "\\\\".
Please note: For historical compatibility, special characters are treated as ordinary ones if they are in contexts where their special meanings make no sense. For example, `*foo' treats `*' as ordinary since there is no preceding expression on which the `*' can act. It is poor practice to depend on this behavior; quote the special character anyway, regardless of where it appears.
As a `\' is not special inside a character alternative, it can
never remove the special meaning of `-' or `]'. So you
should not quote these characters when they have no special meaning
either. This would not clarify anything, since backslashes can
legitimately precede these characters where they have special
meaning, as in `[^\]' ("[^\\]" for Lisp string syntax),
which matches any single character except a backslash.
In practice, most `]' that occur in regular expressions close a character alternative and hence are special. However, occasionally a regular expression may try to match a complex pattern of literal `[' and `]'. In such situations, it sometimes may be necessary to carefully parse the regexp from the start to determine which square brackets enclose a character alternative. For example, `[^][]]' consists of the complemented character alternative `[^][]' (which matches any single character that is not a square bracket), followed by a literal `]'.
The exact rules are that at the beginning of a regexp, `[' is special and `]' not. This lasts until the first unquoted `[', after which we are in a character alternative; `[' is no longer special (except when it starts a character class) but `]' is special, unless it immediately follows the special `[' or that `[' followed by a `^'. This lasts until the next special `]' that does not end a character class. This ends the character alternative and restores the ordinary syntax of regular expressions; an unquoted `[' is special again and a `]' not.
Here is a table of the classes you can use in a character alternative, and what they mean:
case-fold-search is
non-nil, this also matches any upper-case letter.
case-fold-search is
non-nil, this also matches any lower-case letter.
For the most part, `\' followed by any character matches only that character. However, there are several exceptions: certain sequences starting with `\' that have special meanings. Here is a table of the special `\' constructs.
Thus, `foo\|bar' matches either `foo' or `bar' but no other string.
`\|' applies to the largest possible surrounding expressions. Only a surrounding `\( ... \)' grouping can limit the grouping power of `\|'.
If you need full backtracking capability to handle multiple uses of
`\|', use the POSIX regular expression functions (see POSIX Regexps).
For example, `c[ad]\{1,2\}r' matches the strings `car',
`cdr', `caar', `cadr', `cdar', and `cddr', and
nothing else.
`\{0,1\}' or `\{,1\}' is equivalent to `?'.
`\{0,\}' or `\{,\}' is equivalent to `*'.
`\{1,\}' is equivalent to `+'.
This last application is not a consequence of the idea of a
parenthetical grouping; it is a separate feature that was assigned as a
second meaning to the same `\( ... \)' construct because, in
practice, there was usually no conflict between the two meanings. But
occasionally there is a conflict, and that led to the introduction of
shy groups.
Shy groups are also called non-capturing or unnumbered
groups.
In other words, after the end of a group, the matcher remembers the beginning and end of the text matched by that group. Later on in the regular expression you can use `\' followed by digit to match that same text, whatever it may have been.
The strings matching the first nine grouping constructs appearing in the entire regular expression passed to a search or matching function are assigned numbers 1 through 9 in the order that the open parentheses appear in the regular expression. So you can use `\1' through `\9' to refer to the text matched by the corresponding grouping constructs.
For example, `\(.*\)\1' matches any newline-free string that is composed of two identical halves. The `\(.*\)' matches the first half, which may be anything, but the `\1' that follows must match the same exact text.
If a `\( ... \)' construct matches more than once (which can happen, for instance, if it is followed by `*'), only the last match is recorded.
If a particular grouping construct in the regular expression was never
matched—for instance, if it appears inside of an alternative that
wasn't used, or inside of a repetition that repeated zero times—then
the corresponding `\digit' construct never matches
anything. To use an artificial example, `\(foo\(b*\)\|lose\)\2'
cannot match `lose': the second alternative inside the larger
group matches it, but then `\2' is undefined and can't match
anything. But it can match `foobb', because the first
alternative matches `foob' and `\2' matches `b'.
define-category function (see Categories).
The following regular expression constructs match the empty string—that is, they don't use up any characters—but whether they match depends on the context. For all, the beginning and end of the accessible portion of the buffer are treated as if they were the actual beginning and end of the buffer.
`\b' matches at the beginning or end of the buffer (or string)
regardless of what text appears next to it.
Not every string is a valid regular expression. For example, a string
that ends inside a character alternative without a terminating `]'
is invalid, and so is a string that ends with a single `\'. If
an invalid regular expression is passed to any of the search functions,
an invalid-regexp error is signaled.
Here is a complicated regexp which was formerly used by Emacs to
recognize the end of a sentence together with any whitespace that
follows. (Nowadays Emacs uses a similar but more complex default
regexp constructed by the function sentence-end.
See Standard Regexps.)
Below, we show first the regexp as a string in Lisp syntax (to distinguish spaces from tab characters), and then the result of evaluating it. The string constant begins and ends with a double-quote. `\"' stands for a double-quote as part of the string, `\\' for a backslash as part of the string, `\t' for a tab and `\n' for a newline.
"[.?!][]\"')}]*\\($\\| $\\|\t\\| \\)[ \t\n]*"
=> "[.?!][]\"')}]*\\($\\| $\\| \\| \\)[
]*"
In the output, tab and newline appear as themselves.
This regular expression contains four parts in succession and can be deciphered as follows:
[.?!][]\"')}]*\" is Lisp syntax for a double-quote in
a string. The `*' at the end indicates that the immediately
preceding regular expression (a character alternative, in this case) may be
repeated zero or more times.
\\($\\| $\\|\t\\| \\)[ \t\n]*These functions operate on regular expressions.
This function returns a regular expression whose only exact match is string. Using this regular expression in
looking-atwill succeed only if the next characters in the buffer are string; using it in a search function will succeed if the text being searched contains string. See Regexp Search.This allows you to request an exact string match or search when calling a function that wants a regular expression.
(regexp-quote "^The cat$") => "\\^The cat\\$"One use of
regexp-quoteis to combine an exact string match with context described as a regular expression. For example, this searches for the string that is the value of string, surrounded by whitespace:(re-search-forward (concat "\\s-" (regexp-quote string) "\\s-"))
This function returns an efficient regular expression that will match any of the strings in the list strings. This is useful when you need to make matching or searching as fast as possible—for example, for Font Lock mode17.
If the optional argument paren is non-
nil, then the returned regular expression is always enclosed by at least one parentheses-grouping construct. If paren iswords, then that construct is additionally surrounded by `\<' and `\>'; alternatively, if paren issymbols, then that construct is additionally surrounded by `\_<' and `\_>' (symbolsis often appropriate when matching programming-language keywords and the like).This simplified definition of
regexp-optproduces a regular expression which is equivalent to the actual value (but not as efficient):(defun regexp-opt (strings &optional paren) (let ((open-paren (if paren "\\(" "")) (close-paren (if paren "\\)" ""))) (concat open-paren (mapconcat 'regexp-quote strings "\\|") close-paren)))
This function returns the total number of grouping constructs (parenthesized expressions) in regexp. This does not include shy groups (see Regexp Backslash).
This function returns a regular expression matching a character in the list of characters chars.
(regexp-opt-charset '(?a ?b ?c ?d ?e)) => "[a-e]"
In GNU Emacs, you can search for the next match for a regular
expression (see Syntax of Regexps) either incrementally or not.
For incremental search commands, see Regular Expression Search. Here we describe
only the search functions useful in programs. The principal one is
re-search-forward.
These search functions convert the regular expression to multibyte if the buffer is multibyte; they convert the regular expression to unibyte if the buffer is unibyte. See Text Representations.
This function searches forward in the current buffer for a string of text that is matched by the regular expression regexp. The function skips over any amount of text that is not matched by regexp, and leaves point at the end of the first match found. It returns the new value of point.
If limit is non-
nil, it must be a position in the current buffer. It specifies the upper bound to the search. No match extending after that position is accepted.If repeat is supplied, it must be a positive number; the search is repeated that many times; each repetition starts at the end of the previous match. If all these successive searches succeed, the search succeeds, moving point and returning its new value. Otherwise the search fails. What
re-search-forwarddoes when the search fails depends on the value of noerror:
nil- Signal a
search-failederror.
t- Do nothing and return
nil.
- anything else
- Move point to limit (or the end of the accessible portion of the buffer) and return
nil.In the following example, point is initially before the `T'. Evaluating the search call moves point to the end of that line (between the `t' of `hat' and the newline).
---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (re-search-forward "[a-z]+" nil t 5) => 27 ---------- Buffer: foo ---------- I read "The cat in the hat-!- comes back" twice. ---------- Buffer: foo ----------
This function searches backward in the current buffer for a string of text that is matched by the regular expression regexp, leaving point at the beginning of the first text found.
This function is analogous to
re-search-forward, but they are not simple mirror images.re-search-forwardfinds the match whose beginning is as close as possible to the starting point. Ifre-search-backwardwere a perfect mirror image, it would find the match whose end is as close as possible. However, in fact it finds the match whose beginning is as close as possible (and yet ends before the starting point). The reason for this is that matching a regular expression at a given spot always works from beginning to end, and starts at a specified beginning position.A true mirror-image of
re-search-forwardwould require a special feature for matching regular expressions from end to beginning. It's not worth the trouble of implementing that.
This function returns the index of the start of the first match for the regular expression regexp in string, or
nilif there is no match. If start is non-nil, the search starts at that index in string.For example,
(string-match "quick" "The quick brown fox jumped quickly.") => 4 (string-match "quick" "The quick brown fox jumped quickly." 8) => 27The index of the first character of the string is 0, the index of the second character is 1, and so on.
If this function finds a match, the index of the first character beyond the match is available as
(match-end 0). See Match Data.(string-match "quick" "The quick brown fox jumped quickly." 8) => 27 (match-end 0) => 32
This predicate function does what
string-matchdoes, but it avoids modifying the match data.
This function determines whether the text in the current buffer directly following point matches the regular expression regexp. “Directly following” means precisely that: the search is “anchored” and it can succeed only starting with the first character following point. The result is
tif so,nilotherwise.This function does not move point, but it does update the match data. See Match Data. If you need to test for a match without modifying the match data, use
looking-at-p, described below.In this example, point is located directly before the `T'. If it were anywhere else, the result would be
nil.---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-at "The cat in the hat$") => t
This function returns
tif regexp matches the text immediately before point (i.e., ending at point), andnilotherwise.Because regular expression matching works only going forward, this is implemented by searching backwards from point for a match that ends at point. That can be quite slow if it has to search a long distance. You can bound the time required by specifying a non-
nilvalue for limit, which says not to search before limit. In this case, the match that is found must begin at or after limit. Here's an example:---------- Buffer: foo ---------- I read "-!-The cat in the hat comes back" twice. ---------- Buffer: foo ---------- (looking-back "read \"" 3) => t (looking-back "read \"" 4) => nilIf greedy is non-
nil, this function extends the match backwards as far as possible, stopping when a single additional previous character cannot be part of a match for regexp. When the match is extended, its starting position is allowed to occur before limit.As a general recommendation, try to avoid using
looking-backwherever possible, since it is slow. For this reason, there are no plans to add alooking-back-pfunction.
This predicate function works like
looking-at, but without updating the match data.
If this variable is non-
nil, it should be a regular expression that says how to search for whitespace. In that case, any group of spaces in a regular expression being searched for stands for use of this regular expression. However, spaces inside of constructs such as `[...]' and `*', `+', `?' are not affected bysearch-spaces-regexp.Since this variable affects all regular expression search and match constructs, you should bind it temporarily for as small as possible a part of the code.
The usual regular expression functions do backtracking when necessary to handle the `\|' and repetition constructs, but they continue this only until they find some match. Then they succeed and report the first match found.
This section describes alternative search functions which perform the full backtracking specified by the POSIX standard for regular expression matching. They continue backtracking until they have tried all possibilities and found all matches, so they can report the longest match, as required by POSIX. This is much slower, so use these functions only when you really need the longest match.
The POSIX search and match functions do not properly support the non-greedy repetition operators (see non-greedy). This is because POSIX backtracking conflicts with the semantics of non-greedy repetition.
This is like
re-search-forwardexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
re-search-backwardexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
looking-atexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
This is like
string-matchexcept that it performs the full backtracking specified by the POSIX standard for regular expression matching.
Emacs keeps track of the start and end positions of the segments of text found during a search; this is called the match data. Thanks to the match data, you can search for a complex pattern, such as a date in a mail message, and then extract parts of the match under control of the pattern.
Because the match data normally describe the most recent search only, you must be careful not to do another search inadvertently between the search you wish to refer back to and the use of the match data. If you can't avoid another intervening search, you must save and restore the match data around it, to prevent it from being overwritten.
Notice that all functions are allowed to overwrite the match data unless they're explicitly documented not to do so. A consequence is that functions that are run implicitly in the background (see Timers, and Idle Timers) should likely save and restore the match data explicitly.
This function replaces all or part of the text matched by the last search. It works by means of the match data.
This function performs a replacement operation on a buffer or string.
If you did the last search in a buffer, you should omit the string argument or specify
nilfor it, and make sure that the current buffer is the one in which you performed the last search. Then this function edits the buffer, replacing the matched text with replacement. It leaves point at the end of the replacement text.If you performed the last search on a string, pass the same string as string. Then this function returns a new string, in which the matched text is replaced by replacement.
If fixedcase is non-
nil, thenreplace-matchuses the replacement text without case conversion; otherwise, it converts the replacement text depending upon the capitalization of the text to be replaced. If the original text is all upper case, this converts the replacement text to upper case. If all words of the original text are capitalized, this capitalizes all the words of the replacement text. If all the words are one-letter and they are all upper case, they are treated as capitalized words rather than all-upper-case words.If literal is non-
nil, then replacement is inserted exactly as it is, the only alterations being case changes as needed. If it isnil(the default), then the character `\' is treated specially. If a `\' appears in replacement, then it must be part of one of the following sequences:
- `\&'
- This stands for the entire text being replaced.
- `\n', where n is a digit
- This stands for the text that matched the nth subexpression in the original regexp. Subexpressions are those expressions grouped inside `\(...\)'. If the nth subexpression never matched, an empty string is substituted.
- `\\'
- This stands for a single `\' in the replacement text.
- `\?'
- This stands for itself (for compatibility with
replace-regexpand related commands; see Regexp Replace).Any other character following `\' signals an error.
The substitutions performed by `\&' and `\n' occur after case conversion, if any. Therefore, the strings they substitute are never case-converted.
If subexp is non-
nil, that says to replace just subexpression number subexp of the regexp that was matched, not the entire match. For example, after matching `foo \(ba*r\)', callingreplace-matchwith 1 as subexp means to replace just the text that matched `\(ba*r\)'.
This function returns the text that would be inserted into the buffer by
replace-match, but without modifying the buffer. It is useful if you want to present the user with actual replacement result, with constructs like `\n' or `\&' substituted with matched groups. Arguments replacement and optional fixedcase, literal, string and subexp have the same meaning as forreplace-match.
This section explains how to use the match data to find out what was matched by the last search or match operation, if it succeeded.
You can ask about the entire matching text, or about a particular parenthetical subexpression of a regular expression. The count argument in the functions below specifies which. If count is zero, you are asking about the entire match. If count is positive, it specifies which subexpression you want.
Recall that the subexpressions of a regular expression are those expressions grouped with escaped parentheses, `\(...\)'. The countth subexpression is found by counting occurrences of `\(' from the beginning of the whole regular expression. The first subexpression is numbered 1, the second 2, and so on. Only regular expressions can have subexpressions—after a simple string search, the only information available is about the entire match.
Every successful search sets the match data. Therefore, you should
query the match data immediately after searching, before calling any
other function that might perform another search. Alternatively, you
may save and restore the match data (see Saving Match Data) around
the call to functions that could perform another search. Or use the
functions that explicitly do not modify the match data;
e.g., string-match-p.
A search which fails may or may not alter the match data. In the current implementation, it does not, but we may change it in the future. Don't try to rely on the value of the match data after a failing search.
This function returns, as a string, the text matched in the last search or match operation. It returns the entire text if count is zero, or just the portion corresponding to the countth parenthetical subexpression, if count is positive.
If the last such operation was done against a string with
string-match, then you should pass the same string as the argument in-string. After a buffer search or match, you should omit in-string or passnilfor it; but you should make sure that the current buffer when you callmatch-stringis the one in which you did the searching or matching. Failure to follow this advice will lead to incorrect results.The value is
nilif count is out of range, or for a subexpression inside a `\|' alternative that wasn't used or a repetition that repeated zero times.
This function is like
match-stringexcept that the result has no text properties.
If the last regular expression search found a match, this function returns the position of the start of the matching text or of a subexpression of it.
If count is zero, then the value is the position of the start of the entire match. Otherwise, count specifies a subexpression in the regular expression, and the value of the function is the starting position of the match for that subexpression.
The value is
nilfor a subexpression inside a `\|' alternative that wasn't used or a repetition that repeated zero times.
This function is like
match-beginningexcept that it returns the position of the end of the match, rather than the position of the beginning.
Here is an example of using the match data, with a comment showing the positions within the text:
(string-match "\\(qu\\)\\(ick\\)"
"The quick fox jumped quickly.")
;0123456789
=> 4
(match-string 0 "The quick fox jumped quickly.")
=> "quick"
(match-string 1 "The quick fox jumped quickly.")
=> "qu"
(match-string 2 "The quick fox jumped quickly.")
=> "ick"
(match-beginning 1) ; The beginning of the match
=> 4 ; with `qu' is at index 4.
(match-beginning 2) ; The beginning of the match
=> 6 ; with `ick' is at index 6.
(match-end 1) ; The end of the match
=> 6 ; with `qu' is at index 6.
(match-end 2) ; The end of the match
=> 9 ; with `ick' is at index 9.
Here is another example. Point is initially located at the beginning of the line. Searching moves point to between the space and the word `in'. The beginning of the entire match is at the 9th character of the buffer (`T'), and the beginning of the match for the first subexpression is at the 13th character (`c').
(list
(re-search-forward "The \\(cat \\)")
(match-beginning 0)
(match-beginning 1))
=> (17 9 13)
---------- Buffer: foo ----------
I read "The cat -!-in the hat comes back" twice.
^ ^
9 13
---------- Buffer: foo ----------
(In this case, the index returned is a buffer position; the first character of the buffer counts as 1.)
The functions match-data and set-match-data read or
write the entire match data, all at once.
This function returns a list of positions (markers or integers) that record all the information on the text that the last search matched. Element zero is the position of the beginning of the match for the whole expression; element one is the position of the end of the match for the expression. The next two elements are the positions of the beginning and end of the match for the first subexpression, and so on. In general, element number 2n corresponds to
(match-beginningn); and element number 2n + 1 corresponds to(match-endn).Normally all the elements are markers or
nil, but if integers is non-nil, that means to use integers instead of markers. (In that case, the buffer itself is appended as an additional element at the end of the list, to facilitate complete restoration of the match data.) If the last match was done on a string withstring-match, then integers are always used, since markers can't point into a string.If reuse is non-
nil, it should be a list. In that case,match-datastores the match data in reuse. That is, reuse is destructively modified. reuse does not need to have the right length. If it is not long enough to contain the match data, it is extended. If it is too long, the length of reuse stays the same, but the elements that were not used are set tonil. The purpose of this feature is to reduce the need for garbage collection.If reseat is non-
nil, all markers on the reuse list are reseated to point to nowhere.As always, there must be no possibility of intervening searches between the call to a search function and the call to
match-datathat is intended to access the match data for that search.(match-data) => (#<marker at 9 in foo> #<marker at 17 in foo> #<marker at 13 in foo> #<marker at 17 in foo>)
This function sets the match data from the elements of match-list, which should be a list that was the value of a previous call to
match-data. (More precisely, anything that has the same format will work.)If match-list refers to a buffer that doesn't exist, you don't get an error; that sets the match data in a meaningless but harmless way.
If reseat is non-
nil, all markers on the match-list list are reseated to point to nowhere.
store-match-datais a semi-obsolete alias forset-match-data.
When you call a function that may search, you may need to save and restore the match data around that call, if you want to preserve the match data from an earlier search for later use. Here is an example that shows the problem that arises if you fail to save the match data:
(re-search-forward "The \\(cat \\)")
=> 48
(foo) ; foo does more searching.
(match-end 0)
=> 61 ; Unexpected result---not 48!
You can save and restore the match data with save-match-data:
This macro executes body, saving and restoring the match data around it. The return value is the value of the last form in body.
You could use set-match-data together with match-data to
imitate the effect of the special form save-match-data. Here is
how:
(let ((data (match-data)))
(unwind-protect
... ; Ok to change the original match data.
(set-match-data data)))
Emacs automatically saves and restores the match data when it runs process filter functions (see Filter Functions) and process sentinels (see Sentinels).
If you want to find all matches for a regexp in part of the buffer,
and replace them, the best way is to write an explicit loop using
re-search-forward and replace-match, like this:
(while (re-search-forward "foo[ \t]+bar" nil t)
(replace-match "foobar"))
See Replacing the Text that Matched, for a
description of replace-match.
However, replacing matches in a string is more complex, especially if you want to do it efficiently. So Emacs provides a function to do this.
This function copies string and searches it for matches for regexp, and replaces them with rep. It returns the modified copy. If start is non-
nil, the search for matches starts at that index in string, so matches starting before that index are not changed.This function uses
replace-matchto do the replacement, and it passes the optional arguments fixedcase, literal and subexp along toreplace-match.Instead of a string, rep can be a function. In that case,
replace-regexp-in-stringcalls rep for each match, passing the text of the match as its sole argument. It collects the value rep returns and passes that toreplace-matchas the replacement string. The match data at this point are the result of matching regexp against a substring of string.
If you want to write a command along the lines of query-replace,
you can use perform-replace to do the work.
This function is the guts of
query-replaceand related commands. It searches for occurrences of from-string in the text between positions start and end and replaces some or all of them. If start isnil(or omitted), point is used instead, and the end of the buffer's accessible portion is used for end.If query-flag is
nil, it replaces all occurrences; otherwise, it asks the user what to do about each one.If regexp-flag is non-
nil, then from-string is considered a regular expression; otherwise, it must match literally. If delimited-flag is non-nil, then only replacements surrounded by word boundaries are considered.The argument replacements specifies what to replace occurrences with. If it is a string, that string is used. It can also be a list of strings, to be used in cyclic order.
If replacements is a cons cell,
(function.data), this means to call function after each match to get the replacement text. This function is called with two arguments: data, and the number of replacements already made.If repeat-count is non-
nil, it should be an integer. Then it specifies how many times to use each of the strings in the replacements list before advancing cyclically to the next one.If from-string contains upper-case letters, then
perform-replacebindscase-fold-searchtonil, and it uses the replacements without altering their case.Normally, the keymap
query-replace-mapdefines the possible user responses for queries. The argument map, if non-nil, specifies a keymap to use instead ofquery-replace-map.This function uses one of two functions to search for the next occurrence of from-string. These functions are specified by the values of two variables:
replace-re-search-functionandreplace-search-function. The former is called when the argument regexp-flag is non-nil, the latter when it isnil.
This variable holds a special keymap that defines the valid user responses for
perform-replaceand the commands that use it, as well asy-or-n-pandmap-y-or-n-p. This map is unusual in two ways:
- The key bindings are not commands, just symbols that are meaningful to the functions that use this map.
- Prefix keys are not supported; each key binding must be for a single-event key sequence. This is because the functions don't use
read-key-sequenceto get the input; instead, they read a single event and look it up “by hand”.
Here are the meaningful bindings for query-replace-map.
Several of them are meaningful only for query-replace and
friends.
actskipexitexit-prefixexit, but add the key that was pressed to
unread-command-events (see Event Input Misc).
act-and-exitact-and-showautomaticbackupeditedit-replacementdelete-and-editrecenterscroll-upscroll-downscroll-other-windowscroll-other-window-downy-or-n-p and related functions use this
answer.
quity-or-n-p and related functions
use this answer.
helpThis variable holds a keymap that extends
query-replace-mapby providing additional keybindings that are useful in multi-buffer replacements. The additional bindings are:
automatic-all- Answer this question and all subsequent questions in the series with “yes”, without further user interaction, for all remaining buffers.
exit-current- Answer this question “no”, and give up on the entire series of questions for the current buffer. Continue to the next buffer in the sequence.
This variable specifies a function that
perform-replacecalls to search for the next string to replace. Its default value issearch-forward. Any other value should name a function of 3 arguments: the first 3 arguments ofsearch-forward(see String Search).
This variable specifies a function that
perform-replacecalls to search for the next regexp to replace. Its default value isre-search-forward. Any other value should name a function of 3 arguments: the first 3 arguments ofre-search-forward(see Regexp Search).
This section describes some variables that hold regular expressions used for certain purposes in editing:
This is the regular expression describing line-beginnings that separate pages. The default value is
"^\014"(i.e.,"^^L"or"^\C-l"); this matches a line that starts with a formfeed character.
The following two regular expressions should not assume the match always starts at the beginning of a line; they should not use `^' to anchor the match. Most often, the paragraph commands do check for a match only at the beginning of a line, which means that `^' would be superfluous. When there is a nonzero left margin, they accept matches that start after the left margin. In that case, a `^' would be incorrect. However, a `^' is harmless in modes where a left margin is never used.
This is the regular expression for recognizing the beginning of a line that separates paragraphs. (If you change this, you may have to change
paragraph-startalso.) The default value is"[ \t\f]*$", which matches a line that consists entirely of spaces, tabs, and form feeds (after its left margin).
This is the regular expression for recognizing the beginning of a line that starts or separates paragraphs. The default value is
"\f\\|[ \t]*$", which matches a line containing only whitespace or starting with a form feed (after its left margin).
If non-
nil, the value should be a regular expression describing the end of a sentence, including the whitespace following the sentence. (All paragraph boundaries also end sentences, regardless.)If the value is
nil, as it is by default, then the functionsentence-endconstructs the regexp. That is why you should always call the functionsentence-endto obtain the regexp to be used to recognize the end of a sentence.
This function returns the value of the variable
sentence-end, if non-nil. Otherwise it returns a default value based on the values of the variablessentence-end-double-space(see Definition of sentence-end-double-space),sentence-end-without-period, andsentence-end-without-space.
A syntax table specifies the syntactic role of each character in a buffer. It can be used to determine where words, symbols, and other syntactic constructs begin and end. This information is used by many Emacs facilities, including Font Lock mode (see Font Lock Mode) and the various complex movement commands (see Motion).
A syntax table is a data structure which can be used to look up the syntax class and other syntactic properties of each character. Syntax tables are used by Lisp programs for scanning and moving across text.
Internally, a syntax table is a char-table (see Char-Tables).
The element at index c describes the character with code
c; its value is a cons cell which specifies the syntax of the
character in question. See Syntax Table Internals, for details.
However, instead of using aset and aref to modify and
inspect syntax table contents, you should usually use the higher-level
functions char-syntax and modify-syntax-entry, which are
described in Syntax Table Functions.
Each buffer has its own major mode, and each major mode has its own
idea of the syntax class of various characters. For example, in Lisp
mode, the character `;' begins a comment, but in C mode, it
terminates a statement. To support these variations, the syntax table
is local to each buffer. Typically, each major mode has its own
syntax table, which it installs in all buffers that use that mode.
For example, the variable emacs-lisp-mode-syntax-table holds
the syntax table used by Emacs Lisp mode, and
c-mode-syntax-table holds the syntax table used by C mode.
Changing a major mode's syntax table alters the syntax in all of that
mode's buffers, as well as in any buffers subsequently put in that
mode. Occasionally, several similar modes share one syntax table.
See Example Major Modes, for an example of how to set up a syntax
table.
A syntax table can inherit from another syntax table, which is called its parent syntax table. A syntax table can leave the syntax class of some characters unspecified, by giving them the “inherit” syntax class; such a character then acquires the syntax class specified by the parent syntax table (see Syntax Class Table). Emacs defines a standard syntax table, which is the default parent syntax table, and is also the syntax table used by Fundamental mode.
This function returns the standard syntax table, which is the syntax table used in Fundamental mode.
Syntax tables are not used by the Emacs Lisp reader, which has its own built-in syntactic rules which cannot be changed. (Some Lisp systems provide ways to redefine the read syntax, but we decided to leave this feature out of Emacs Lisp for simplicity.)
The syntax class of a character describes its syntactic role. Each syntax table specifies the syntax class of each character. There is no necessary relationship between the class of a character in one syntax table and its class in any other table.
Each syntax class is designated by a mnemonic character, which serves as the name of the class when you need to specify a class. Usually, this designator character is one that is often assigned that class; however, its meaning as a designator is unvarying and independent of what syntax that character currently has. Thus, `\' as a designator character always stands for escape character syntax, regardless of whether the `\' character actually has that syntax in the current syntax table. See Syntax Class Table, for a list of syntax classes and their designator characters.
A syntax descriptor is a Lisp string that describes the syntax
class and other syntactic properties of a character. When you want to
modify the syntax of a character, that is done by calling the function
modify-syntax-entry and passing a syntax descriptor as one of
its arguments (see Syntax Table Functions).
The first character in a syntax descriptor must be a syntax class designator character. The second character, if present, specifies a matching character (e.g., in Lisp, the matching character for `(' is `)'); a space specifies that there is no matching character. Then come characters specifying additional syntax properties (see Syntax Flags).
If no matching character or flags are needed, only one character (specifying the syntax class) is sufficient.
For example, the syntax descriptor for the character `*' in C
mode is ". 23" (i.e., punctuation, matching character slot
unused, second character of a comment-starter, first character of a
comment-ender), and the entry for `/' is `. 14' (i.e.,
punctuation, matching character slot unused, first character of a
comment-starter, second character of a comment-ender).
Emacs also defines raw syntax descriptors, which are used to describe syntax classes at a lower level. See Syntax Table Internals.
Here is a table of syntax classes, the characters that designate them, their meanings, and examples of their use.
This syntax class can be designated by either ` ' or
`-'. Both designators are equivalent.
In human languages, and in C code, the parenthesis pairs are
`()', `[]', and `{}'. In Emacs Lisp, the delimiters
for lists and vectors (`()' and `[]') are classified as
parenthesis characters.
The parsing facilities of Emacs consider a string as a single token. The usual syntactic meanings of the characters in the string are suppressed.
The Lisp modes have two string quote characters: double-quote (`"') and vertical bar (`|'). `|' is not used in Emacs Lisp, but it is used in Common Lisp. C also has two string quote characters: double-quote for strings, and apostrophe (`'') for character constants.
Human text has no string quote characters. We do not want quotation
marks to turn off the usual syntactic properties of other characters
in the quotation.
Characters in this class count as part of words if
words-include-escapes is non-nil. See Word Motion.
Characters in this class count as part of words if
words-include-escapes is non-nil. See Word Motion.
This class is used for backslash in TeX mode.
This syntax class is primarily meant for use with the
syntax-table text property (see Syntax Properties). You
can mark any range of characters as forming a comment, by giving the
first and last characters of the range syntax-table properties
identifying them as generic comment delimiters.
This syntax class is primarily meant for use with the
syntax-table text property (see Syntax Properties). You
can mark any range of characters as forming a string constant, by
giving the first and last characters of the range syntax-table
properties identifying them as generic string delimiters.
In addition to the classes, entries for characters in a syntax table can specify flags. There are eight possible flags, represented by the characters `1', `2', `3', `4', `b', `c', `n', and `p'.
All the flags except `p' are used to describe comment delimiters. The digit flags are used for comment delimiters made up of 2 characters. They indicate that a character can also be part of a comment sequence, in addition to the syntactic properties associated with its character class. The flags are independent of the class and each other for the sake of characters such as `*' in C mode, which is a punctuation character, and the second character of a start-of-comment sequence (`/*'), and the first character of an end-of-comment sequence (`*/'). The flags `b', `c', and `n' are used to qualify the corresponding comment delimiter.
Here is a table of the possible flags for a character c, and what they mean:
Emacs supports several comment styles simultaneously in any one syntax table. A comment style is a set of flags `b', `c', and `n', so there can be up to 8 different comment styles. Each comment delimiter has a style and only matches comment delimiters of the same style. Thus if a comment starts with the comment-start sequence of style “bn”, it will extend until the next matching comment-end sequence of style “bn”.
The appropriate comment syntax settings for C++ can be as follows:
This defines four comment-delimiting sequences:
The function backward-prefix-chars moves back over these
characters, as well as over characters whose primary syntax class is
prefix (`''). See Motion and Syntax.
In this section we describe functions for creating, accessing and altering syntax tables.
This function creates a new syntax table. If table is non-
nil, the parent of the new syntax table is table; otherwise, the parent is the standard syntax table.In the new syntax table, all characters are initially given the “inherit” (`@') syntax class, i.e., their syntax is inherited from the parent table (see Syntax Class Table).
This function constructs a copy of table and returns it. If table is omitted or
nil, it returns a copy of the standard syntax table. Otherwise, an error is signaled if table is not a syntax table.
This function sets the syntax entry for char according to syntax-descriptor. char must be a character, or a cons cell of the form
(min.max); in the latter case, the function sets the syntax entries for all characters in the range between min and max, inclusive.The syntax is changed only for table, which defaults to the current buffer's syntax table, and not in any other syntax table.
The argument syntax-descriptor is a syntax descriptor, i.e., a string whose first character is a syntax class designator and whose second and subsequent characters optionally specify a matching character and syntax flags. See Syntax Descriptors. An error is signaled if syntax-descriptor is not a valid syntax descriptor.
This function always returns
nil. The old syntax information in the table for this character is discarded.
Examples:
;; Put the space character in class whitespace. (modify-syntax-entry ?\s " ") => nil ;; Make `$' an open parenthesis character, ;; with `^' as its matching close. (modify-syntax-entry ?$ "(^") => nil ;; Make `^' a close parenthesis character, ;; with `$' as its matching open. (modify-syntax-entry ?^ ")$") => nil ;; Make `/' a punctuation character, ;; the first character of a start-comment sequence, ;; and the second character of an end-comment sequence. ;; This is used in C mode. (modify-syntax-entry ?/ ". 14") => nil
This function returns the syntax class of character, represented by its designator character (see Syntax Class Table). This returns only the class, not its matching character or syntax flags.
The following examples apply to C mode. (We use
stringto make it easier to see the character returned bychar-syntax.);; Space characters have whitespace syntax class. (string (char-syntax ?\s)) => " " ;; Forward slash characters have punctuation syntax. ;; Note that thischar-syntaxcall does not reveal ;; that it is also part of comment-start and -end sequences. (string (char-syntax ?/)) => "." ;; Open parenthesis characters have open parenthesis syntax. ;; Note that thischar-syntaxcall does not reveal that ;; it has a matching character, `)'. (string (char-syntax ?\()) => "("
This function makes table the syntax table for the current buffer. It returns table.
This function returns the current syntax table, which is the table for the current buffer.
This command displays the contents of the syntax table of buffer (by default, the current buffer) in a help buffer.
This macro executes body using table as the current syntax table. It returns the value of the last form in body, after restoring the old current syntax table.
Since each buffer has its own current syntax table, we should make that more precise:
with-syntax-tabletemporarily alters the current syntax table of whichever buffer is current at the time the macro execution starts. Other buffers are not affected.
When the syntax table is not flexible enough to specify the syntax of
a language, you can override the syntax table for specific character
occurrences in the buffer, by applying a syntax-table text
property. See Text Properties, for how to apply text properties.
The valid values of syntax-table text property are:
(syntax-code . matching-char)
nilnil, the character's syntax is determined from
the current syntax table in the usual way.
If this is non-
nil, the syntax scanning functions, likeforward-sexp, pay attention to syntax text properties. Otherwise they use only the current syntax table.
This variable, if non-
nil, should store a function for applyingsyntax-tableproperties to a specified stretch of text. It is intended to be used by major modes to install a function which appliessyntax-tableproperties in some mode-appropriate way.The function is called by
syntax-ppss(see Position Parse), and by Font Lock mode during syntactic fontification (see Syntactic Font Lock). It is called with two arguments, start and end, which are the starting and ending positions of the text on which it should act. It is allowed to callsyntax-ppsson any position before end. However, it should not callsyntax-ppss-flush-cache; so, it is not allowed to callsyntax-ppsson some position and later modify the buffer at an earlier position.
This abnormal hook is run by the syntax parsing code prior to calling
syntax-propertize-function. Its role is to help locate safe starting and ending buffer positions for passing tosyntax-propertize-function. For example, a major mode can add a function to this hook to identify multi-line syntactic constructs, and ensure that the boundaries do not fall in the middle of one.Each function in this hook should accept two arguments, start and end. It should return either a cons cell of two adjusted buffer positions,
(new-start.new-end), ornilif no adjustment is necessary. The hook functions are run in turn, repeatedly, until they all returnnil.
This section describes functions for moving across characters that have certain syntax classes.
This function moves point forward across characters having syntax classes mentioned in syntaxes (a string of syntax class characters). It stops when it encounters the end of the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with `^', then the function skips characters whose syntax is not in syntaxes.
The return value is the distance traveled, which is a nonnegative integer.
This function moves point backward across characters whose syntax classes are mentioned in syntaxes. It stops when it encounters the beginning of the buffer, or position limit (if specified), or a character it is not supposed to skip.
If syntaxes starts with `^', then the function skips characters whose syntax is not in syntaxes.
The return value indicates the distance traveled. It is an integer that is zero or less.
This function moves point backward over any number of characters with expression prefix syntax. This includes both characters in the expression prefix syntax class, and characters with the `p' flag.
This section describes functions for parsing and scanning balanced expressions. We will refer to such expressions as sexps, following the terminology of Lisp, even though these functions can act on languages other than Lisp. Basically, a sexp is either a balanced parenthetical grouping, a string, or a symbol (i.e., a sequence of characters whose syntax is either word constituent or symbol constituent). However, characters in the expression prefix syntax class (see Syntax Class Table) are treated as part of the sexp if they appear next to it.
The syntax table controls the interpretation of characters, so these functions can be used for Lisp expressions when in Lisp mode and for C expressions when in C mode. See List Motion, for convenient higher-level functions for moving over balanced expressions.
A character's syntax controls how it changes the state of the parser, rather than describing the state itself. For example, a string delimiter character toggles the parser state between in-string and in-code, but the syntax of characters does not directly say whether they are inside a string. For example (note that 15 is the syntax code for generic string delimiters),
(put-text-property 1 9 'syntax-table '(15 . nil))
does not tell Emacs that the first eight chars of the current buffer are a string, but rather that they are all string delimiters. As a result, Emacs treats them as four consecutive empty string constants.
This section describes simple point-motion functions that operate based on parsing expressions.
This function scans forward count balanced parenthetical groupings from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.
If depth is nonzero, treat the starting position as being depth parentheses deep. The scanner moves forward or backward through the buffer until the depth changes to zero count times. Hence, a positive value for depth has the effect of moving out depth levels of parenthesis from the starting position, while a negative depth has the effect of moving deeper by -depth levels of parenthesis.
Scanning ignores comments if
parse-sexp-ignore-commentsis non-nil.If the scan reaches the beginning or end of the accessible part of the buffer before it has scanned over count parenthetical groupings, the return value is
nilif the depth at that point is zero; if the depth is non-zero, ascan-errorerror is signaled.
This function scans forward count sexps from position from. It returns the position where the scan stops. If count is negative, the scan moves backwards.
Scanning ignores comments if
parse-sexp-ignore-commentsis non-nil.If the scan reaches the beginning or end of (the accessible part of) the buffer while in the middle of a parenthetical grouping, an error is signaled. If it reaches the beginning or end between groupings but before count is used up,
nilis returned.
This function moves point forward across count complete comments (that is, including the starting delimiter and the terminating delimiter if any), plus any whitespace encountered on the way. It moves backward if count is negative. If it encounters anything other than a comment or whitespace, it stops, leaving point at the place where it stopped. This includes (for instance) finding the end of a comment when moving forward and expecting the beginning of one. The function also stops immediately after moving over the specified number of complete comments. If count comments are found as expected, with nothing except whitespace between them, it returns
t; otherwise it returnsnil.This function cannot tell whether the comments it traverses are embedded within a string. If they look like comments, it treats them as comments.
To move forward over all comments and whitespace following point, use
(forward-comment (buffer-size)).(buffer-size)is a good argument to use, because the number of comments in the buffer cannot exceed that many.
For syntactic analysis, such as in indentation, often the useful thing is to compute the syntactic state corresponding to a given buffer position. This function does that conveniently.
This function returns the parser state that the parser would reach at position pos starting from the beginning of the buffer. See Parser State, for a description of the parser state.
The return value is the same as if you call the low-level parsing function
parse-partial-sexpto parse from the beginning of the buffer to pos (see Low-Level Parsing). However,syntax-ppssuses a cache to speed up the computation. Due to this optimization, the second value (previous complete subexpression) and sixth value (minimum parenthesis depth) in the returned parser state are not meaningful.This function has a side effect: it adds a buffer-local entry to
before-change-functions(see Change Hooks) forsyntax-ppss-flush-cache(see below). This entry keeps the cache consistent as the buffer is modified. However, the cache might not be updated ifsyntax-ppssis called whilebefore-change-functionsis temporarily let-bound, or if the buffer is modified without running the hook, such as when usinginhibit-modification-hooks. In those cases, it is necessary to callsyntax-ppss-flush-cacheexplicitly.
This function flushes the cache used by
syntax-ppss, starting at position beg. The remaining arguments, ignored-args, are ignored; this function accepts them so that it can be directly used on hooks such asbefore-change-functions(see Change Hooks).
A parser state is a list of ten elements describing the state
of the syntactic parser, after it parses the text between a specified
starting point and a specified end point in the buffer. Parsing
functions such as syntax-ppss
(see Position Parse)
return a parser state as the value. Some parsing functions accept a
parser state as an argument, for resuming parsing.
Here are the meanings of the elements of the parser state:
nil if none.
nil if none.
nil if inside a string. More precisely, this is the
character that will terminate the string, or t if a generic
string delimiter character should terminate it.
t if inside a non-nestable comment (of any comment style;
see Syntax Flags); or the comment nesting level if inside a
comment that can be nested.
t if the end point is just after a quote character.
nil if not in a comment or in a
comment of style `a'; 1 for a comment of style `b'; 2 for a
comment of style `c'; and syntax-table for a comment that
should be ended by a generic comment delimiter character.
nil.
Elements 1, 2, and 6 are ignored in a state which you pass as an argument to continue parsing, and elements 8 and 9 are used only in trivial cases. Those elements are mainly used internally by the parser code.
One additional piece of useful information is available from a parser state using this function:
This function extracts, from parser state state, the last position scanned in the parse which was at top level in grammatical structure. “At top level” means outside of any parentheses, comments, or strings.
The value is
nilif state represents a parse which has arrived at a top level position.
The most basic way to use the expression parser is to tell it to start at a given position with a certain state, and parse up to a specified end position.
This function parses a sexp in the current buffer starting at start, not scanning past limit. It stops at position limit or when certain criteria described below are met, and sets point to the location where parsing stops. It returns a parser state describing the status of the parse at the point where it stops.
If the third argument target-depth is non-
nil, parsing stops if the depth in parentheses becomes equal to target-depth. The depth starts at 0, or at whatever is given in state.If the fourth argument stop-before is non-
nil, parsing stops when it comes to any character that starts a sexp. If stop-comment is non-nil, parsing stops when it comes to the start of a comment. If stop-comment is the symbolsyntax-table, parsing stops after the start of a comment or a string, or the end of a comment or a string, whichever comes first.If state is
nil, start is assumed to be at the top level of parenthesis structure, such as the beginning of a function definition. Alternatively, you might wish to resume parsing in the middle of the structure. To do this, you must provide a state argument that describes the initial status of parsing. The value returned by a previous call toparse-partial-sexpwill do nicely.
If this variable is non-
nil,scan-sexpstreats all non-ASCII characters as symbol constituents regardless of what the syntax table says about them. (However, text properties can still override the syntax.)
If the value is non-
nil, then comments are treated as whitespace by the functions in this section and byforward-sexp,scan-listsandscan-sexps.
The behavior of parse-partial-sexp is also affected by
parse-sexp-lookup-properties (see Syntax Properties).
If this buffer local variable is non-
nil, a single character which usually terminates a comment doesn't do so when that character is escaped. This is used in C and C++ Modes, where line comments starting with `//' can be continued onto the next line by escaping the newline with `\'.
You can use forward-comment to move forward or backward over
one comment or several comments.
Syntax tables are implemented as char-tables (see Char-Tables), but most Lisp programs don't work directly with their elements. Syntax tables do not store syntax data as syntax descriptors (see Syntax Descriptors); they use an internal format, which is documented in this section. This internal format can also be assigned as syntax properties (see Syntax Properties).
Each entry in a syntax table is a raw syntax descriptor: a
cons cell of the form (syntax-code
. matching-char). syntax-code is an integer which
encodes the syntax class and syntax flags, according to the table
below. matching-char, if non-nil, specifies a matching
character (similar to the second character in a syntax descriptor).
Here are the syntax codes corresponding to the various syntax classes:
| Code | Class | Code |
Class
|
| 0 | whitespace | 8 | paired delimiter
|
| 1 | punctuation | 9 | escape
|
| 2 | word | 10 | character quote
|
| 3 | symbol | 11 | comment-start
|
| 4 | open parenthesis | 12 | comment-end
|
| 5 | close parenthesis | 13 | inherit
|
| 6 | expression prefix | 14 | generic comment
|
| 7 | string quote | 15 | generic string
|
For example, in the standard syntax table, the entry for `(' is
(4 . 41). 41 is the character code for `)'.
Syntax flags are encoded in higher order bits, starting 16 bits from the least significant bit. This table gives the power of two which corresponds to each syntax flag.
| Prefix | Flag | Prefix |
Flag
|
| `1' |
(lsh 1 16) |
`p' |
(lsh 1 20)
|
| `2' |
(lsh 1 17) |
`b' |
(lsh 1 21)
|
| `3' |
(lsh 1 18) |
`n' |
(lsh 1 22)
|
| `4' |
(lsh 1 19)
|
Given a syntax descriptor desc (a string), this function returns the corresponding raw syntax descriptor.
This function returns the raw syntax descriptor for the character in the buffer after position pos, taking account of syntax properties as well as the syntax table. If pos is outside the buffer's accessible portion (see accessible portion), the return value is
nil.
This function returns the syntax code for the raw syntax descriptor syntax. More precisely, it takes the raw syntax descriptor's syntax-code component, masks off the high 16 bits which record the syntax flags, and returns the resulting integer.
If syntax is
nil, the return value is returnsnil. This is so that the expression(syntax-class (syntax-after pos))evaluates to
nilifposis outside the buffer's accessible portion, without throwing errors or returning an incorrect code.
Categories provide an alternate way of classifying characters syntactically. You can define several categories as needed, then independently assign each character to one or more categories. Unlike syntax classes, categories are not mutually exclusive; it is normal for one character to belong to several categories.
Each buffer has a category table which records which categories are defined and also which characters belong to each category. Each category table defines its own categories, but normally these are initialized by copying from the standard categories table, so that the standard categories are available in all modes.
Each category has a name, which is an ASCII printing character in
the range ` ' to `~'. You specify the name of a category
when you define it with define-category.
The category table is actually a char-table (see Char-Tables).
The element of the category table at index c is a category
set—a bool-vector—that indicates which categories character c
belongs to. In this category set, if the element at index cat is
t, that means category cat is a member of the set, and that
character c belongs to category cat.
For the next three functions, the optional argument table defaults to the current buffer's category table.
This function defines a new category, with name char and documentation docstring, for the category table table.
Here's an example of defining a new category for characters that have strong right-to-left directionality (see Bidirectional Display) and using it in a special category table. To obtain the information about the directionality of characters, the example code uses the `bidi-class' Unicode property (see bidi-class).
(defvar special-category-table-for-bidi ;; Make an empty category-table. (let ((category-table (make-category-table)) ;; Create a char-table which gives the 'bidi-class' Unicode ;; property for each character. (uniprop-table (unicode-property-table-internal 'bidi-class))) (define-category ?R "Characters of bidi-class R, AL, or RLO" category-table) ;; Modify the category entry of each character whose 'bidi-class' ;; Unicode property is R, AL, or RLO -- these have a ;; right-to-left directionality. (map-char-table #'(lambda (key val) (if (memq val '(R AL RLO)) (modify-category-entry key ?R category-table))) uniprop-table) category-table))
This function returns the documentation string of category category in category table table.
(category-docstring ?a) => "ASCII" (category-docstring ?l) => "Latin"
This function returns a category name (a character) which is not currently defined in table. If all possible categories are in use in table, it returns
nil.
This function returns
tif object is a category table, otherwisenil.
This function constructs a copy of table and returns it. If table is not supplied (or is
nil), it returns a copy of the standard category table. Otherwise, an error is signaled if table is not a category table.
This function makes table the category table for the current buffer. It returns table.
This creates and returns an empty category table. In an empty category table, no categories have been allocated, and no characters belong to any categories.
This function returns a new category set—a bool-vector—whose initial contents are the categories listed in the string categories. The elements of categories should be category names; the new category set has
tfor each of those categories, andnilfor all other categories.(make-category-set "al") => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function returns the category set for character char in the current buffer's category table. This is the bool-vector which records which categories the character char belongs to. The function
char-category-setdoes not allocate storage, because it returns the same bool-vector that exists in the category table.(char-category-set ?a) => #&128"\0\0\0\0\0\0\0\0\0\0\0\0\2\20\0\0"
This function converts the category set category-set into a string containing the characters that designate the categories that are members of the set.
(category-set-mnemonics (char-category-set ?a)) => "al"
This function modifies the category set of char in category table table (which defaults to the current buffer's category table). char can be a character, or a cons cell of the form
(min.max); in the latter case, the function modifies the category sets of all characters in the range between min and max, inclusive.Normally, it modifies a category set by adding category to it. But if reset is non-
nil, then it deletes category instead.
This function describes the category specifications in the current category table. It inserts the descriptions in a buffer, and then displays that buffer. If buffer-or-name is non-
nil, it describes the category table of that buffer instead.
An abbreviation or abbrev is a string of characters that may be expanded to a longer string. The user can insert the abbrev string and find it replaced automatically with the expansion of the abbrev. This saves typing.
The set of abbrevs currently in effect is recorded in an abbrev table. Each buffer has a local abbrev table, but normally all buffers in the same major mode share one abbrev table. There is also a global abbrev table. Normally both are used.
An abbrev table is represented as an obarray. See Creating Symbols, for information about obarrays. Each abbreviation is represented by a symbol in the obarray. The symbol's name is the abbreviation; its value is the expansion; its function definition is the hook function for performing the expansion (see Defining Abbrevs); and its property list cell contains various additional properties, including the use count and the number of times the abbreviation has been expanded (see Abbrev Properties).
Certain abbrevs, called system abbrevs, are defined by a major
mode instead of the user. A system abbrev is identified by its
non-nil :system property (see Abbrev Properties).
When abbrevs are saved to an abbrev file, system abbrevs are omitted.
See Abbrev Files.
Because the symbols used for abbrevs are not interned in the usual obarray, they will never appear as the result of reading a Lisp expression; in fact, normally they are never used except by the code that handles abbrevs. Therefore, it is safe to use them in a nonstandard way.
If the minor mode Abbrev mode is enabled, the buffer-local variable
abbrev-mode is non-nil, and abbrevs are automatically
expanded in the buffer. For the user-level commands for abbrevs, see
Abbrev Mode.
This section describes how to create and manipulate abbrev tables.
This function creates and returns a new, empty abbrev table—an obarray containing no symbols. It is a vector filled with zeros. props is a property list that is applied to the new table (see Abbrev Table Properties).
This function returns a non-
nilvalue if object is an abbrev table.
This function undefines all the abbrevs in abbrev-table, leaving it empty.
This function returns a copy of abbrev-table—a new abbrev table containing the same abbrev definitions. It does not copy any property lists; only the names, values, and functions.
This function defines tabname (a symbol) as an abbrev table name, i.e., as a variable whose value is an abbrev table. It defines abbrevs in the table according to definitions, a list of elements of the form
(abbrevname expansion[hook] [props...]). These elements are passed as arguments todefine-abbrev.The optional string docstring is the documentation string of the variable tabname. The property list props is applied to the abbrev table (see Abbrev Table Properties).
If this function is called more than once for the same tabname, subsequent calls add the definitions in definitions to tabname, rather than overwriting the entire original contents. (A subsequent call only overrides abbrevs explicitly redefined or undefined in definitions.)
This is a list of symbols whose values are abbrev tables.
define-abbrev-tableadds the new abbrev table name to this list.
This function inserts before point a description of the abbrev table named name. The argument name is a symbol whose value is an abbrev table.
If human is non-
nil, the description is human-oriented. System abbrevs are listed and identified as such. Otherwise the description is a Lisp expression—a call todefine-abbrev-tablethat would define name as it is currently defined, but without the system abbrevs. (The mode or package using name is supposed to add these to name separately.)
define-abbrev is the low-level basic function for defining an
abbrev in an abbrev table.
When a major mode defines a system abbrev, it should call
define-abbrev and specify t for the :system
property. Be aware that any saved non-system abbrevs are restored
at startup, i.e., before some major modes are loaded. Therefore, major
modes should not assume that their abbrev tables are empty when they
are first loaded.
This function defines an abbrev named name, in abbrev-table, to expand to expansion and call hook, with properties props (see Abbrev Properties). The return value is name. The
:systemproperty in props is treated specially here: if it has the valueforce, then it will overwrite an existing definition even for a non-system abbrev of the same name.name should be a string. The argument expansion is normally the desired expansion (a string), or
nilto undefine the abbrev. If it is anything but a string ornil, then the abbreviation expands solely by running hook.The argument hook is a function or
nil. If hook is non-nil, then it is called with no arguments after the abbrev is replaced with expansion; point is located at the end of expansion when hook is called.If hook is a non-
nilsymbol whoseno-self-insertproperty is non-nil, hook can explicitly control whether to insert the self-inserting input character that triggered the expansion. If hook returns non-nilin this case, that inhibits insertion of the character. By contrast, if hook returnsnil,expand-abbrev(orabbrev-insert) also returnsnil, as if expansion had not really occurred.Normally,
define-abbrevsets the variableabbrevs-changedtot, if it actually changes the abbrev. This is so that some commands will offer to save the abbrevs. It does not do this for a system abbrev, since those aren't saved anyway.
If this variable is non-
nil, it means that the user plans to use global abbrevs only. This tells the commands that define mode-specific abbrevs to define global ones instead. This variable does not alter the behavior of the functions in this section; it is examined by their callers.
A file of saved abbrev definitions is actually a file of Lisp code.
The abbrevs are saved in the form of a Lisp program to define the same
abbrev tables with the same contents. Therefore, you can load the file
with load (see How Programs Do Loading). However, the
function quietly-read-abbrev-file is provided as a more
convenient interface. Emacs automatically calls this function at
startup.
User-level facilities such as save-some-buffers can save
abbrevs in a file automatically, under the control of variables
described here.
This is the default file name for reading and saving abbrevs. By default, Emacs will look for ~/.emacs.d/abbrev_defs, and, if not found, for ~/.abbrev_defs; if neither file exists, Emacs will create ~/.emacs.d/abbrev_defs.
This function reads abbrev definitions from a file named filename, previously written with
write-abbrev-file. If filename is omitted ornil, the file specified inabbrev-file-nameis used.As the name implies, this function does not display any messages.
A non-
nilvalue forsave-abbrevsmeans that Emacs should offer to save abbrevs (if any have changed) when files are saved. If the value issilently, Emacs saves the abbrevs without asking the user.abbrev-file-namespecifies the file to save the abbrevs in. The default value ist.
This variable is set non-
nilby defining or altering any abbrevs (except system abbrevs). This serves as a flag for various Emacs commands to offer to save your abbrevs.
Save all abbrev definitions (except system abbrevs), for all abbrev tables listed in
abbrev-table-name-list, in the file filename, in the form of a Lisp program that when loaded will define the same abbrevs. If filename isnilor omitted,abbrev-file-nameis used. This function returnsnil.
Abbrevs are usually expanded by certain interactive commands,
including self-insert-command. This section describes the
subroutines used in writing such commands, as well as the variables they
use for communication.
This function returns the symbol representing the abbrev named abbrev. It returns
nilif that abbrev is not defined. The optional second argument table is the abbrev table in which to look it up. If table isnil, this function tries first the current buffer's local abbrev table, and second the global abbrev table.
This function returns the string that abbrev would expand into (as defined by the abbrev tables used for the current buffer). It returns
nilif abbrev is not a valid abbrev. The optional argument table specifies the abbrev table to use, as inabbrev-symbol.
This command expands the abbrev before point, if any. If point does not follow an abbrev, this command does nothing. To do the expansion, it calls the function that is the value of the
abbrev-expand-functionvariable, with no arguments, and returns whatever that function does.The default expansion function returns the abbrev symbol if it did expansion, and
nilotherwise. If the abbrev symbol has a hook function that is a symbol whoseno-self-insertproperty is non-nil, and if the hook function returnsnilas its value, then the default expansion function returnsnil, even though expansion did occur.
This function inserts the abbrev expansion of
abbrev, replacing the text betweenstartandend. Ifstartis omitted, it defaults to point.name, if non-nil, should be the name by which this abbrev was found (a string); it is used to figure out whether to adjust the capitalization of the expansion. The function returnsabbrevif the abbrev was successfully inserted, otherwise it returnsnil.
This command marks the current location of point as the beginning of an abbrev. The next call to
expand-abbrevwill use the text from here to point (where it is then) as the abbrev to expand, rather than using the previous word as usual.First, this command expands any abbrev before point, unless arg is non-
nil. (Interactively, arg is the prefix argument.) Then it inserts a hyphen before point, to indicate the start of the next abbrev to be expanded. The actual expansion removes the hyphen.
When this is set non-
nil, an abbrev entered entirely in upper case is expanded using all upper case. Otherwise, an abbrev entered entirely in upper case is expanded by capitalizing each word of the expansion.
The value of this variable is a buffer position (an integer or a marker) for
expand-abbrevto use as the start of the next abbrev to be expanded. The value can also benil, which means to use the word before point instead.abbrev-start-locationis set tonileach timeexpand-abbrevis called. This variable is also set byabbrev-prefix-mark.
The value of this variable is the buffer for which
abbrev-start-locationhas been set. Trying to expand an abbrev in any other buffer clearsabbrev-start-location. This variable is set byabbrev-prefix-mark.
This is the
abbrev-symbolof the most recent abbrev expanded. This information is left byexpand-abbrevfor the sake of theunexpand-abbrevcommand (see Expanding Abbrevs).
This is the location of the most recent abbrev expanded. This contains information left by
expand-abbrevfor the sake of theunexpand-abbrevcommand.
This is the exact expansion text of the most recent abbrev expanded, after case conversion (if any). Its value is
nilif the abbrev has already been unexpanded. This contains information left byexpand-abbrevfor the sake of theunexpand-abbrevcommand.
The value of this variable is a function that
expand-abbrevwill call with no arguments to do the expansion. The function can do anything it wants before and after performing the expansion. It should return the abbrev symbol if expansion took place.
The following sample code shows a simple use of
abbrev-expand-function. It assumes that foo-mode is a
mode for editing certain files in which lines that start with `#'
are comments. You want to use Text mode abbrevs for those lines. The
regular local abbrev table, foo-mode-abbrev-table is
appropriate for all other lines. See Standard Abbrev Tables, for the
definitions of local-abbrev-table and text-mode-abbrev-table.
See Advising Functions, for details of add-function.
(defun foo-mode-abbrev-expand-function (expand)
(if (not (save-excursion (forward-line 0) (eq (char-after) ?#)))
;; Performs normal expansion.
(funcall expand)
;; We're inside a comment: use the text-mode abbrevs.
(let ((local-abbrev-table text-mode-abbrev-table))
(funcall expand))))
(add-hook 'foo-mode-hook
#'(lambda ()
(add-function :around (local 'abbrev-expand-function)
#'foo-mode-abbrev-expand-function)))
Here we list the variables that hold the abbrev tables for the preloaded major modes of Emacs.
This is the abbrev table for mode-independent abbrevs. The abbrevs defined in it apply to all buffers. Each buffer may also have a local abbrev table, whose abbrev definitions take precedence over those in the global table.
The value of this buffer-local variable is the (mode-specific) abbreviation table of the current buffer. It can also be a list of such tables.
The value of this variable is a list of elements of the form
(mode.abbrev-table)where mode is the name of a variable: if the variable is bound to a non-nilvalue, then the abbrev-table is active, otherwise it is ignored. abbrev-table can also be a list of abbrev tables.
This is the local abbrev table used in Fundamental mode; in other words, it is the local abbrev table in all buffers in Fundamental mode.
This is the local abbrev table used in Lisp mode. It is the parent of the local abbrev table used in Emacs Lisp mode. See Abbrev Table Properties.
Abbrevs have properties, some of which influence the way they work.
You can provide them as arguments to define-abbrev, and
manipulate them with the following functions:
Return the property prop of abbrev, or
nilif the abbrev has no such property.
The following properties have special meanings:
:countdefine-abbrev.
:systemnil, this property marks the abbrev as a system abbrev.
Such abbrevs are not saved (see Abbrev Files).
:enable-functionnil, this property should be a function of no
arguments which returns nil if the abbrev should not be used
and t otherwise.
:case-fixednil, this property indicates that the case of the
abbrev's name is significant and should only match a text with the
same pattern of capitalization. It also disables the code that
modifies the capitalization of the expansion.
Like abbrevs, abbrev tables have properties, some of which influence
the way they work. You can provide them as arguments to
define-abbrev-table, and manipulate them with the functions:
Set the property prop of abbrev table table to value val.
Return the property prop of abbrev table table, or
nilif the abbrev has no such property.
The following properties have special meaning:
:enable-function:enable-function abbrev property except that
it applies to all abbrevs in the table. It is used before even trying
to find the abbrev before point, so it can dynamically modify the
abbrev table.
:case-fixed:case-fixed abbrev property except that it
applies to all abbrevs in the table.
:regexpnil, this property is a regular expression that
indicates how to extract the name of the abbrev before point, before
looking it up in the table. When the regular expression matches
before point, the abbrev name is expected to be in submatch 1.
If this property is nil, the default is to use
backward-word and forward-word to find the name. This
property allows the use of abbrevs whose name contains characters of
non-word syntax.
:parents:abbrev-table-modiffIn the terminology of operating systems, a process is a space in which a program can execute. Emacs runs in a process. Emacs Lisp programs can invoke other programs in processes of their own. These are called subprocesses or child processes of the Emacs process, which is their parent process.
A subprocess of Emacs may be synchronous or asynchronous, depending on how it is created. When you create a synchronous subprocess, the Lisp program waits for the subprocess to terminate before continuing execution. When you create an asynchronous subprocess, it can run in parallel with the Lisp program. This kind of subprocess is represented within Emacs by a Lisp object which is also called a “process”. Lisp programs can use this object to communicate with the subprocess or to control it. For example, you can send signals, obtain status information, receive output from the process, or send input to it.
This function returns
tif object represents an Emacs subprocess,nilotherwise.
In addition to subprocesses of the current Emacs session, you can also access other processes running on your machine. See System Processes.
There are three primitives that create a new subprocess in which to run
a program. One of them, start-process, creates an asynchronous
process and returns a process object (see Asynchronous Processes).
The other two, call-process and call-process-region,
create a synchronous process and do not return a process object
(see Synchronous Processes). There are various higher-level
functions that make use of these primitives to run particular types of
process.
Synchronous and asynchronous processes are explained in the following sections. Since the three functions are all called in a similar fashion, their common arguments are described here.
In all cases, the function's program argument specifies the
program to be run. An error is signaled if the file is not found or
cannot be executed. If the file name is relative, the variable
exec-path contains a list of directories to search. Emacs
initializes exec-path when it starts up, based on the value of
the environment variable PATH. The standard file name
constructs, `~', `.', and `..', are interpreted as
usual in exec-path, but environment variable substitutions
(`$HOME', etc.) are not recognized; use
substitute-in-file-name to perform them (see File Name Expansion). nil in this list refers to
default-directory.
Executing a program can also try adding suffixes to the specified name:
This variable is a list of suffixes (strings) to try adding to the specified program file name. The list should include
""if you want the name to be tried exactly as specified. The default value is system-dependent.
Please note: The argument program contains only the name of the program; it may not contain any command-line arguments. You must use a separate argument, args, to provide those, as described below.
Each of the subprocess-creating functions has a buffer-or-name
argument that specifies where the standard output from the program will
go. It should be a buffer or a buffer name; if it is a buffer name,
that will create the buffer if it does not already exist. It can also
be nil, which says to discard the output, unless a custom filter function
handles it. (See Filter Functions, and Read and Print.)
Normally, you should avoid having multiple processes send output to the
same buffer because their output would be intermixed randomly.
For synchronous processes, you can send the output to a file instead
of a buffer.
All three of the subprocess-creating functions have a &rest
argument, args. The args must all be strings, and they are
supplied to program as separate command line arguments. Wildcard
characters and other shell constructs have no special meanings in these
strings, since the strings are passed directly to the specified program.
The subprocess inherits its environment from Emacs, but you can
specify overrides for it with process-environment. See System Environment. The subprocess gets its current directory from the
value of default-directory.
The value of this variable is a string, the name of a directory that contains programs that come with GNU Emacs and are intended for Emacs to invoke. The program
movemailis an example of such a program; Rmail uses it to fetch new mail from an inbox.
The value of this variable is a list of directories to search for programs to run in subprocesses. Each element is either the name of a directory (i.e., a string), or
nil, which stands for the default directory (which is the value ofdefault-directory). The value ofexec-pathis used bycall-processandstart-processwhen the program argument is not an absolute file name.Generally, you should not modify
exec-pathdirectly. Instead, ensure that your PATH environment variable is set appropriately before starting Emacs. Trying to modifyexec-pathindependently of PATH can lead to confusing results.
Lisp programs sometimes need to run a shell and give it a command
that contains file names that were specified by the user. These
programs ought to be able to support any valid file name. But the shell
gives special treatment to certain characters, and if these characters
occur in the file name, they will confuse the shell. To handle these
characters, use the function shell-quote-argument:
This function returns a string that represents, in shell syntax, an argument whose actual contents are argument. It should work reliably to concatenate the return value into a shell command and then pass it to a shell for execution.
Precisely what this function does depends on your operating system. The function is designed to work with the syntax of your system's standard shell; if you use an unusual shell, you will need to redefine this function. See Security Considerations.
;; This example shows the behavior on GNU and Unix systems. (shell-quote-argument "foo > bar") => "foo\\ \\>\\ bar" ;; This example shows the behavior on MS-DOS and MS-Windows. (shell-quote-argument "foo > bar") => "\"foo > bar\""Here's an example of using
shell-quote-argumentto construct a shell command:(concat "diff -u " (shell-quote-argument oldfile) " " (shell-quote-argument newfile))
The following two functions are useful for combining a list of
individual command-line argument strings into a single string, and
taking a string apart into a list of individual command-line
arguments. These functions are mainly intended for
converting user input in the minibuffer, a Lisp string, into a list of
string arguments to be passed to call-process or
start-process, or for converting such lists of arguments into
a single Lisp string to be presented in the minibuffer or echo area.
This function splits string into substrings at matches for the regular expression separators, like
split-stringdoes (see Creating Strings); in addition, it removes quoting from the substrings. It then makes a list of the substrings and returns it.If separators is omitted or
nil, it defaults to"\\s-+", which is a regular expression that matches one or more characters with whitespace syntax (see Syntax Class Table).This function supports two types of quoting: enclosing a whole string in double quotes
"...", and quoting individual characters with a backslash escape `\'. The latter is also used in Lisp strings, so this function can handle those as well.
This function concatenates list-of-strings into a single string, quoting each string as necessary. It also sticks the separator string between each pair of strings; if separator is omitted or
nil, it defaults to" ". The return value is the resulting string.The strings in list-of-strings that need quoting are those that include separator as their substring. Quoting a string encloses it in double quotes
"...". In the simplest case, if you are consing a command from the individual command-line arguments, every argument that includes embedded blanks will be quoted.
After a synchronous process is created, Emacs waits for the
process to terminate before continuing. Starting Dired on GNU or
Unix18 is an example of this: it
runs ls in a synchronous process, then modifies the output
slightly. Because the process is synchronous, the entire directory
listing arrives in the buffer before Emacs tries to do anything with it.
While Emacs waits for the synchronous subprocess to terminate, the
user can quit by typing C-g. The first C-g tries to kill
the subprocess with a SIGINT signal; but it waits until the
subprocess actually terminates before quitting. If during that time the
user types another C-g, that kills the subprocess instantly with
SIGKILL and quits immediately (except on MS-DOS, where killing
other processes doesn't work). See Quitting.
The synchronous subprocess functions return an indication of how the process terminated.
The output from a synchronous subprocess is generally decoded using a
coding system, much like text read from a file. The input sent to a
subprocess by call-process-region is encoded using a coding
system, much like text written into a file. See Coding Systems.
This function calls program and waits for it to finish.
The current working directory of the subprocess is
default-directory.The standard input for the new process comes from file infile if infile is not
nil, and from the null device otherwise. The argument destination says where to put the process output. Here are the possibilities:
- a buffer
- Insert the output in that buffer, before point. This includes both the standard output stream and the standard error stream of the process.
- a buffer name (a string)
- Insert the output in a buffer with that name, before point.
t- Insert the output in the current buffer, before point.
nil- Discard the output.
- 0
- Discard the output, and return
nilimmediately without waiting for the subprocess to finish.In this case, the process is not truly synchronous, since it can run in parallel with Emacs; but you can think of it as synchronous in that Emacs is essentially finished with the subprocess as soon as this function returns.
MS-DOS doesn't support asynchronous subprocesses, so this option doesn't work there.
(:filefile-name)- Send the output to the file name specified, overwriting it if it already exists.
(real-destination error-destination)- Keep the standard output stream separate from the standard error stream; deal with the ordinary output as specified by real-destination, and dispose of the error output according to error-destination. If error-destination is
nil, that means to discard the error output,tmeans mix it with the ordinary output, and a string specifies a file name to redirect error output into.You can't directly specify a buffer to put the error output in; that is too difficult to implement. But you can achieve this result by sending the error output to a temporary file and then inserting the file into a buffer.
If display is non-
nil, thencall-processredisplays the buffer as output is inserted. (However, if the coding system chosen for decoding output isundecided, meaning deduce the encoding from the actual data, then redisplay sometimes cannot continue once non-ASCII characters are encountered. There are fundamental reasons why it is hard to fix this; see Output from Processes.)Otherwise the function
call-processdoes no redisplay, and the results become visible on the screen only when Emacs redisplays that buffer in the normal course of events.The remaining arguments, args, are strings that specify command line arguments for the program.
The value returned by
call-process(unless you told it not to wait) indicates the reason for process termination. A number gives the exit status of the subprocess; 0 means success, and any other value means failure. If the process terminated with a signal,call-processreturns a string describing the signal.In the examples below, the buffer `foo' is current.
(call-process "pwd" nil t) => 0 ---------- Buffer: foo ---------- /home/lewis/manual ---------- Buffer: foo ---------- (call-process "grep" nil "bar" nil "lewis" "/etc/passwd") => 0 ---------- Buffer: bar ---------- lewis:x:1001:1001:Bil Lewis,,,,:/home/lewis:/bin/bash ---------- Buffer: bar ----------Here is an example of the use of
call-process, as used to be found in the definition of theinsert-directoryfunction:(call-process insert-directory-program nil t nil switches (if full-directory-p (concat (file-name-as-directory file) ".") file))
This function processes files synchronously in a separate process. It is similar to
call-process, but may invoke a file handler based on the value of the variabledefault-directory, which specifies the current working directory of the subprocess.The arguments are handled in almost the same way as for
call-process, with the following differences:Some file handlers may not support all combinations and forms of the arguments infile, buffer, and display. For example, some file handlers might behave as if display were
nil, regardless of the value actually passed. As another example, some file handlers might not support separating standard output and error output by way of the buffer argument.If a file handler is invoked, it determines the program to run based on the first argument program. For instance, suppose that a handler for remote files is invoked. Then the path that is used for searching for the program might be different from
exec-path.The second argument infile may invoke a file handler. The file handler could be different from the handler chosen for the
process-filefunction itself. (For example,default-directorycould be on one remote host, and infile on a different remote host. Ordefault-directorycould be non-special, whereas infile is on a remote host.)If buffer is a list of the form
(real-destination error-destination), and error-destination names a file, then the same remarks as for infile apply.The remaining arguments (args) will be passed to the process verbatim. Emacs is not involved in processing file names that are present in args. To avoid confusion, it may be best to avoid absolute file names in args, but rather to specify all file names as relative to
default-directory. The functionfile-relative-nameis useful for constructing such relative file names.
This variable indicates whether a call of
process-filechanges remote files.By default, this variable is always set to
t, meaning that a call ofprocess-filecould potentially change any file on a remote host. When set tonil, a file handler could optimize its behavior with respect to remote file attribute caching.You should only ever change this variable with a let-binding; never with
setq.
This function sends the text from start to end as standard input to a process running program. It deletes the text sent if delete is non-
nil; this is useful when destination ist, to insert the output in the current buffer in place of the input.The arguments destination and display control what to do with the output from the subprocess, and whether to update the display as it comes in. For details, see the description of
call-process, above. If destination is the integer 0,call-process-regiondiscards the output and returnsnilimmediately, without waiting for the subprocess to finish (this only works if asynchronous subprocesses are supported; i.e., not on MS-DOS).The remaining arguments, args, are strings that specify command line arguments for the program.
The return value of
call-process-regionis just like that ofcall-process:nilif you told it to return without waiting; otherwise, a number or string which indicates how the subprocess terminated.In the following example, we use
call-process-regionto run thecatutility, with standard input being the first five characters in buffer `foo' (the word `input').catcopies its standard input into its standard output. Since the argument destination ist, this output is inserted in the current buffer.---------- Buffer: foo ---------- input-!- ---------- Buffer: foo ---------- (call-process-region 1 6 "cat" nil t) => 0 ---------- Buffer: foo ---------- inputinput-!- ---------- Buffer: foo ----------For example, the
shell-command-on-regioncommand usescall-process-regionin a manner similar to this:(call-process-region start end shell-file-name ; name of program nil ; do not delete region buffer ; send output tobuffernil ; no redisplay during output "-c" command) ; arguments for the shell
This function executes the shell command command synchronously. The arguments are handled as in
call-process. An old calling convention allowed to pass any number of additional arguments after display, which were concatenated to command; this is still supported, but strongly discouraged.
This function is like
call-process-shell-command, but usesprocess-fileinternally. Depending ondefault-directory, command can be executed also on remote hosts. An old calling convention allowed to pass any number of additional arguments after display, which were concatenated to command; this is still supported, but strongly discouraged.
This function executes command (a string) as a shell command, then returns the command's output as a string.
This function runs program, waits for it to finish, and returns its output as a list of strings. Each string in the list holds a single line of text output by the program; the end-of-line characters are stripped from each line. The arguments beyond program, args, are strings that specify command-line arguments with which to run the program.
If program exits with a non-zero exit status, this function signals an error.
This function works by calling
call-process, so program output is decoded in the same way as forcall-process.
In this section, we describe how to create an asynchronous process. After an asynchronous process is created, it runs in parallel with Emacs, and Emacs can communicate with it using the functions described in the following sections (see Input to Processes, and see Output from Processes). Note that process communication is only partially asynchronous: Emacs sends data to the process only when certain functions are called, and Emacs accepts data from the process only while waiting for input or for a time delay.
An asynchronous process is controlled either via a pty
(pseudo-terminal) or a pipe. The choice of pty or pipe is made
when creating the process, based on the value of the variable
process-connection-type (see below). Ptys are usually
preferable for processes visible to the user, as in Shell mode,
because they allow for job control (C-c, C-z, etc.)
between the process and its children, whereas pipes do not. For
subprocesses used for internal purposes by programs, it is often
better to use a pipe, because they are more efficient, and because
they are immune to stray character injections that ptys introduce for
large (around 500 byte) messages. Also, the total number of ptys is
limited on many systems and it is good not to waste them.
This function creates a new asynchronous subprocess and starts the program program running in it. It returns a process object that stands for the new subprocess in Lisp. The argument name specifies the name for the process object; if a process with this name already exists, then name is modified (by appending `<1>', etc.) to be unique. The buffer buffer-or-name is the buffer to associate with the process.
If program is
nil, Emacs opens a new pseudoterminal (pty) and associates its input and output with buffer-or-name, without creating a subprocess. In that case, the remaining arguments args are ignored.The remaining arguments, args, are strings that specify command line arguments for the subprocess.
In the example below, the first process is started and runs (rather, sleeps) for 100 seconds (the output buffer `foo' is created immediately). Meanwhile, the second process is started, and given the name `my-process<1>' for the sake of uniqueness. It inserts the directory listing at the end of the buffer `foo', before the first process finishes. Then it finishes, and a message to that effect is inserted in the buffer. Much later, the first process finishes, and another message is inserted in the buffer for it.
(start-process "my-process" "foo" "sleep" "100") => #<process my-process> (start-process "my-process" "foo" "ls" "-l" "/bin") => #<process my-process<1>> ---------- Buffer: foo ---------- total 8336 -rwxr-xr-x 1 root root 971384 Mar 30 10:14 bash -rwxr-xr-x 1 root root 146920 Jul 5 2011 bsd-csh ... -rwxr-xr-x 1 root root 696880 Feb 28 15:55 zsh4 Process my-process<1> finished Process my-process finished ---------- Buffer: foo ----------
Like
start-process, this function starts a new asynchronous subprocess running program in it, and returns its process object.The difference from
start-processis that this function may invoked a file handler based on the value ofdefault-directory. This handler ought to run program, perhaps on the local host, perhaps on a remote host that corresponds todefault-directory. In the latter case, the local part ofdefault-directorybecomes the working directory of the process.This function does not try to invoke file name handlers for program or for the program-args.
Depending on the implementation of the file handler, it might not be possible to apply
process-filterorprocess-sentinelto the resulting process object. See Filter Functions, and Sentinels.Some file handlers may not support
start-file-process(for example the functionange-ftp-hook-function). In such cases, this function does nothing and returnsnil.
This function is like
start-process, except that it uses a shell to execute the specified command. The argument command is a shell command name. The variableshell-file-namespecifies which shell to use.The point of running a program through the shell, rather than directly with
start-process, is so that you can employ shell features such as wildcards in the arguments. It follows that if you include any arbitrary user-specified arguments in the command, you should quote them withshell-quote-argumentfirst, so that any special shell characters do not have their special shell meanings. See Shell Arguments. Of course, when executing commands based on user input you should also consider the security implications.
This function is like
start-process-shell-command, but usesstart-file-processinternally. Because of this, command can also be executed on remote hosts, depending ondefault-directory.
This variable controls the type of device used to communicate with asynchronous subprocesses. If it is non-
nil, then ptys are used, when available. Otherwise, pipes are used.The value of
process-connection-typetakes effect whenstart-processis called. So you can specify how to communicate with one subprocess by binding the variable around the call tostart-process.(let ((process-connection-type nil)) ; use a pipe (start-process ...))To determine whether a given subprocess actually got a pipe or a pty, use the function
process-tty-name(see Process Information).
This function is like
start-process, but takes keyword arguments.The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value
nil. Here are the meaningful keywords:
- :name name
- Use the string name as the process name. It is modified if necessary to make it unique.
- :buffer buffer
- Use buffer as the process buffer.
- :command command
- Use command as the command line of the process. command is a list starting with the program's executable file name, followed by strings to give to program as arguments.
- :coding coding
- If coding is a symbol, it specifies the coding system to be used for both reading and writing of data from and to the connection. If coding is a cons cell
(decoding.encoding), then decoding will be used for reading and encoding for writing.If coding is
nil, the default rules for finding the coding system will apply. See Default Coding Systems.- :connection-type TYPE
- Initialize the type of device used to communicate with the subprocess. Possible values are
ptyto use a pty,pipeto use a pipe, ornilto use the default derived from the value of theprocess-connection-typevariable.
- :noquery query-flag
- Initialize the process query flag to query-flag. See Query Before Exit.
- :stop stopped
- If stopped is non-
nil, start the process in the stopped state.
- :filter filter
- Initialize the process filter to filter. If not specified, a default filter will be provided. See Filter Functions.
- :sentinel sentinel
- Initialize the process sentinel to sentinel. If not specified, a default sentinel will be used. See Sentinels.
- :stderr stderr
- Associate stderr with the standard error of the process. stderr is either a buffer or a pipe process created with
make-pipe-process.The original argument list, modified with the actual connection information, is available via the
process-contactfunction.
This function creates a bidirectional pipe which can be attached to a child process (currently only useful with the
:stderrkeyword ofmake-process).The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value
nil, except for:coding. Here are the meaningful keywords:
- :name name
- Use the string name as the process name. It is modified if necessary to make it unique.
- :buffer buffer
- Use buffer as the process buffer.
- :coding coding
- If coding is a symbol, it specifies the coding system to be used for both reading and writing of data from and to the connection. If coding is a cons cell
(decoding.encoding), then decoding will be used for reading and encoding for writing.If coding is
nil, the default rules for finding the coding system will apply. See Default Coding Systems.- :noquery query-flag
- Initialize the process query flag to query-flag. See Query Before Exit.
- :stop stopped
- If stopped is non-
nil, start the process in the stopped state.
- :filter filter
- Initialize the process filter to filter. If not specified, a default filter will be provided. See Filter Functions.
- :sentinel sentinel
- Initialize the process sentinel to sentinel. If not specified, a default sentinel will be used. See Sentinels.
The original argument list, modified with the actual connection information, is available via the
process-contactfunction.
Deleting a process disconnects Emacs immediately from the subprocess. Processes are deleted automatically after they terminate, but not necessarily right away. You can delete a process explicitly at any time. If you explicitly delete a terminated process before it is deleted automatically, no harm results. Deleting a running process sends a signal to terminate it (and its child processes, if any), and calls the process sentinel. See Sentinels.
When a process is deleted, the process object itself continues to exist as long as other Lisp objects point to it. All the Lisp primitives that work on process objects accept deleted processes, but those that do I/O or send signals will report an error. The process mark continues to point to the same place as before, usually into a buffer where output from the process was being inserted.
This variable controls automatic deletion of processes that have terminated (due to calling
exitor to a signal). If it isnil, then they continue to exist until the user runslist-processes. Otherwise, they are deleted immediately after they exit.
This function deletes a process, killing it with a
SIGKILLsignal. The argument may be a process, the name of a process, a buffer, or the name of a buffer. (A buffer or buffer-name stands for the process thatget-buffer-processreturns.) Callingdelete-processon a running process terminates it, updates the process status, and runs the sentinel immediately. If the process has already terminated, callingdelete-processhas no effect on its status, or on the running of its sentinel (which will happen sooner or later).(delete-process "*shell*") => nil
Several functions return information about processes.
This command displays a listing of all living processes. In addition, it finally deletes any process whose status was `Exited' or `Signaled'. It returns
nil.The processes are shown in a buffer named *Process List* (unless you specify otherwise using the optional argument buffer), whose major mode is Process Menu mode.
If query-only is non-
nil, it only lists processes whose query flag is non-nil. See Query Before Exit.
This function returns a list of all processes that have not been deleted.
(process-list) => (#<process display-time> #<process shell>)
This function returns the process named name (a string), or
nilif there is none.(get-process "shell") => #<process shell>
This function returns the command that was executed to start process. This is a list of strings, the first string being the program executed and the rest of the strings being the arguments that were given to the program.
(process-command (get-process "shell")) => ("bash" "-i")
This function returns information about how a network or serial process was set up. When key is
nil, it returns(hostname service)for a network process, and(port speed)for a serial process. For an ordinary child process, this function always returnst.If key is
t, the value is the complete status information for the connection, server, or serial port; that is, the list of keywords and values specified inmake-network-processormake-serial-process, except that some of the values represent the current status instead of what you specified.For a network process, the values include (see
make-network-processfor a complete list):
:buffer- The associated value is the process buffer.
:filter- The associated value is the process filter function. See Filter Functions.
:sentinel- The associated value is the process sentinel function. See Sentinels.
:remote- In a connection, the address in internal format of the remote peer.
:local- The local address, in internal format.
:service- In a server, if you specified
tfor service, this value is the actual port number.
:localand:remoteare included even if they were not specified explicitly inmake-network-process.For a serial process, see
make-serial-processandserial-process-configurefor a list of keys.If key is a keyword, the function returns the value corresponding to that keyword.
This function returns the PID of process. This is an integer that distinguishes the process process from all other processes running on the same computer at the current time. The PID of a process is chosen by the operating system kernel when the process is started and remains constant as long as the process exists.
This function returns the status of process-name as a symbol. The argument process-name must be a process, a buffer, or a process name (a string).
The possible values for an actual subprocess are:
run- for a process that is running.
stop- for a process that is stopped but continuable.
exit- for a process that has exited.
signal- for a process that has received a fatal signal.
open- for a network connection that is open.
closed- for a network connection that is closed. Once a connection is closed, you cannot reopen it, though you might be able to open a new connection to the same place.
connect- for a non-blocking connection that is waiting to complete.
failed- for a non-blocking connection that has failed to complete.
listen- for a network server that is listening.
nil- if process-name is not the name of an existing process.
(process-status (get-buffer "*shell*")) => runFor a network connection,
process-statusreturns one of the symbolsopenorclosed. The latter means that the other side closed the connection, or Emacs diddelete-process.
This function returns non-
nilif process is alive. A process is considered alive if its status isrun,open,listen,connectorstop.
This function returns the symbol
networkfor a network connection or server,serialfor a serial port connection, orrealfor a real subprocess.
This function returns the exit status of process or the signal number that killed it. (Use the result of
process-statusto determine which of those it is.) If process has not yet terminated, the value is 0.
This function returns the terminal name that process is using for its communication with Emacs—or
nilif it is using pipes instead of a terminal (seeprocess-connection-typein Asynchronous Processes). If process represents a program running on a remote host, the terminal name used by that program on the remote host is provided as process propertyremote-tty.
This function returns a cons cell
(decode.encode), describing the coding systems in use for decoding output from, and encoding input to, process (see Coding Systems).
This function specifies the coding systems to use for subsequent output from and input to process. It will use decoding-system to decode subprocess output, and encoding-system to encode subprocess input.
Every process also has a property list that you can use to store miscellaneous values associated with the process.
This function returns the value of the propname property of process.
This function sets the value of the propname property of process to value.
This function sets the process plist of process to plist.
Asynchronous subprocesses receive input when it is sent to them by Emacs, which is done with the functions in this section. You must specify the process to send input to, and the input data to send. The data appears on the standard input of the subprocess.
Some operating systems have limited space for buffered input in a pty. On these systems, Emacs sends an EOF periodically amidst the other characters, to force them through. For most programs, these EOFs do no harm.
Subprocess input is normally encoded using a coding system before the
subprocess receives it, much like text written into a file. You can use
set-process-coding-system to specify which coding system to use
(see Process Information). Otherwise, the coding system comes from
coding-system-for-write, if that is non-nil; or else from
the defaulting mechanism (see Default Coding Systems).
Sometimes the system is unable to accept input for that process, because the input buffer is full. When this happens, the send functions wait a short while, accepting output from subprocesses, and then try again. This gives the subprocess a chance to read more of its pending input and make space in the buffer. It also allows filters, sentinels and timers to run—so take account of that in writing your code.
In these functions, the process argument can be a process or
the name of a process, or a buffer or buffer name (which stands
for a process via get-buffer-process). nil means
the current buffer's process.
This function sends process the contents of string as standard input. It returns
nil. For example, to make a Shell buffer list files:(process-send-string "shell<1>" "ls\n") => nil
This function sends the text in the region defined by start and end as standard input to process.
An error is signaled unless both start and end are integers or markers that indicate positions in the current buffer. (It is unimportant which number is larger.)
This function makes process see an end-of-file in its input. The EOF comes after any text already sent to it. The function returns process.
(process-send-eof "shell") => "shell"
This function will tell you whether a process has given control of its terminal to its own child process. If this is true, the function returns the numeric ID of the foreground process group of process; it returns
nilif Emacs can be certain that this is not so. The value istif Emacs cannot tell whether this is true.
Sending a signal to a subprocess is a way of interrupting its
activities. There are several different signals, each with its own
meaning. The set of signals and their names is defined by the operating
system. For example, the signal SIGINT means that the user has
typed C-c, or that some analogous thing has happened.
Each signal has a standard effect on the subprocess. Most signals kill the subprocess, but some stop (or resume) execution instead. Most signals can optionally be handled by programs; if the program handles the signal, then we can say nothing in general about its effects.
You can send signals explicitly by calling the functions in this
section. Emacs also sends signals automatically at certain times:
killing a buffer sends a SIGHUP signal to all its associated
processes; killing Emacs sends a SIGHUP signal to all remaining
processes. (SIGHUP is a signal that usually indicates that the
user “hung up the phone”, i.e., disconnected.)
Each of the signal-sending functions takes two optional arguments: process and current-group.
The argument process must be either a process, a process
name, a buffer, a buffer name, or nil. A buffer or buffer name
stands for a process through get-buffer-process. nil
stands for the process associated with the current buffer. An error
is signaled if process does not identify a process.
The argument current-group is a flag that makes a difference
when you are running a job-control shell as an Emacs subprocess. If it
is non-nil, then the signal is sent to the current process-group
of the terminal that Emacs uses to communicate with the subprocess. If
the process is a job-control shell, this means the shell's current
subjob. If it is nil, the signal is sent to the process group of
the immediate subprocess of Emacs. If the subprocess is a job-control
shell, this is the shell itself.
The flag current-group has no effect when a pipe is used to
communicate with the subprocess, because the operating system does not
support the distinction in the case of pipes. For the same reason,
job-control shells won't work when a pipe is used. See
process-connection-type in Asynchronous Processes.
This function interrupts the process process by sending the signal
SIGINT. Outside of Emacs, typing the interrupt character (normally C-c on some systems, and <DEL> on others) sends this signal. When the argument current-group is non-nil, you can think of this function as typing C-c on the terminal by which Emacs talks to the subprocess.
This function kills the process process by sending the signal
SIGKILL. This signal kills the subprocess immediately, and cannot be handled by the subprocess.
This function sends the signal
SIGQUITto the process process. This signal is the one sent by the quit character (usually C-\) when you are not inside Emacs.
This function stops the process process by sending the signal
SIGTSTP. Usecontinue-processto resume its execution.Outside of Emacs, on systems with job control, the stop character (usually C-z) normally sends this signal. When current-group is non-
nil, you can think of this function as typing C-z on the terminal Emacs uses to communicate with the subprocess.
This function resumes execution of the process process by sending it the signal
SIGCONT. This presumes that process was stopped previously.
This function sends a signal to process process. The argument signal specifies which signal to send; it should be an integer, or a symbol whose name is a signal.
The process argument can be a system process ID (an integer); that allows you to send signals to processes that are not children of Emacs. See System Processes.
The output that a subprocess writes to its standard output stream is passed to a function called the filter function. The default filter function simply inserts the output into a buffer, which is called the associated buffer of the process (see Process Buffers). If the process has no buffer then the default filter discards the output.
When a subprocess terminates, Emacs reads any pending output, then stops reading output from that subprocess. Therefore, if the subprocess has children that are still live and still producing output, Emacs won't receive that output.
Output from a subprocess can arrive only while Emacs is waiting: when
reading terminal input (see the function waiting-for-user-input-p),
in sit-for and sleep-for (see Waiting), and in
accept-process-output (see Accepting Output). This
minimizes the problem of timing errors that usually plague parallel
programming. For example, you can safely create a process and only
then specify its buffer or filter function; no output can arrive
before you finish, if the code in between does not call any primitive
that waits.
On some systems, when Emacs reads the output from a subprocess, the output data is read in very small blocks, potentially resulting in very poor performance. This behavior can be remedied to some extent by setting the variable
process-adaptive-read-bufferingto a non-nilvalue (the default), as it will automatically delay reading from such processes, thus allowing them to produce more output before Emacs tries to read it.
It is impossible to separate the standard output and standard error streams of the subprocess, because Emacs normally spawns the subprocess inside a pseudo-TTY, and a pseudo-TTY has only one output channel. If you want to keep the output to those streams separate, you should redirect one of them to a file—for example, by using an appropriate shell command.
A process can (and usually does) have an associated buffer, which is an ordinary Emacs buffer that is used for two purposes: storing the output from the process, and deciding when to kill the process. You can also use the buffer to identify a process to operate on, since in normal practice only one process is associated with any given buffer. Many applications of processes also use the buffer for editing input to be sent to the process, but this is not built into Emacs Lisp.
By default, process output is inserted in the associated buffer.
(You can change this by defining a custom filter function,
see Filter Functions.) The position to insert the output is
determined by the process-mark, which is then updated to point
to the end of the text just inserted. Usually, but not always, the
process-mark is at the end of the buffer.
Killing the associated buffer of a process also kills the process.
Emacs asks for confirmation first, if the process's
process-query-on-exit-flag is non-nil (see Query Before Exit). This confirmation is done by the function
process-kill-buffer-query-function, which is run from
kill-buffer-query-functions (see Killing Buffers).
This function returns the associated buffer of the process process.
(process-buffer (get-process "shell")) => #<buffer *shell*>
This function returns the process marker for process, which is the marker that says where to insert output from the process.
If process does not have a buffer,
process-markreturns a marker that points nowhere.The default filter function uses this marker to decide where to insert process output, and updates it to point after the inserted text. That is why successive batches of output are inserted consecutively.
Custom filter functions normally should use this marker in the same fashion. For an example of a filter function that uses
process-mark, see Process Filter Example.When the user is expected to enter input in the process buffer for transmission to the process, the process marker separates the new input from previous output.
This function sets the buffer associated with process to buffer. If buffer is
nil, the process becomes associated with no buffer.
This function returns a nondeleted process associated with the buffer specified by buffer-or-name. If there are several processes associated with it, this function chooses one (currently, the one most recently created, but don't count on that). Deletion of a process (see
delete-process) makes it ineligible for this function to return.It is usually a bad idea to have more than one process associated with the same buffer.
(get-buffer-process "*shell*") => #<process shell>Killing the process's buffer deletes the process, which kills the subprocess with a
SIGHUPsignal (see Signals to Processes).
If the process's buffer is displayed in a window, your Lisp program may wish telling the process the dimensions of that window, so that the process could adapt its output to those dimensions, much as it adapts to the screen dimensions. The following functions allow to communicate this kind of information to processes; however, not all systems support the underlying functionality, so it is best to provide fallbacks, e.g., via command-line arguments or environment variables.
Tell process that its logical window size has dimensions width by height, in character units. If this function succeeds in communicating this information to the process, it returns
t; otherwise it returnsnil.
When windows that display buffers associated with process change their
dimensions, the affected processes should be told about these changes.
By default, when the window configuration changes, Emacs will
automatically call set-process-window-size on behalf of every
process whose buffer is displayed in a window, passing it the smallest
dimensions of all the windows displaying the process's buffer. This
works via window-configuration-change-hook (see Window Hooks), which is told to invoke the function that is the value of
the variable window-adjust-process-window-size-function for
each process whose buffer is displayed in at least one window. You
can customize this behavior by setting the value of that variable.
The value of this variable should be a function of two arguments: a process and the list of windows displaying the process's buffer. When the function is called, the process's buffer is the current buffer. The function should return a cons cell
(width.height)that describes the dimensions of the logical process window to be passed via a call toset-process-window-size. The function can also returnnil, in which case Emacs will not callset-process-window-sizefor this process.Emacs supplies two predefined values for this variable:
window-adjust-process-window-size-smallest, which returns the smallest of all the dimensions of the windows that display a process's buffer; andwindow-adjust-process-window-size-largest, which returns the largest dimensions. For more complex strategies, write your own function.This variable can be buffer-local.
If the process has the adjust-window-size-function property
(see Process Information), its value overrides the global and
buffer-local values of
window-adjust-process-window-size-function.
A process filter function is a function that receives the standard output from the associated process. All output from that process is passed to the filter. The default filter simply outputs directly to the process buffer.
The filter function can only be called when Emacs is waiting for
something, because process output arrives only at such times. Emacs
waits when reading terminal input (see the function
waiting-for-user-input-p), in sit-for and
sleep-for (see Waiting), and in
accept-process-output (see Accepting Output).
A filter function must accept two arguments: the associated process and a string, which is output just received from it. The function is then free to do whatever it chooses with the output.
Quitting is normally inhibited within a filter function—otherwise,
the effect of typing C-g at command level or to quit a user
command would be unpredictable. If you want to permit quitting inside
a filter function, bind inhibit-quit to nil. In most
cases, the right way to do this is with the macro
with-local-quit. See Quitting.
If an error happens during execution of a filter function, it is
caught automatically, so that it doesn't stop the execution of whatever
program was running when the filter function was started. However, if
debug-on-error is non-nil, errors are not caught.
This makes it possible to use the Lisp debugger to debug the
filter function. See Debugger.
Many filter functions sometimes (or always) insert the output in the process's buffer, mimicking the actions of the default filter. Such filter functions need to make sure that they save the current buffer, select the correct buffer (if different) before inserting output, and then restore the original buffer. They should also check whether the buffer is still alive, update the process marker, and in some cases update the value of point. Here is how to do these things:
(defun ordinary-insertion-filter (proc string)
(when (buffer-live-p (process-buffer proc))
(with-current-buffer (process-buffer proc)
(let ((moving (= (point) (process-mark proc))))
(save-excursion
;; Insert the text, advancing the process marker.
(goto-char (process-mark proc))
(insert string)
(set-marker (process-mark proc) (point)))
(if moving (goto-char (process-mark proc)))))))
To make the filter force the process buffer to be visible whenever new
text arrives, you could insert a line like the following just before the
with-current-buffer construct:
(display-buffer (process-buffer proc))
To force point to the end of the new output, no matter where it was
previously, eliminate the variable moving and call
goto-char unconditionally.
Note that Emacs automatically saves and restores the match data while executing filter functions. See Match Data.
The output to the filter may come in chunks of any size. A program that produces the same output twice in a row may send it as one batch of 200 characters one time, and five batches of 40 characters the next. If the filter looks for certain text strings in the subprocess output, make sure to handle the case where one of these strings is split across two or more batches of output; one way to do this is to insert the received text into a temporary buffer, which can then be searched.
This function gives process the filter function filter. If filter is
nil, it gives the process the default filter, which inserts the process output into the process buffer.
In case the process's output needs to be passed to several filters, you can
use add-function to combine an existing filter with a new one.
See Advising Functions.
Here is an example of the use of a filter function:
(defun keep-output (process output)
(setq kept (cons output kept)))
=> keep-output
(setq kept nil)
=> nil
(set-process-filter (get-process "shell") 'keep-output)
=> keep-output
(process-send-string "shell" "ls ~/other\n")
=> nil
kept
=> ("lewis@slug:$ "
"FINAL-W87-SHORT.MSS backup.otl kolstad.mss~
address.txt backup.psf kolstad.psf
backup.bib~ david.mss resume-Dec-86.mss~
backup.err david.psf resume-Dec.psf
backup.mss dland syllabus.mss
"
"#backups.mss# backup.mss~ kolstad.mss
")
When Emacs writes process output directly into a multibyte buffer,
it decodes the output according to the process output coding system.
If the coding system is raw-text or no-conversion, Emacs
converts the unibyte output to multibyte using
string-to-multibyte, and inserts the resulting multibyte text.
You can use set-process-coding-system to specify which coding
system to use (see Process Information). Otherwise, the coding
system comes from coding-system-for-read, if that is
non-nil; or else from the defaulting mechanism (see Default Coding Systems). If the text output by a process contains null
bytes, Emacs by default uses no-conversion for it; see
inhibit-null-byte-detection, for how to
control this behavior.
Warning: Coding systems such as undecided, which
determine the coding system from the data, do not work entirely
reliably with asynchronous subprocess output. This is because Emacs
has to process asynchronous subprocess output in batches, as it
arrives. Emacs must try to detect the proper coding system from one
batch at a time, and this does not always work. Therefore, if at all
possible, specify a coding system that determines both the character
code conversion and the end of line conversion—that is, one like
latin-1-unix, rather than undecided or latin-1.
When Emacs calls a process filter function, it provides the process
output as a multibyte string or as a unibyte string according to the
process's filter coding system. Emacs
decodes the output according to the process output coding system,
which usually produces a multibyte string, except for coding systems
such as binary and raw-text.
Output from asynchronous subprocesses normally arrives only while Emacs is waiting for some sort of external event, such as elapsed time or terminal input. Occasionally it is useful in a Lisp program to explicitly permit output to arrive at a specific point, or even to wait until output arrives from a process.
This function allows Emacs to read pending output from processes. The output is given to their filter functions. If process is non-
nilthen this function does not return until some output has been received from process.The arguments seconds and millisec let you specify timeout periods. The former specifies a period measured in seconds and the latter specifies one measured in milliseconds. The two time periods thus specified are added together, and
accept-process-outputreturns after that much time, even if there is no subprocess output.The argument millisec is obsolete (and should not be used), because seconds can be floating point to specify waiting a fractional number of seconds. If seconds is 0, the function accepts whatever output is pending but does not wait.
If process is a process, and the argument just-this-one is non-
nil, only output from that process is handled, suspending output from other processes until some output has been received from that process or the timeout expires. If just-this-one is an integer, also inhibit running timers. This feature is generally not recommended, but may be necessary for specific applications, such as speech synthesis.The function
accept-process-outputreturns non-nilif it got output from process, or from any process if process isnil. It returnsnilif the timeout expired before output arrived.
A process sentinel is a function that is called whenever the associated process changes status for any reason, including signals (whether sent by Emacs or caused by the process's own actions) that terminate, stop, or continue the process. The process sentinel is also called if the process exits. The sentinel receives two arguments: the process for which the event occurred, and a string describing the type of event.
If no sentinel function was specified for a process, it will use the default sentinel function, which inserts a message in the process's buffer with the process name and the string describing the event.
The string describing the event looks like one of the following:
"finished\n".
"deleted\n".
"exited abnormally with code exitcode (core dumped)\n".
The “core dumped” part is optional, and only appears if the process
dumped core.
"failed with code fail-code\n".
"signal-description (core dumped)\n". The
signal-description is a system-dependent textual description of
a signal, e.g., "killed" for SIGKILL. The “core
dumped” part is optional, and only appears if the process dumped
core.
"open from host-name\n".
"open\n".
"connection broken by remote peer\n".
A sentinel runs only while Emacs is waiting (e.g., for terminal
input, or for time to elapse, or for process output). This avoids the
timing errors that could result from running sentinels at random places in
the middle of other Lisp programs. A program can wait, so that
sentinels will run, by calling sit-for or sleep-for
(see Waiting), or accept-process-output (see Accepting Output). Emacs also allows sentinels to run when the command loop is
reading input. delete-process calls the sentinel when it
terminates a running process.
Emacs does not keep a queue of multiple reasons to call the sentinel of one process; it records just the current status and the fact that there has been a change. Therefore two changes in status, coming in quick succession, can call the sentinel just once. However, process termination will always run the sentinel exactly once. This is because the process status can't change again after termination.
Emacs explicitly checks for output from the process before running the process sentinel. Once the sentinel runs due to process termination, no further output can arrive from the process.
A sentinel that writes the output into the buffer of the process
should check whether the buffer is still alive. If it tries to insert
into a dead buffer, it will get an error. If the buffer is dead,
(buffer-name (process-buffer process)) returns nil.
Quitting is normally inhibited within a sentinel—otherwise, the
effect of typing C-g at command level or to quit a user command
would be unpredictable. If you want to permit quitting inside a
sentinel, bind inhibit-quit to nil. In most cases, the
right way to do this is with the macro with-local-quit.
See Quitting.
If an error happens during execution of a sentinel, it is caught
automatically, so that it doesn't stop the execution of whatever
programs was running when the sentinel was started. However, if
debug-on-error is non-nil, errors are not caught.
This makes it possible to use the Lisp debugger to debug the
sentinel. See Debugger.
While a sentinel is running, the process sentinel is temporarily
set to nil so that the sentinel won't run recursively.
For this reason it is not possible for a sentinel to specify
a new sentinel.
Note that Emacs automatically saves and restores the match data while executing sentinels. See Match Data.
This function associates sentinel with process. If sentinel is
nil, then the process will have the default sentinel, which inserts a message in the process's buffer when the process status changes.Changes in process sentinels take effect immediately—if the sentinel is slated to be run but has not been called yet, and you specify a new sentinel, the eventual call to the sentinel will use the new one.
(defun msg-me (process event) (princ (format "Process: %s had the event '%s'" process event))) (set-process-sentinel (get-process "shell") 'msg-me) => msg-me (kill-process (get-process "shell")) -| Process: #<process shell> had the event 'killed' => #<process shell>
In case a process status changes need to be passed to several sentinels, you
can use add-function to combine an existing sentinel with a new one.
See Advising Functions.
While a sentinel or filter function is running, this function returns non-
nilif Emacs was waiting for keyboard input from the user at the time the sentinel or filter function was called, ornilif it was not.
When Emacs exits, it terminates all its subprocesses by sending them
the SIGHUP signal. Because subprocesses may be doing
valuable work, Emacs normally asks the user to confirm that it is ok
to terminate them. Each process has a query flag, which, if
non-nil, says that Emacs should ask for confirmation before
exiting and thus killing that process. The default for the query flag
is t, meaning do query.
This function sets the query flag of process to flag. It returns flag.
Here is an example of using
set-process-query-on-exit-flagon a shell process to avoid querying:(set-process-query-on-exit-flag (get-process "shell") nil) => nil
In addition to accessing and manipulating processes that are subprocesses of the current Emacs session, Emacs Lisp programs can also access other processes running on the same machine. We call these system processes, to distinguish them from Emacs subprocesses.
Emacs provides several primitives for accessing system processes.
Not all platforms support these primitives; on those which don't,
these primitives return nil.
This function returns a list of all the processes running on the system. Each process is identified by its PID, a numerical process ID that is assigned by the OS and distinguishes the process from all the other processes running on the same machine at the same time.
This function returns an alist of attributes for the process specified by its process ID pid. Each association in the alist is of the form
(key.value), where key designates the attribute and value is the value of that attribute. The various attribute keys that this function can return are listed below. Not all platforms support all of these attributes; if an attribute is not supported, its association will not appear in the returned alist. Values that are numbers can be either integer or floating point, depending on the magnitude of the value.
euid- The effective user ID of the user who invoked the process. The corresponding value is a number. If the process was invoked by the same user who runs the current Emacs session, the value is identical to what
user-uidreturns (see User Identification).
user- User name corresponding to the process's effective user ID, a string.
egid- The group ID of the effective user ID, a number.
group- Group name corresponding to the effective user's group ID, a string.
comm- The name of the command that runs in the process. This is a string that usually specifies the name of the executable file of the process, without the leading directories. However, some special system processes can report strings that do not correspond to an executable file of a program.
state- The state code of the process. This is a short string that encodes the scheduling state of the process. Here's a list of the most frequently seen codes:
"D"- uninterruptible sleep (usually I/O)
"R"- running
"S"- interruptible sleep (waiting for some event)
"T"- stopped, e.g., by a job control signal
"Z"- zombie: a process that terminated, but was not reaped by its parent
For the full list of the possible states, see the manual page of the ps command.
ppid- The process ID of the parent process, a number.
pgrp- The process group ID of the process, a number.
sess- The session ID of the process. This is a number that is the process ID of the process's session leader.
ttname- A string that is the name of the process's controlling terminal. On Unix and GNU systems, this is normally the file name of the corresponding terminal device, such as /dev/pts65.
tpgid- The numerical process group ID of the foreground process group that uses the process's terminal.
minflt- The number of minor page faults caused by the process since its beginning. (Minor page faults are those that don't involve reading from disk.)
majflt- The number of major page faults caused by the process since its beginning. (Major page faults require a disk to be read, and are thus more expensive than minor page faults.)
cminfltcmajflt- Like
minfltandmajflt, but include the number of page faults for all the child processes of the given process.
utime- Time spent by the process in the user context, for running the application's code. The corresponding value is in the
(highlowmicrosecpicosec)format, the same format used by functionscurrent-time(see current-time) andfile-attributes(see File Attributes).
stime- Time spent by the process in the system (kernel) context, for processing system calls. The corresponding value is in the same format as for
utime.
time- The sum of
utimeandstime. The corresponding value is in the same format as forutime.
cutimecstimectime- Like
utime,stime, andtime, but include the times of all the child processes of the given process.
pri- The numerical priority of the process.
nice- The nice value of the process, a number. (Processes with smaller nice values get scheduled more favorably.)
thcount- The number of threads in the process.
start- The time when the process was started, in the same
(high low microsec picosec)format used byfile-attributesandcurrent-time.
etime- The time elapsed since the process started, in the format
(high low microsec picosec).
vsize- The virtual memory size of the process, measured in kilobytes.
rss- The size of the process's resident set, the number of kilobytes occupied by the process in the machine's physical memory.
pcpu- The percentage of the CPU time used by the process since it started. The corresponding value is a floating-point number between 0 and 100.
pmem- The percentage of the total physical memory installed on the machine used by the process's resident set. The value is a floating-point number between 0 and 100.
args- The command-line with which the process was invoked. This is a string in which individual command-line arguments are separated by blanks; whitespace characters that are embedded in the arguments are quoted as appropriate for the system's shell: escaped by backslash characters on GNU and Unix, and enclosed in double quote characters on Windows. Thus, this command-line string can be directly used in primitives such as
shell-command.
You can use a transaction queue to communicate with a subprocess
using transactions. First use tq-create to create a transaction
queue communicating with a specified process. Then you can call
tq-enqueue to send a transaction.
This function creates and returns a transaction queue communicating with process. The argument process should be a subprocess capable of sending and receiving streams of bytes. It may be a child process, or it may be a TCP connection to a server, possibly on another machine.
This function sends a transaction to queue queue. Specifying the queue has the effect of specifying the subprocess to talk to.
The argument question is the outgoing message that starts the transaction. The argument fn is the function to call when the corresponding answer comes back; it is called with two arguments: closure, and the answer received.
The argument regexp is a regular expression that should match text at the end of the entire answer, but nothing before; that's how
tq-enqueuedetermines where the answer ends.If the argument delay-question is non-
nil, delay sending this question until the process has finished replying to any previous questions. This produces more reliable results with some processes.
Shut down transaction queue queue, waiting for all pending transactions to complete, and then terminate the connection or child process.
Transaction queues are implemented by means of a filter function. See Filter Functions.
Emacs Lisp programs can open stream (TCP) and datagram (UDP) network
connections (see Datagrams) to other processes on the same machine
or other machines.
A network connection is handled by Lisp much like a subprocess, and is
represented by a process object. However, the process you are
communicating with is not a child of the Emacs process, has no
process ID, and you can't kill it or send it signals. All you
can do is send and receive data. delete-process closes the
connection, but does not kill the program at the other end; that
program must decide what to do about closure of the connection.
Lisp programs can listen for connections by creating network servers. A network server is also represented by a kind of process object, but unlike a network connection, the network server never transfers data itself. When it receives a connection request, it creates a new network connection to represent the connection just made. (The network connection inherits certain information, including the process plist, from the server.) The network server then goes back to listening for more connection requests.
Network connections and servers are created by calling
make-network-process with an argument list consisting of
keyword/argument pairs, for example :server t to create a
server process, or :type 'datagram to create a datagram
connection. See Low-Level Network, for details. You can also use
the open-network-stream function described below.
To distinguish the different types of processes, the
process-type function returns the symbol network for a
network connection or server, serial for a serial port
connection, or real for a real subprocess.
The process-status function returns open,
closed, connect, or failed for network
connections. For a network server, the status is always
listen. None of those values is possible for a real
subprocess. See Process Information.
You can stop and resume operation of a network process by calling
stop-process and continue-process. For a server
process, being stopped means not accepting new connections. (Up to 5
connection requests will be queued for when you resume the server; you
can increase this limit, unless it is imposed by the operating
system—see the :server keyword of make-network-process,
Network Processes.) For a network stream connection, being
stopped means not processing input (any arriving input waits until you
resume the connection). For a datagram connection, some number of
packets may be queued but input may be lost. You can use the function
process-command to determine whether a network connection or
server is stopped; a non-nil value means yes.
Emacs can create encrypted network connections, using either built-in
or external support. The built-in support uses the GnuTLS
Transport Layer Security Library; see
the GnuTLS project page.
If your Emacs was compiled with GnuTLS support, the function
gnutls-available-p is defined and returns non-nil. For
more details, see Overview.
The external support uses the starttls.el library, which
requires a helper utility such as gnutls-cli to be installed
on the system. The open-network-stream function can
transparently handle the details of creating encrypted connections for
you, using whatever support is available.
This function opens a TCP connection, with optional encryption, and returns a process object that represents the connection.
The name argument specifies the name for the process object. It is modified as necessary to make it unique.
The buffer argument is the buffer to associate with the connection. Output from the connection is inserted in the buffer, unless you specify your own filter function to handle the output. If buffer is
nil, it means that the connection is not associated with any buffer.The arguments host and service specify where to connect to; host is the host name (a string), and service is the name of a defined network service (a string) or a port number (an integer).
The remaining arguments parameters are keyword/argument pairs that are mainly relevant to encrypted connections:
:nowaitboolean- If non-
nil, try to make an asynchronous connection.
:typetype- The type of connection. Options are:
plain- An ordinary, unencrypted connection.
tlsssl- A TLS (Transport Layer Security) connection.
nilnetwork- Start with a plain connection, and if parameters `:success' and `:capability-command' are supplied, try to upgrade to an encrypted connection via STARTTLS. If that fails, retain the unencrypted connection.
starttls- As for
nil, but if STARTTLS fails drop the connection.
shell- A shell connection.
:always-query-capabilitiesboolean- If non-
nil, always ask for the server's capabilities, even when doing a `plain' connection.
:capability-commandcapability-command- Command string to query the host capabilities.
:end-of-commandregexp:end-of-capabilityregexp- Regular expression matching the end of a command, or the end of the command capability-command. The latter defaults to the former.
:starttls-functionfunction- Function of one argument (the response to capability-command), which returns either
nil, or the command to activate STARTTLS if supported.
:successregexp- Regular expression matching a successful STARTTLS negotiation.
:use-starttls-if-possibleboolean- If non-
nil, do opportunistic STARTTLS upgrades even if Emacs doesn't have built-in TLS support.
:warn-unless-encryptedboolean- If non-
nil, and:return-valueis also non-nil, Emacs will warn if the connection isn't encrypted. This is useful for protocols like IMAP and the like, where most users would expect the network traffic to be encrypted.
:client-certificatelist-or-t- Either a list of the form
(key-file cert-file), naming the certificate key file and certificate file itself, ort, meaning to queryauth-sourcefor this information (see Overview). Only used for TLS or STARTTLS.
:return-listcons-or-nil- The return value of this function. If omitted or
nil, return a process object. Otherwise, a cons of the form(process-object.plist), where plist has keywords:
:greetingstring-or-nil- If non-
nil, the greeting string returned by the host.
:capabilitiesstring-or-nil- If non-
nil, the host's capability string.
:typesymbol- The connection type: `plain' or `tls'.
You create a server by calling make-network-process
(see Network Processes) with :server t. The server will
listen for connection requests from clients. When it accepts a client
connection request, that creates a new network connection, itself a
process object, with the following parameters:
The server's process buffer value is never used directly, but the log function can retrieve it and use it to log connections by inserting text there.
process-contact
keywords :host, :service, :remote.
A datagram connection communicates with individual packets rather
than streams of data. Each call to process-send sends one
datagram packet (see Input to Processes), and each datagram
received results in one call to the filter function.
The datagram connection doesn't have to talk with the same remote
peer all the time. It has a remote peer address which specifies
where to send datagrams to. Each time an incoming datagram is passed
to the filter function, the peer address is set to the address that
datagram came from; that way, if the filter function sends a datagram,
it will go back to that place. You can specify the remote peer
address when you create the datagram connection using the
:remote keyword. You can change it later on by calling
set-process-datagram-address.
If process is a datagram connection or server, this function returns its remote peer address.
If process is a datagram connection or server, this function sets its remote peer address to address.
You can also create network connections by operating at a lower
level than that of open-network-stream, using
make-network-process.
make-network-process
The basic function for creating network connections and network
servers is make-network-process. It can do either of those
jobs, depending on the arguments you give it.
This function creates a network connection or server and returns the process object that represents it. The arguments args are a list of keyword/argument pairs. Omitting a keyword is always equivalent to specifying it with value
nil, except for:coding,:filter-multibyte, and:reuseaddr. Here are the meaningful keywords (those corresponding to network options are listed in the following section):
- :name name
- Use the string name as the process name. It is modified if necessary to make it unique.
- :type type
- Specify the communication type. A value of
nilspecifies a stream connection (the default);datagramspecifies a datagram connection;seqpacketspecifies a sequenced packet stream connection. Both connections and servers can be of these types.
- :server server-flag
- If server-flag is non-
nil, create a server. Otherwise, create a connection. For a stream type server, server-flag may be an integer, which then specifies the length of the queue of pending connections to the server. The default queue length is 5.
- :host host
- Specify the host to connect to. host should be a host name or Internet address, as a string, or the symbol
localto specify the local host. If you specify host for a server, it must specify a valid address for the local host, and only clients connecting to that address will be accepted.
- :service service
- service specifies a port number to connect to; or, for a server, the port number to listen on. It should be a service name that translates to a port number, or an integer specifying the port number directly. For a server, it can also be
t, which means to let the system select an unused port number.
- :family family
- family specifies the address (and protocol) family for communication.
nilmeans determine the proper address family automatically for the given host and service.localspecifies a Unix socket, in which case host is ignored.ipv4andipv6specify to use IPv4 and IPv6, respectively.
- :local local-address
- For a server process, local-address is the address to listen on. It overrides family, host and service, so you might as well not specify them.
- :remote remote-address
- For a connection, remote-address is the address to connect to. It overrides family, host and service, so you might as well not specify them.
For a datagram server, remote-address specifies the initial setting of the remote datagram address.
The format of local-address or remote-address depends on the address family:
- An IPv4 address is represented as a five-element vector of four 8-bit integers and one 16-bit integer
[a b c d p]corresponding to numeric IPv4 address a.b.c.d and port number p.- An IPv6 address is represented as a nine-element vector of 16-bit integers
[a b c d e f g h p]corresponding to numeric IPv6 address a:b:c:d:e:f:g:h and port number p.- A local address is represented as a string, which specifies the address in the local address space.
- An unsupported-family address is represented by a cons
(f.av), where f is the family number and av is a vector specifying the socket address using one element per address data byte. Do not rely on this format in portable code, as it may depend on implementation defined constants, data sizes, and data structure alignment.
- :nowait bool
- If bool is non-
nilfor a stream connection, return without waiting for the connection to complete. When the connection succeeds or fails, Emacs will call the sentinel function, with a second argument matching"open"(if successful) or"failed". The default is to block, so thatmake-network-processdoes not return until the connection has succeeded or failed.
- :stop stopped
- If stopped is non-
nil, start the network connection or server in the stopped state.
- :buffer buffer
- Use buffer as the process buffer.
- :coding coding
- Use coding as the coding system for this process. To specify different coding systems for decoding data from the connection and for encoding data sent to it, specify
(decoding.encoding)for coding.If you don't specify this keyword at all, the default is to determine the coding systems from the data.
- :noquery query-flag
- Initialize the process query flag to query-flag. See Query Before Exit.
- :filter filter
- Initialize the process filter to filter.
- :filter-multibyte multibyte
- If multibyte is non-
nil, strings given to the process filter are multibyte, otherwise they are unibyte. The default is the default value ofenable-multibyte-characters.
- :sentinel sentinel
- Initialize the process sentinel to sentinel.
- :log log
- Initialize the log function of a server process to log. The log function is called each time the server accepts a network connection from a client. The arguments passed to the log function are server, connection, and message; where server is the server process, connection is the new process for the connection, and message is a string describing what has happened.
- :plist plist
- Initialize the process plist to plist.
The original argument list, modified with the actual connection information, is available via the
process-contactfunction.
The following network options can be specified when you create a
network process. Except for :reuseaddr, you can also set or
modify these options later, using set-network-process-option.
For a server process, the options specified with
make-network-process are not inherited by the client
connections, so you will need to set the necessary options for each
child connection as it is created.
network-interface-list), only handle
packets received on that interface. If device-name is nil
(the default), handle packets received on any interface.
Using this option may require special privileges on some systems.
nil for a datagram process, the
process will receive datagram packet sent to a broadcast address, and
be able to send packets to a broadcast address. This is ignored for a stream
connection.
nil, the process can only send
to hosts on the same network as the local host.
nil for a stream connection,
enable exchange of low-level keep-alive messages.
nil, wait for successful
transmission of all queued packets on the connection before it is
deleted (see delete-process). If linger-arg is an
integer, it specifies the maximum time in seconds to wait for queued
packets to be sent before closing the connection. The default is
nil, which means to discard unsent queued packets when the
process is deleted.
nil for a stream connection,
receive out-of-band data in the normal data stream. Otherwise, ignore
out-of-band data.
nil (the default) for a stream
server process, allow this server to reuse a specific port number (see
:service), unless another process on this host is already
listening on that port. If reuseaddr-flag is nil, there
may be a period of time after the last use of that port (by any
process on the host) where it is not possible to make a new server on
that port.
This function sets or modifies a network option for network process process. The accepted options and values are as for
make-network-process. If no-error is non-nil, this function returnsnilinstead of signaling an error if option is not a supported option. If the function successfully completes, it returnst.The current setting of an option is available via the
process-contactfunction.
To test for the availability of a given network feature, use
featurep like this:
(featurep 'make-network-process '(keyword value))
The result of this form is t if it works to specify
keyword with value value in make-network-process.
Here are some of the keyword—value pairs you can test in
this way.
(:nowait t)nil if non-blocking connect is supported.
(:type datagram)nil if datagrams are supported.
(:family local)nil if local (a.k.a. “UNIX domain”) sockets are supported.
(:family ipv6)nil if IPv6 is supported.
(:service t)nil if the system can select the port for a server.
To test for the availability of a given network option, use
featurep like this:
(featurep 'make-network-process 'keyword)
The accepted keyword values are :bindtodevice, etc.
For the complete list, see Network Options. This form returns
non-nil if that particular network option is supported by
make-network-process (or set-network-process-option).
These additional functions are useful for creating and operating on network connections. Note that they are supported only on some systems.
This function returns a list describing the network interfaces of the machine you are using. The value is an alist whose elements have the form
(name.address). address has the same form as the local-address and remote-address arguments tomake-network-process.
This function returns information about the network interface named ifname. The value is a list of the form
(addr bcast netmask hwaddr flags).
- addr
- The Internet protocol address.
- bcast
- The broadcast address.
- netmask
- The network mask.
- hwaddr
- The layer 2 address (Ethernet MAC address, for instance).
- flags
- The current flags of the interface.
This function converts the Lisp representation of a network address to a string.
A five-element vector
[a b c d p]represents an IPv4 address a.b.c.d and port number p.format-network-addressconverts that to the string"a.b.c.d:p".A nine-element vector
[a b c d e f g h p]represents an IPv6 address along with a port number.format-network-addressconverts that to the string"[a:b:c:d:e:f:g:h]:p".If the vector does not include the port number, p, or if omit-port is non-
nil, the result does not include the:p suffix.
Emacs can communicate with serial ports. For interactive use,
M-x serial-term opens a terminal window. In a Lisp program,
make-serial-process creates a process object.
The serial port can be configured at run-time, without having to
close and re-open it. The function serial-process-configure
lets you change the speed, bytesize, and other parameters. In a
terminal window created by serial-term, you can click on the
mode line for configuration.
A serial connection is represented by a process object, which can be
used in a similar way to a subprocess or network process. You can send and
receive data, and configure the serial port. A serial process object
has no process ID, however, and you can't send signals to it, and the
status codes are different from other types of processes.
delete-process on the process object or kill-buffer on
the process buffer close the connection, but this does not affect the
device connected to the serial port.
The function process-type returns the symbol serial
for a process object representing a serial port connection.
Serial ports are available on GNU/Linux, Unix, and MS Windows systems.
Start a terminal-emulator for a serial port in a new buffer. port is the name of the serial port to connect to. For example, this could be /dev/ttyS0 on Unix. On MS Windows, this could be COM1, or \\.\COM10 (double the backslashes in Lisp strings).
speed is the speed of the serial port in bits per second. 9600 is a common value. The buffer is in Term mode; see Term Mode, for the commands to use in that buffer. You can change the speed and the configuration in the mode line menu.
This function creates a process and a buffer. Arguments are specified as keyword/argument pairs. Here's the list of the meaningful keywords, with the first two (port and speed) being mandatory:
:portport- This is the name of the serial port. On Unix and GNU systems, this is a file name such as /dev/ttyS0. On Windows, this could be COM1, or \\.\COM10 for ports higher than COM9 (double the backslashes in Lisp strings).
:speedspeed- The speed of the serial port in bits per second. This function calls
serial-process-configureto handle the speed; see the following documentation of that function for more details.
:namename- The name of the process. If name is not given, port will serve as the process name as well.
:bufferbuffer- The buffer to associate with the process. The value can be either a buffer or a string that names a buffer. Process output goes at the end of that buffer, unless you specify an output stream or filter function to handle the output. If buffer is not given, the process buffer's name is taken from the value of the
:namekeyword.
:codingcoding- If coding is a symbol, it specifies the coding system used for both reading and writing for this process. If coding is a cons
(decoding.encoding), decoding is used for reading, and encoding is used for writing. If not specified, the default is to determine the coding systems from the data itself.
:noqueryquery-flag- Initialize the process query flag to query-flag. See Query Before Exit. The flags defaults to
nilif unspecified.
:stopbool- Start process in the stopped state if bool is non-
nil. In the stopped state, a serial process does not accept incoming data, but you can send outgoing data. The stopped state is cleared bycontinue-processand set bystop-process.
:filterfilter- Install filter as the process filter.
:sentinelsentinel- Install sentinel as the process sentinel.
:plistplist- Install plist as the initial plist of the process.
:bytesize:parity:stopbits:flowcontrol- These are handled by
serial-process-configure, which is called bymake-serial-process.The original argument list, possibly modified by later configuration, is available via the function
process-contact.Here is an example:
(make-serial-process :port "/dev/ttyS0" :speed 9600)
This function configures a serial port connection. Arguments are specified as keyword/argument pairs. Attributes that are not given are re-initialized from the process's current configuration (available via the function
process-contact), or set to reasonable default values. The following arguments are defined:
:processprocess:namename:bufferbuffer:portport- Any of these arguments can be given to identify the process that is to be configured. If none of these arguments is given, the current buffer's process is used.
:speedspeed- The speed of the serial port in bits per second, a.k.a. baud rate. The value can be any number, but most serial ports work only at a few defined values between 1200 and 115200, with 9600 being the most common value. If speed is
nil, the function ignores all other arguments and does not configure the port. This may be useful for special serial ports such as Bluetooth-to-serial converters, which can only be configured through `AT' commands sent through the connection. The value ofnilfor speed is valid only for connections that were already opened by a previous call tomake-serial-processorserial-term.
:bytesizebytesize- The number of bits per byte, which can be 7 or 8. If bytesize is not given or
nil, it defaults to 8.
:parityparity- The value can be
nil(don't use parity), the symbolodd(use odd parity), or the symboleven(use even parity). If parity is not given, it defaults to no parity.
:stopbitsstopbits- The number of stopbits used to terminate a transmission of each byte. stopbits can be 1 or 2. If stopbits is not given or
nil, it defaults to 1.
:flowcontrolflowcontrol- The type of flow control to use for this connection, which is either
nil(don't use flow control), the symbolhw(use RTS/CTS hardware flow control), or the symbolsw(use XON/XOFF software flow control). If flowcontrol is not given, it defaults to no flow control.Internally,
make-serial-processcallsserial-process-configurefor the initial configuration of the serial port.
This section describes how to pack and unpack arrays of bytes,
usually for binary network protocols. These functions convert byte arrays
to alists, and vice versa. The byte array can be represented as a
unibyte string or as a vector of integers, while the alist associates
symbols either with fixed-size objects or with recursive sub-alists.
To use the functions referred to in this section, load the
bindat library.
Conversion from byte arrays to nested alists is also known as deserializing or unpacking, while going in the opposite direction is also known as serializing or packing.
To control unpacking and packing, you write a data layout specification, a special nested list describing named and typed fields. This specification controls the length of each field to be processed, and how to pack or unpack it. We normally keep bindat specs in variables whose names end in `-bindat-spec'; that kind of name is automatically recognized as risky.
A field's type describes the size (in bytes) of the object
that the field represents and, in the case of multibyte fields, how
the bytes are ordered within the field. The two possible orderings
are big endian (also known as “network byte ordering”) and
little endian. For instance, the number #x23cd (decimal
9165) in big endian would be the two bytes #x23 #xcd;
and in little endian, #xcd #x23. Here are the possible
type values:
u8byteu16wordshortu24u32dwordlongu16ru24ru32rstr len
strz len
vec len [type]
(vec len [type]).
ip[127 0 0 1] for localhost.
bits len
8 *
len − 1 and ending with zero. For example: bits
2 unpacks #x28 #x1c to (2 3 4 11 13) and
#x1c #x28 to (3 5 10 11 12).
(eval form)
For a fixed-size field, the length len is given as an integer specifying the number of bytes in the field.
When the length of a field is not fixed, it typically depends on the
value of a preceding field. In this case, the length len can be
given either as a list (name ...) identifying a
field name in the format specified for bindat-get-field
below, or by an expression (eval form) where form
should evaluate to an integer, specifying the field length.
A field specification generally has the form ([name]
handler), where name is optional. Don't use names that
are symbols meaningful as type specifications (above) or handler
specifications (below), since that would be ambiguous. name can
be a symbol or an expression (eval form), in which case
form should evaluate to a symbol.
handler describes how to unpack or pack the field and can be one of the following:
eval form
fill len
align len
struct spec-name
union form (tag spec)...
(eval expr), evaluate
expr with the variable tag dynamically bound to the value
of form. A non-nil result indicates a match.
equal to the value of form.
t.
repeat count field-specs...
eval form is used, it is evaluated just once.
For correct operation, each specification in field-specs must
include a name.
For the (eval form) forms used in a bindat specification,
the form can access and update these dynamically bound variables
during evaluation:
lastbindat-rawbindat-idxbindat-raw) for unpacking or packing.
structbindat-get-field to access specific fields of this structure.
countindexrepeat block, these contain the maximum number of
repetitions (as specified by the count parameter), and the
current repetition number (counting from 0). Setting count to
zero will terminate the inner-most repeat block after the current
repetition has completed.
In the following documentation, spec refers to a data layout
specification, bindat-raw to a byte array, and struct to an
alist representing unpacked field data.
This function unpacks data from the unibyte string or byte array
bindat-rawaccording to spec. Normally, this starts unpacking at the beginning of the byte array, but if bindat-idx is non-nil, it specifies a zero-based starting position to use instead.The value is an alist or nested alist in which each element describes one unpacked field.
This function selects a field's data from the nested alist struct. Usually struct was returned by
bindat-unpack. If name corresponds to just one argument, that means to extract a top-level field value. Multiple name arguments specify repeated lookup of sub-structures. An integer name acts as an array index.For example, if name is
(a b 2 c), that means to find fieldcin the third element of subfieldbof fielda. (This corresponds tostruct.a.b[2].cin C.)
Although packing and unpacking operations change the organization of data (in memory), they preserve the data's total length, which is the sum of all the fields' lengths, in bytes. This value is not generally inherent in either the specification or alist alone; instead, both pieces of information contribute to its calculation. Likewise, the length of a string or array being unpacked may be longer than the data's total length as described by the specification.
This function returns the total length of the data in struct, according to spec.
This function returns a byte array packed according to spec from the data in the alist struct. It normally creates and fills a new byte array starting at the beginning. However, if bindat-raw is non-
nil, it specifies a pre-allocated unibyte string or vector to pack into. If bindat-idx is non-nil, it specifies the starting offset for packing intobindat-raw.When pre-allocating, you should make sure
(lengthbindat-raw)meets or exceeds the total length to avoid an out-of-range error.
Convert the Internet address vector ip to a string in the usual dotted notation.
(bindat-ip-to-string [127 0 0 1]) => "127.0.0.1"
Here is a complete example of byte unpacking and packing:
(require 'bindat)
(defvar fcookie-index-spec
'((:version u32)
(:count u32)
(:longest u32)
(:shortest u32)
(:flags u32)
(:delim u8)
(:ignored fill 3)
(:offset repeat (:count) (:foo u32)))
"Description of a fortune cookie index file's contents.")
(defun fcookie (cookies &optional index)
"Display a random fortune cookie from file COOKIES.
Optional second arg INDEX specifies the associated index
filename, by default \"COOKIES.dat\". Display cookie text
in buffer \"*Fortune Cookie: BASENAME*\", where BASENAME
is COOKIES without the directory part."
(interactive "fCookies file: ")
(let* ((info (with-temp-buffer
(insert-file-contents-literally
(or index (concat cookies ".dat")))
(bindat-unpack fcookie-index-spec
(buffer-string))))
(sel (random (bindat-get-field info :count)))
(beg (cdar (bindat-get-field info :offset sel)))
(end (or (cdar (bindat-get-field info
:offset (1+ sel)))
(nth 7 (file-attributes cookies)))))
(switch-to-buffer
(get-buffer-create
(format "*Fortune Cookie: %s*"
(file-name-nondirectory cookies))))
(erase-buffer)
(insert-file-contents-literally
cookies nil beg (- end 3))))
(defun fcookie-create-index (cookies &optional index delim)
"Scan file COOKIES, and write out its index file.
Optional arg INDEX specifies the index filename, which by
default is \"COOKIES.dat\". Optional arg DELIM specifies the
unibyte character that, when found on a line of its own in
COOKIES, indicates the border between entries."
(interactive "fCookies file: ")
(setq delim (or delim ?%))
(let ((delim-line (format "\n%c\n" delim))
(count 0)
(max 0)
min p q len offsets)
(unless (= 3 (string-bytes delim-line))
(error "Delimiter cannot be represented in one byte"))
(with-temp-buffer
(insert-file-contents-literally cookies)
(while (and (setq p (point))
(search-forward delim-line (point-max) t)
(setq len (- (point) 3 p)))
(setq count (1+ count)
max (max max len)
min (min (or min max) len)
offsets (cons (1- p) offsets))))
(with-temp-buffer
(set-buffer-multibyte nil)
(insert
(bindat-pack
fcookie-index-spec
`((:version . 2)
(:count . ,count)
(:longest . ,max)
(:shortest . ,min)
(:flags . 0)
(:delim . ,delim)
(:offset . ,(mapcar (lambda (o)
(list (cons :foo o)))
(nreverse offsets))))))
(let ((coding-system-for-write 'raw-text-unix))
(write-file (or index (concat cookies ".dat")))))))
The following is an example of defining and unpacking a complex structure. Consider the following C structures:
struct header {
unsigned long dest_ip;
unsigned long src_ip;
unsigned short dest_port;
unsigned short src_port;
};
struct data {
unsigned char type;
unsigned char opcode;
unsigned short length; /* in network byte order */
unsigned char id[8]; /* null-terminated string */
unsigned char data[/* (length + 3) & ~3 */];
};
struct packet {
struct header header;
unsigned long counters[2]; /* in little endian order */
unsigned char items;
unsigned char filler[3];
struct data item[/* items */];
};
The corresponding data layout specification is:
(setq header-spec
'((dest-ip ip)
(src-ip ip)
(dest-port u16)
(src-port u16)))
(setq data-spec
'((type u8)
(opcode u8)
(length u16) ; network byte order
(id strz 8)
(data vec (length))
(align 4)))
(setq packet-spec
'((header struct header-spec)
(counters vec 2 u32r) ; little endian order
(items u8)
(fill 3)
(item repeat (items)
(struct data-spec))))
A binary data representation is:
(setq binary-data
[ 192 168 1 100 192 168 1 101 01 28 21 32
160 134 1 0 5 1 0 0 2 0 0 0
2 3 0 5 ?A ?B ?C ?D ?E ?F 0 0 1 2 3 4 5 0 0 0
1 4 0 7 ?B ?C ?D ?E ?F ?G 0 0 6 7 8 9 10 11 12 0 ])
The corresponding decoded structure is:
(setq decoded (bindat-unpack packet-spec binary-data))
=>
((header
(dest-ip . [192 168 1 100])
(src-ip . [192 168 1 101])
(dest-port . 284)
(src-port . 5408))
(counters . [100000 261])
(items . 2)
(item ((data . [1 2 3 4 5])
(id . "ABCDEF")
(length . 5)
(opcode . 3)
(type . 2))
((data . [6 7 8 9 10 11 12])
(id . "BCDEFG")
(length . 7)
(opcode . 4)
(type . 1))))
An example of fetching data from this structure:
(bindat-get-field decoded 'item 1 'id)
=> "BCDEFG"
This chapter describes a number of features related to the display that Emacs presents to the user.
The function redraw-frame clears and redisplays the entire
contents of a given frame (see Frames). This is useful if the
screen is corrupted.
This function clears and redisplays frame frame. If frame is omitted or nil, it redraws the selected frame.
Even more powerful is redraw-display:
In Emacs, processing user input takes priority over redisplay. If you call these functions when input is available, they don't redisplay immediately, but the requested redisplay does happen eventually—after all the input has been processed.
On text terminals, suspending and resuming Emacs normally also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption.
This variable controls whether Emacs redraws the entire screen after it has been suspended and resumed. Non-
nilmeans there is no need to redraw,nilmeans redrawing is needed. The default isnil.
Emacs normally tries to redisplay the screen whenever it waits for input. With the following function, you can request an immediate attempt to redisplay, in the middle of Lisp code, without actually waiting for input.
This function tries immediately to redisplay. The optional argument force, if non-
nil, forces the redisplay to be performed, instead of being preempted if input is pending.The function returns
tif it actually tried to redisplay, andnilotherwise. A value oftdoes not mean that redisplay proceeded to completion; it could have been preempted by newly arriving input.
Although redisplay tries immediately to redisplay, it does
not change how Emacs decides which parts of its frame(s) to redisplay.
By contrast, the following function adds certain windows to the
pending redisplay work (as if their contents had completely changed),
but does not immediately try to perform redisplay.
This function forces some or all windows to be updated the next time Emacs does a redisplay. If object is a window, that window is to be updated. If object is a buffer or buffer name, all windows displaying that buffer are to be updated. If object is
nil(or omitted), all windows are to be updated.This function does not do a redisplay immediately; Emacs does that as it waits for input, or when the function
redisplayis called.
A function run just before redisplay. It is called with one argument, the set of windows to be redisplayed. The set can be
nil, meaning only the selected window, ort, meaning all the windows.
This hook is run just before redisplay. It is called once in each window that is about to be redisplayed, with
current-bufferset to the buffer displayed in that window.
When a line of text extends beyond the right edge of a window, Emacs can continue the line (make it wrap to the next screen line), or truncate the line (limit it to one screen line). The additional screen lines used to display a long text line are called continuation lines. Continuation is not the same as filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. See Filling.
On a graphical display, tiny arrow images in the window fringes indicate truncated and continued lines (see Fringes). On a text terminal, a `$' in the rightmost column of the window indicates truncation; a `\' on the rightmost column indicates a line that wraps. (The display table can specify alternate characters to use for this; see Display Tables).
If this buffer-local variable is non-
nil, lines that extend beyond the right edge of the window are truncated; otherwise, they are continued. As a special exception, the variabletruncate-partial-width-windowstakes precedence in partial-width windows (i.e., windows that do not occupy the entire frame width).
This variable controls line truncation in partial-width windows. A partial-width window is one that does not occupy the entire frame width (see Splitting Windows). If the value is
nil, line truncation is determined by the variabletruncate-lines(see above). If the value is an integer n, lines are truncated if the partial-width window has fewer than n columns, regardless of the value oftruncate-lines; if the partial-width window has n or more columns, line truncation is determined bytruncate-lines. For any other non-nilvalue, lines are truncated in every partial-width window, regardless of the value oftruncate-lines.
When horizontal scrolling (see Horizontal Scrolling) is in use in a window, that forces truncation.
If this buffer-local variable is non-
nil, it defines a wrap prefix which Emacs displays at the start of every continuation line. (If lines are truncated,wrap-prefixis never used.) Its value may be a string or an image (see Other Display Specs), or a stretch of whitespace such as specified by the:widthor:align-todisplay properties (see Specified Space). The value is interpreted in the same way as adisplaytext property. See Display Property.A wrap prefix may also be specified for regions of text, using the
wrap-prefixtext or overlay property. This takes precedence over thewrap-prefixvariable. See Special Properties.
If this buffer-local variable is non-
nil, it defines a line prefix which Emacs displays at the start of every non-continuation line. Its value may be a string or an image (see Other Display Specs), or a stretch of whitespace such as specified by the:widthor:align-todisplay properties (see Specified Space). The value is interpreted in the same way as adisplaytext property. See Display Property.A line prefix may also be specified for regions of text using the
line-prefixtext or overlay property. This takes precedence over theline-prefixvariable. See Special Properties.
The echo area is used for displaying error messages
(see Errors), for messages made with the message primitive,
and for echoing keystrokes. It is not the same as the minibuffer,
despite the fact that the minibuffer appears (when active) in the same
place on the screen as the echo area. See The Minibuffer.
Apart from the functions documented in this section, you can print
Lisp objects to the echo area by specifying t as the output
stream. See Output Streams.
This section describes the standard functions for displaying messages in the echo area.
This function displays a message in the echo area. format-string is a format string, and arguments are the objects for its format specifications, like in the
format-messagefunction (see Formatting Strings). The resulting formatted string is displayed in the echo area; if it containsfacetext properties, it is displayed with the specified faces (see Faces). The string is also added to the *Messages* buffer, but without text properties (see Logging Messages).The
text-quoting-stylevariable controls what quotes are generated; See Keys in Documentation. A call using a format like "Missing `%s'" with grave accents and apostrophes typically generates a message like "Missing ‘foo’" with matching curved quotes. In contrast, a call using a format like "Missing '%s'" with only apostrophes typically generates a message like "Missing ’foo’" with only closing curved quotes, an unusual style in English.In batch mode, the message is printed to the standard error stream, followed by a newline.
When
inhibit-messageis non-nil, no message will be displayed in the echo area, it will only be logged to `*Messages*'.If format-string is
nilor the empty string,messageclears the echo area; if the echo area has been expanded automatically, this brings it back to its normal size. If the minibuffer is active, this brings the minibuffer contents back onto the screen immediately.(message "Reverting `%s'..." (buffer-name)) -| Reverting ‘subr.el’... => "Reverting ‘subr.el’..." ---------- Echo Area ---------- Reverting ‘subr.el’... ---------- Echo Area ----------To automatically display a message in the echo area or in a pop-buffer, depending on its size, use
display-message-or-buffer(see below).Warning: If you want to use your own string as a message verbatim, don't just write
(messagestring). If string contains `%', ``', or `'' it may be reformatted, with undesirable results. Instead, use(message "%s"string).
When this variable is non-
nil,messageand related functions will not use the Echo Area to display messages.
This construct displays a message in the echo area temporarily, during the execution of body. It displays message, executes body, then returns the value of the last body form while restoring the previous echo area contents.
This function displays a message like
message, but may display it in a dialog box instead of the echo area. If this function is called in a command that was invoked using the mouse—more precisely, iflast-nonmenu-event(see Command Loop Info) is eithernilor a list—then it uses a dialog box or pop-up menu to display the message. Otherwise, it uses the echo area. (This is the same criterion thaty-or-n-puses to make a similar decision; see Yes-or-No Queries.)You can force use of the mouse or of the echo area by binding
last-nonmenu-eventto a suitable value around the call.
This function displays a message like
message, but uses a dialog box (or a pop-up menu) whenever that is possible. If it is impossible to use a dialog box or pop-up menu, because the terminal does not support them, thenmessage-boxuses the echo area, likemessage.
This function displays the message message, which may be either a string or a buffer. If it is shorter than the maximum height of the echo area, as defined by
max-mini-window-height, it is displayed in the echo area, usingmessage. Otherwise,display-bufferis used to show it in a pop-up buffer.Returns either the string shown in the echo area, or when a pop-up buffer is used, the window used to display it.
If message is a string, then the optional argument buffer-name is the name of the buffer used to display it when a pop-up buffer is used, defaulting to *Message*. In the case where message is a string and displayed in the echo area, it is not specified whether the contents are inserted into the buffer anyway.
The optional arguments action and frame are as for
display-buffer, and only used if a buffer is displayed.
This function returns the message currently being displayed in the echo area, or
nilif there is none.
When an operation can take a while to finish, you should inform the user about the progress it makes. This way the user can estimate remaining time and clearly see that Emacs is busy working, not hung. A convenient way to do this is to use a progress reporter.
Here is a working example that does nothing useful:
(let ((progress-reporter
(make-progress-reporter "Collecting mana for Emacs..."
0 500)))
(dotimes (k 500)
(sit-for 0.01)
(progress-reporter-update progress-reporter k))
(progress-reporter-done progress-reporter))
This function creates and returns a progress reporter object, which you will use as an argument for the other functions listed below. The idea is to precompute as much data as possible to make progress reporting very fast.
When this progress reporter is subsequently used, it will display message in the echo area, followed by progress percentage. message is treated as a simple string. If you need it to depend on a filename, for instance, use
format-messagebefore calling this function.The arguments min-value and max-value should be numbers standing for the starting and final states of the operation. For instance, an operation that scans a buffer should set these to the results of
point-minandpoint-maxcorrespondingly. max-value should be greater than min-value.Alternatively, you can set min-value and max-value to
nil. In that case, the progress reporter does not report process percentages; it instead displays a “spinner” that rotates a notch each time you update the progress reporter.If min-value and max-value are numbers, you can give the argument current-value a numerical value specifying the initial progress; if omitted, this defaults to min-value.
The remaining arguments control the rate of echo area updates. The progress reporter will wait for at least min-change more percents of the operation to be completed before printing next message; the default is one percent. min-time specifies the minimum time in seconds to pass between successive prints; the default is 0.2 seconds. (On some operating systems, the progress reporter may handle fractions of seconds with varying precision).
This function calls
progress-reporter-update, so the first message is printed immediately.
This function does the main work of reporting progress of your operation. It displays the message of reporter, followed by progress percentage determined by value. If percentage is zero, or close enough according to the min-change and min-time arguments, then it is omitted from the output.
reporter must be the result of a call to
make-progress-reporter. value specifies the current state of your operation and must be between min-value and max-value (inclusive) as passed tomake-progress-reporter. For instance, if you scan a buffer, then value should be the result of a call topoint.This function respects min-change and min-time as passed to
make-progress-reporterand so does not output new messages on every invocation. It is thus very fast and normally you should not try to reduce the number of calls to it: resulting overhead will most likely negate your effort.
This function is similar to
progress-reporter-updateexcept that it prints a message in the echo area unconditionally.The first two arguments have the same meaning as for
progress-reporter-update. Optional new-message allows you to change the message of the reporter. Since this function always updates the echo area, such a change will be immediately presented to the user.
This function should be called when the operation is finished. It prints the message of reporter followed by word `done' in the echo area.
You should always call this function and not hope for
progress-reporter-updateto print `100%'. Firstly, it may never print it, there are many good reasons for this not to happen. Secondly, `done' is more explicit.
This is a convenience macro that works the same way as
dotimesdoes, but also reports loop progress using the functions described above. It allows you to save some typing.You can rewrite the example in the beginning of this node using this macro this way:
(dotimes-with-progress-reporter (k 500) "Collecting some mana for Emacs..." (sit-for 0.01))
Almost all the messages displayed in the echo area are also recorded
in the *Messages* buffer so that the user can refer back to
them. This includes all the messages that are output with
message. By default, this buffer is read-only and uses the major
mode messages-buffer-mode. Nothing prevents the user from
killing the *Messages* buffer, but the next display of a message
recreates it. Any Lisp code that needs to access the
*Messages* buffer directly and wants to ensure that it exists
should use the function messages-buffer.
This function returns the *Messages* buffer. If it does not exist, it creates it, and switches it to
messages-buffer-mode.
This variable specifies how many lines to keep in the *Messages* buffer. The value
tmeans there is no limit on how many lines to keep. The valuenildisables message logging entirely. Here's how to display a message and prevent it from being logged:(let (message-log-max) (message ...))
To make *Messages* more convenient for the user, the logging facility combines successive identical messages. It also combines successive related messages for the sake of two cases: question followed by answer, and a series of progress messages.
A question followed by an answer has two messages like the
ones produced by y-or-n-p: the first is `question',
and the second is `question...answer'. The first
message conveys no additional information beyond what's in the second,
so logging the second message discards the first from the log.
A series of progress messages has successive messages like
those produced by make-progress-reporter. They have the form
`base...how-far', where base is the same each
time, while how-far varies. Logging each message in the series
discards the previous one, provided they are consecutive.
The functions make-progress-reporter and y-or-n-p
don't have to do anything special to activate the message log
combination feature. It operates whenever two consecutive messages
are logged that share a common prefix ending in `...'.
These variables control details of how the echo area works.
This variable controls where the cursor appears when a message is displayed in the echo area. If it is non-
nil, then the cursor appears at the end of the message. Otherwise, the cursor appears at point—not in the echo area at all.The value is normally
nil; Lisp programs bind it totfor brief periods of time.
This normal hook is run whenever the echo area is cleared—either by
(message nil)or for any other reason.
This variable determines how much time should elapse before command characters echo. Its value must be a number, and specifies the number of seconds to wait before echoing. If the user types a prefix key (such as C-x) and then delays this many seconds before continuing, the prefix key is echoed in the echo area. (Once echoing begins in a key sequence, all subsequent characters in the same key sequence are echoed immediately.)
If the value is zero, then command input is not echoed.
Normally, displaying a long message resizes the echo area to display the entire message. But if the variable
message-truncate-linesis non-nil, the echo area does not resize, and the message is truncated to fit it.
The variable max-mini-window-height, which specifies the
maximum height for resizing minibuffer windows, also applies to the
echo area (which is really a special use of the minibuffer window;
see Minibuffer Misc).
Warnings are a facility for a program to inform the user of a possible problem, but continue running.
Every warning has a textual message, which explains the problem for the user, and a severity level which is a symbol. Here are the possible severity levels, in order of decreasing severity, and their meanings:
:emergency:error:warning:debugWhen your program encounters invalid input data, it can either
signal a Lisp error by calling error or signal or report
a warning with severity :error. Signaling a Lisp error is the
easiest thing to do, but it means the program cannot continue
processing. If you want to take the trouble to implement a way to
continue processing despite the bad data, then reporting a warning of
severity :error is the right way to inform the user of the
problem. For instance, the Emacs Lisp byte compiler can report an
error that way and continue compiling other functions. (If the
program signals a Lisp error and then handles it with
condition-case, the user won't see the error message; it could
show the message to the user by reporting it as a warning.)
Each warning has a warning type to classify it. The type is a
list of symbols. The first symbol should be the custom group that you
use for the program's user options. For example, byte compiler
warnings use the warning type (bytecomp). You can also
subcategorize the warnings, if you wish, by using more symbols in the
list.
This function reports a warning, using message as the message and type as the warning type. level should be the severity level, with
:warningbeing the default.buffer-name, if non-
nil, specifies the name of the buffer for logging the warning. By default, it is *Warnings*.
This function reports a warning using the value of
(format-messagemessage args...)as the message in the *Warnings* buffer. In other respects it is equivalent todisplay-warning.
This function reports a warning using the value of
(format-messagemessage args...)as the message,(emacs)as the type, and:warningas the severity level. It exists for compatibility only; we recommend not using it, because you should specify a specific warning type.
Programs can customize how their warnings appear by binding the variables described in this section.
This list defines the meaning and severity order of the warning severity levels. Each element defines one severity level, and they are arranged in order of decreasing severity.
Each element has the form
(level string function), where level is the severity level it defines. string specifies the textual description of this level. string should use `%s' to specify where to put the warning type information, or it can omit the `%s' so as not to include that information.The optional function, if non-
nil, is a function to call with no arguments, to get the user's attention.Normally you should not change the value of this variable.
If non-
nil, the value is a function to generate prefix text for warnings. Programs can bind the variable to a suitable function.display-warningcalls this function with the warnings buffer current, and the function can insert text in it. That text becomes the beginning of the warning message.The function is called with two arguments, the severity level and its entry in
warning-levels. It should return a list to use as the entry (this value need not be an actual member ofwarning-levels). By constructing this value, the function can change the severity of the warning, or specify different handling for a given severity level.If the variable's value is
nilthen there is no function to call.
Programs can bind this variable to
tto say that the next warning should begin a series. When several warnings form a series, that means to leave point on the first warning of the series, rather than keep moving it for each warning so that it appears on the last one. The series ends when the local binding is unbound andwarning-seriesbecomesnilagain.The value can also be a symbol with a function definition. That is equivalent to
t, except that the next warning will also call the function with no arguments with the warnings buffer current. The function can insert text which will serve as a header for the series of warnings.Once a series has begun, the value is a marker which points to the buffer position in the warnings buffer of the start of the series.
The variable's normal value is
nil, which means to handle each warning separately.
When this variable is non-
nil, it specifies a fill prefix to use for filling each warning's text.
This variable specifies the format for displaying the warning type in the warning message. The result of formatting the type this way gets included in the message under the control of the string in the entry in
warning-levels. The default value is" (%s)". If you bind it to""then the warning type won't appear at all.
These variables are used by users to control what happens when a Lisp program reports a warning.
This user option specifies the minimum severity level that should be shown immediately to the user. The default is
:warning, which means to immediately display all warnings except:debugwarnings.
This user option specifies the minimum severity level that should be logged in the warnings buffer. The default is
:warning, which means to log all warnings except:debugwarnings.
This list specifies which warning types should not be displayed immediately for the user. Each element of the list should be a list of symbols. If its elements match the first elements in a warning type, then that warning is not displayed immediately.
This list specifies which warning types should not be logged in the warnings buffer. Each element of the list should be a list of symbols. If it matches the first few elements in a warning type, then that warning is not logged.
Sometimes, you may wish to avoid showing a warning while a command is
running, and only show it only after the end of the command. You can
use the variable delayed-warnings-list for this.
The value of this variable is a list of warnings to be displayed after the current command has finished. Each element must be a list
(type message [level [buffer-name]])with the same form, and the same meanings, as the argument list of
display-warning(see Warning Basics). Immediately after runningpost-command-hook(see Command Overview), the Emacs command loop displays all the warnings specified by this variable, then resets it tonil.
Programs which need to further customize the delayed warnings
mechanism can change the variable delayed-warnings-hook:
This is a normal hook which is run by the Emacs command loop, after
post-command-hook, in order to to process and display delayed warnings.Its default value is a list of two functions:
(collapse-delayed-warnings display-delayed-warnings)The function
collapse-delayed-warningsremoves repeated entries fromdelayed-warnings-list. The functiondisplay-delayed-warningscallsdisplay-warningon each of the entries indelayed-warnings-list, in turn, and then setsdelayed-warnings-listtonil.
You can make characters invisible, so that they do not appear on
the screen, with the invisible property. This can be either a
text property (see Text Properties) or an overlay property
(see Overlays). Cursor motion also partly ignores these
characters; if the command loop finds that point is inside a range of
invisible text after a command, it relocates point to the other side
of the text.
In the simplest case, any non-nil invisible property makes
a character invisible. This is the default case—if you don't alter
the default value of buffer-invisibility-spec, this is how the
invisible property works. You should normally use t
as the value of the invisible property if you don't plan
to set buffer-invisibility-spec yourself.
More generally, you can use the variable buffer-invisibility-spec
to control which values of the invisible property make text
invisible. This permits you to classify the text into different subsets
in advance, by giving them different invisible values, and
subsequently make various subsets visible or invisible by changing the
value of buffer-invisibility-spec.
Controlling visibility with buffer-invisibility-spec is
especially useful in a program to display the list of entries in a
database. It permits the implementation of convenient filtering
commands to view just a part of the entries in the database. Setting
this variable is very fast, much faster than scanning all the text in
the buffer looking for properties to change.
This variable specifies which kinds of
invisibleproperties actually make a character invisible. Setting this variable makes it buffer-local.
t- A character is invisible if its
invisibleproperty is non-nil. This is the default.
- a list
- Each element of the list specifies a criterion for invisibility; if a character's
invisibleproperty fits any one of these criteria, the character is invisible. The list can have two kinds of elements:
- atom
- A character is invisible if its
invisibleproperty value is atom or if it is a list with atom as a member; comparison is done witheq.
(atom. t)- A character is invisible if its
invisibleproperty value is atom or if it is a list with atom as a member; comparison is done witheq. Moreover, a sequence of such characters displays as an ellipsis.
Two functions are specifically provided for adding elements to
buffer-invisibility-spec and removing elements from it.
This function adds the element element to
buffer-invisibility-spec. Ifbuffer-invisibility-specwast, it changes to a list,(t), so that text whoseinvisibleproperty istremains invisible.
This removes the element element from
buffer-invisibility-spec. This does nothing if element is not in the list.
A convention for use of buffer-invisibility-spec is that a
major mode should use the mode's own name as an element of
buffer-invisibility-spec and as the value of the
invisible property:
;; If you want to display an ellipsis: (add-to-invisibility-spec '(my-symbol . t)) ;; If you don't want ellipsis: (add-to-invisibility-spec 'my-symbol) (overlay-put (make-overlay beginning end) 'invisible 'my-symbol) ;; When done with the invisibility: (remove-from-invisibility-spec '(my-symbol . t)) ;; Or respectively: (remove-from-invisibility-spec 'my-symbol)
You can check for invisibility using the following function:
If pos-or-prop is a marker or number, this function returns a non-
nilvalue if the text at that position is invisible.If pos-or-prop is any other kind of Lisp object, that is taken to mean a possible value of the
invisibletext or overlay property. In that case, this function returns a non-nilvalue if that value would cause text to become invisible, based on the current value ofbuffer-invisibility-spec.
Ordinarily, functions that operate on text or move point do not care
whether the text is invisible, they process invisible characters and
visible characters alike. The user-level line motion commands,
such as next-line, previous-line, ignore invisible
newlines if line-move-ignore-invisible is non-nil (the
default), i.e., behave like these invisible newlines didn't exist in
the buffer, but only because they are explicitly programmed to do so.
If a command ends with point inside or at the boundary of
invisible text, the main editing loop relocates point to one of the
two ends of the invisible text. Emacs chooses the direction of
relocation so that it is the same as the overall movement direction of
the command; if in doubt, it prefers a position where an inserted char
would not inherit the invisible property. Additionally, if the
text is not replaced by an ellipsis and the command only moved within
the invisible text, then point is moved one extra character so as to
try and reflect the command's movement by a visible movement of the
cursor.
Thus, if the command moved point back to an invisible range (with the usual stickiness), Emacs moves point back to the beginning of that range. If the command moved point forward into an invisible range, Emacs moves point forward to the first visible character that follows the invisible text and then forward one more character.
These adjustments of point that ended up in the middle of
invisible text can be disabled by setting disable-point-adjustment
to a non-nil value. See Adjusting Point.
Incremental search can make invisible overlays visible temporarily
and/or permanently when a match includes invisible text. To enable
this, the overlay should have a non-nil
isearch-open-invisible property. The property value should be a
function to be called with the overlay as an argument. This function
should make the overlay visible permanently; it is used when the match
overlaps the overlay on exit from the search.
During the search, such overlays are made temporarily visible by
temporarily modifying their invisible and intangible properties. If you
want this to be done differently for a certain overlay, give it an
isearch-open-invisible-temporary property which is a function.
The function is called with two arguments: the first is the overlay, and
the second is nil to make the overlay visible, or t to
make it invisible again.
Selective display refers to a pair of related features for hiding certain lines on the screen.
The first variant, explicit selective display, was designed for use in a Lisp
program: it controls which lines are hidden by altering the text. This kind of
hiding is now obsolete; instead you can get the same effect with the
invisible property (see Invisible Text).
In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be a user-level feature.
The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text that was formerly a line following that newline is now hidden. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line.
Selective display does not directly affect editing commands. For
example, C-f (forward-char) moves point unhesitatingly
into hidden text. However, the replacement of newline characters with
carriage return characters affects some editing commands. For
example, next-line skips hidden lines, since it searches only
for newlines. Modes that use selective display can also define
commands that take account of the newlines, or that control which
parts of the text are hidden.
When you write a selectively displayed buffer into a file, all the control-m's are output as newlines. This means that when you next read in the file, it looks OK, with nothing hidden. The selective display effect is seen only within Emacs.
This buffer-local variable enables selective display. This means that lines, or portions of lines, may be made hidden.
- If the value of
selective-displayist, then the character control-m marks the start of hidden text; the control-m, and the rest of the line following it, are not displayed. This is explicit selective display.- If the value of
selective-displayis a positive integer, then lines that start with more than that many columns of indentation are not displayed.When some portion of a buffer is hidden, the vertical movement commands operate as if that portion did not exist, allowing a single
next-linecommand to skip any number of hidden lines. However, character movement commands (such asforward-char) do not skip the hidden portion, and it is possible (if tricky) to insert or delete text in an hidden portion.In the examples below, we show the display appearance of the buffer
foo, which changes with the value ofselective-display. The contents of the buffer do not change.(setq selective-display nil) => nil ---------- Buffer: foo ---------- 1 on this column 2on this column 3n this column 3n this column 2on this column 1 on this column ---------- Buffer: foo ---------- (setq selective-display 2) => 2 ---------- Buffer: foo ---------- 1 on this column 2on this column 2on this column 1 on this column ---------- Buffer: foo ----------
If this buffer-local variable is non-
nil, then Emacs displays `...' at the end of a line that is followed by hidden text. This example is a continuation of the previous one.(setq selective-display-ellipses t) => t ---------- Buffer: foo ---------- 1 on this column 2on this column ... 2on this column 1 on this column ---------- Buffer: foo ----------You can use a display table to substitute other text for the ellipsis (`...'). See Display Tables.
Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many help commands use this feature.
This function executes the forms in body while arranging to insert any output they print into the buffer named buffer-name, which is first created if necessary, and put into Help mode. (See the similar form
with-temp-buffer-windowbelow.) Finally, the buffer is displayed in some window, but that window is not selected.If the forms in body do not change the major mode in the output buffer, so that it is still Help mode at the end of their execution, then
with-output-to-temp-buffermakes this buffer read-only at the end, and also scans it for function and variable names to make them into clickable cross-references. See Tips for Documentation Strings, in particular the item on hyperlinks in documentation strings, for more details.The string buffer-name specifies the temporary buffer, which need not already exist. The argument must be a string, not a buffer. The buffer is erased initially (with no questions asked), and it is marked as unmodified after
with-output-to-temp-bufferexits.
with-output-to-temp-bufferbindsstandard-outputto the temporary buffer, then it evaluates the forms in body. Output using the Lisp output functions within body goes by default to that buffer (but screen display and messages in the echo area, although they are “output” in the general sense of the word, are not affected). See Output Functions.Several hooks are available for customizing the behavior of this construct; they are listed below.
The value of the last form in body is returned.
---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ---------- (with-output-to-temp-buffer "foo" (print 20) (print standard-output)) => #<buffer foo> ---------- Buffer: foo ---------- 20 #<buffer foo> ---------- Buffer: foo ----------
If this variable is non-
nil,with-output-to-temp-buffercalls it as a function to do the job of displaying a help buffer. The function gets one argument, which is the buffer it should display.It is a good idea for this function to run
temp-buffer-show-hookjust aswith-output-to-temp-buffernormally would, inside ofsave-selected-windowand with the chosen window and buffer selected.
This normal hook is run by
with-output-to-temp-bufferbefore evaluating body. When the hook runs, the temporary buffer is current. This hook is normally set up with a function to put the buffer in Help mode.
This normal hook is run by
with-output-to-temp-bufferafter displaying the temporary buffer. When the hook runs, the temporary buffer is current, and the window it was displayed in is selected.
This macro is similar to
with-output-to-temp-buffer. Like that construct, it executes body while arranging to insert any output it prints into the buffer named buffer-or-name and displays that buffer in some window. Unlikewith-output-to-temp-buffer, however, it does not automatically switch that buffer to Help mode.The argument buffer-or-name specifies the temporary buffer. It can be either a buffer, which must already exist, or a string, in which case a buffer of that name is created, if necessary. The buffer is marked as unmodified and read-only when
with-temp-buffer-windowexits.This macro does not call
temp-buffer-show-function. Rather, it passes the action argument todisplay-buffer(see Choosing Window) in order to display the buffer.The value of the last form in body is returned, unless the argument quit-function is specified. In that case, it is called with two arguments: the window showing the buffer and the result of body. The final return value is then whatever quit-function returns.
This macro uses the normal hooks
temp-buffer-window-setup-hookandtemp-buffer-window-show-hookin place of the analogous hooks run bywith-output-to-temp-buffer.
The two constructs described next are mostly identical to
with-temp-buffer-window but differ from it as specified:
This macro is like
with-temp-buffer-windowbut unlike that makes the buffer specified by buffer-or-name current for running body.
This macro is like
with-current-buffer-windowbut unlike that displays the buffer specified by buffer-or-name before running body.
A window showing a temporary buffer can be fit to the size of that buffer using the following mode:
When this minor mode is enabled, windows showing a temporary buffer are automatically resized to fit their buffer's contents.
A window is resized if and only if it has been specially created for the buffer. In particular, windows that have shown another buffer before are not resized. By default, this mode uses
fit-window-to-buffer(see Resizing Windows) for resizing. You can specify a different function by customizing the optionstemp-buffer-max-heightandtemp-buffer-max-widthbelow.
This option specifies the maximum height (in lines) of a window displaying a temporary buffer when
temp-buffer-resize-modeis enabled. It can also be a function to be called to choose the height for such a buffer. It gets one argument, the buffer, and should return a positive integer. At the time the function is called, the window to be resized is selected.
This option specifies the maximum width of a window (in columns) displaying a temporary buffer when
temp-buffer-resize-modeis enabled. It can also be a function to be called to choose the width for such a buffer. It gets one argument, the buffer, and should return a positive integer. At the time the function is called, the window to be resized is selected.
The following function uses the current buffer for temporal display:
This function momentarily displays string in the current buffer at position. It has no effect on the undo list or on the buffer's modification status.
The momentary display remains until the next input event. If the next input event is char,
momentary-string-displayignores it and returns. Otherwise, that event remains buffered for subsequent use as input. Thus, typing char will simply remove the string from the display, while typing (say) C-f will remove the string from the display and later (presumably) move point forward. The argument char is a space by default.The return value of
momentary-string-displayis not meaningful.If the string string does not contain control characters, you can do the same job in a more general way by creating (and then subsequently deleting) an overlay with a
before-stringproperty. See Overlay Properties.If message is non-
nil, it is displayed in the echo area while string is displayed in the buffer. If it isnil, a default message says to type char to continue.In this example, point is initially located at the beginning of the second line:
---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") => t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------
You can use overlays to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay.
The visual effect of an overlay is the same as of the corresponding text property (see Text Properties). However, due to a different implementation, overlays generally don't scale well (many operations take a time that is proportional to the number of overlays in the buffer). If you need to affect the visual appearance of many portions in the buffer, we recommend using text properties.
An overlay uses markers to record its beginning and end; thus, editing the text of the buffer adjusts the beginning and end of each overlay so that it stays with the text. When you create the overlay, you can specify whether text inserted at the beginning should be inside the overlay or outside, and likewise for the end of the overlay.
This section describes the functions to create, delete and move overlays, and to examine their contents. Overlay changes are not recorded in the buffer's undo list, since the overlays are not part of the buffer's contents.
This function creates and returns an overlay that belongs to buffer and ranges from start to end. Both start and end must specify buffer positions; they may be integers or markers. If buffer is omitted, the overlay is created in the current buffer.
An overlay whose start and end specify the same buffer position is known as empty. A non-empty overlay can become empty if the text between its start and end is deleted. When that happens, the overlay is by default not deleted, but you can cause it to be deleted by giving it the `evaporate' property (see evaporate property).
The arguments front-advance and rear-advance specify the marker insertion type for the start of the overlay and for the end of the overlay, respectively. See Marker Insertion Types. If they are both
nil, the default, then the overlay extends to include any text inserted at the beginning, but not text inserted at the end. If front-advance is non-nil, text inserted at the beginning of the overlay is excluded from the overlay. If rear-advance is non-nil, text inserted at the end of the overlay is included in the overlay.
This function returns the position at which overlay starts, as an integer.
This function returns the position at which overlay ends, as an integer.
This function returns the buffer that overlay belongs to. It returns
nilif overlay has been deleted.
This function deletes overlay. The overlay continues to exist as a Lisp object, and its property list is unchanged, but it ceases to be attached to the buffer it belonged to, and ceases to have any effect on display.
A deleted overlay is not permanently disconnected. You can give it a position in a buffer again by calling
move-overlay.
This function moves overlay to buffer, and places its bounds at start and end. Both arguments start and end must specify buffer positions; they may be integers or markers.
If buffer is omitted, overlay stays in the same buffer it was already associated with; if overlay was deleted, it goes into the current buffer.
The return value is overlay.
This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be lost.
This function removes all the overlays between start and end whose property name has the value value. It can move the endpoints of the overlays in the region, or split them.
If name is omitted or
nil, it means to delete all overlays in the specified region. If start and/or end are omitted ornil, that means the beginning and end of the buffer respectively. Therefore,(remove-overlays)removes all the overlays in the current buffer.
This function returns a copy of overlay. The copy has the same endpoints and properties as overlay. However, the marker insertion type for the start of the overlay and for the end of the overlay are set to their default values (see Marker Insertion Types).
Here are some examples:
;; Create an overlay. (setq foo (make-overlay 1 10)) => #<overlay from 1 to 10 in display.texi> (overlay-start foo) => 1 (overlay-end foo) => 10 (overlay-buffer foo) => #<buffer display.texi> ;; Give it a property we can check later. (overlay-put foo 'happy t) => t ;; Verify the property is present. (overlay-get foo 'happy) => t ;; Move the overlay. (move-overlay foo 5 20) => #<overlay from 5 to 20 in display.texi> (overlay-start foo) => 5 (overlay-end foo) => 20 ;; Delete the overlay. (delete-overlay foo) => nil ;; Verify it is deleted. foo => #<overlay in no buffer> ;; A deleted overlay has no position. (overlay-start foo) => nil (overlay-end foo) => nil (overlay-buffer foo) => nil ;; Undelete the overlay. (move-overlay foo 1 20) => #<overlay from 1 to 20 in display.texi> ;; Verify the results. (overlay-start foo) => 1 (overlay-end foo) => 20 (overlay-buffer foo) => #<buffer display.texi> ;; Moving and deleting the overlay does not change its properties. (overlay-get foo 'happy) => t
Emacs stores the overlays of each buffer in two lists, divided around an arbitrary center position. One list extends backwards through the buffer from that center position, and the other extends forwards from that center position. The center position can be anywhere in the buffer.
This function recenters the overlays of the current buffer around position pos. That makes overlay lookup faster for positions near pos, but slower for positions far away from pos.
A loop that scans the buffer forwards, creating overlays, can run
faster if you do (overlay-recenter (point-max)) first.
Overlay properties are like text properties in that the properties that alter how a character is displayed can come from either source. But in most respects they are different. See Text Properties, for comparison.
Text properties are considered a part of the text; overlays and their properties are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text property changes, overlay property changes are not recorded in the buffer's undo list.
Since more than one overlay can specify a property value for the same character, Emacs lets you specify a priority value of each overlay. In case two overlays have the same priority value, and one is nested in the other, then the inner one will have priority over the outer one. If neither is nested in the other then you should not make assumptions about which overlay will prevail.
These functions read and set the properties of an overlay:
This function returns the value of property prop recorded in overlay, if any. If overlay does not record any value for that property, but it does have a
categoryproperty which is a symbol, that symbol's prop property is used. Otherwise, the value isnil.
This function sets the value of property prop recorded in overlay to value. It returns value.
See also the function get-char-property which checks both
overlay properties and text properties for a given character.
See Examining Properties.
Many overlay properties have special meanings; here is a table of them:
prioritynil
(or zero), or a positive integer. Any other value has undefined behavior.
The priority matters when two or more overlays cover the same
character and both specify the same property; the one whose
priority value is larger overrides the other. For the
face property, the higher priority overlay's value does not
completely override the other value; instead, its face attributes
override the face attributes of the lower priority face
property.
Currently, all overlays take priority over text properties.
Note that Emacs sometimes uses non-numeric priority values for some of
its internal overlays, so do not try to do arithmetic on the
priority of an overlay (unless it is one that you created). If you
need to put overlays in priority order, use the sorted argument
of overlays-at. See Finding Overlays.
windowwindow property is non-nil, then the overlay
applies only on that window.
categorycategory property, we call it the
category of the overlay. It should be a symbol. The properties
of the symbol serve as defaults for the properties of the overlay.
face(keyword
value ...), where each keyword is a face attribute
name and value is a value for that attribute.
(foreground-color . color-name)
or (background-color . color-name). This specifies the
foreground or background color, similar to (:foreground
color-name) or (:background color-name). This
form is supported for backward compatibility only, and should be
avoided.
mouse-faceface when the mouse is within
the range of the overlay. However, Emacs ignores all face attributes
from this property that alter the text size (e.g., :height,
:weight, and :slant). Those attributes are always the
same as in the unhighlighted text.
displayhelp-echohelp-echo property, then when you move the
mouse onto the text in the overlay, Emacs displays a help string in the
echo area, or in the tooltip window. For details see Text help-echo.
fieldfield property constitute a
field. Some motion functions including forward-word and
beginning-of-line stop moving at a field boundary.
See Fields.
modification-hooksThe hook functions are called both before and after each change. If the functions save the information they receive, and compare notes between calls, they can determine exactly what change has been made in the buffer text.
When called before a change, each function receives four arguments: the
overlay, nil, and the beginning and end of the text range to be
modified.
When called after a change, each function receives five arguments: the
overlay, t, the beginning and end of the text range just
modified, and the length of the pre-change text replaced by that range.
(For an insertion, the pre-change length is zero; for a deletion, that
length is the number of characters deleted, and the post-change
beginning and end are equal.)
If these functions modify the buffer, they should bind
inhibit-modification-hooks to t around doing so, to
avoid confusing the internal mechanism that calls these hooks.
Text properties also support the modification-hooks property,
but the details are somewhat different (see Special Properties).
insert-in-front-hooksmodification-hooks functions.
insert-behind-hooksmodification-hooks functions.
invisibleinvisible property can make the text in the overlay
invisible, which means that it does not appear on the screen.
See Invisible Text, for details.
intangibleintangible property on an overlay works just like the
intangible text property. It is obsolete. See Special Properties, for details.
isearch-open-invisibleisearch-open-invisible-temporarybefore-stringafter-stringline-prefixwrap-prefixevaporatenil, the overlay is deleted automatically
if it becomes empty (i.e., if its length becomes zero). If you give
an empty overlay (see empty overlay) a
non-nil evaporate property, that deletes it immediately.
Note that, unless an overlay has this property, it will not be deleted
when the text between its starting and ending positions is deleted
from the buffer.
keymapnil, it specifies a keymap for a portion of the
text. This keymap is used when the character after point is within the
overlay, and takes precedence over most other keymaps. See Active Keymaps.
local-maplocal-map property is similar to keymap but replaces the
buffer's local map rather than augmenting existing keymaps. This also means it
has lower precedence than minor mode keymaps.
The keymap and local-map properties do not affect a
string displayed by the before-string, after-string, or
display properties. This is only relevant for mouse clicks and
other mouse events that fall on the string, since point is never on
the string. To bind special mouse events for the string, assign it a
keymap or local-map text property. See Special Properties.
This function returns a list of all the overlays that cover the character at position pos in the current buffer. If sorted is non-
nil, the list is in decreasing order of priority, otherwise it is in no particular order. An overlay contains position pos if it begins at or before pos, and ends after pos.To illustrate usage, here is a Lisp function that returns a list of the overlays that specify property prop for the character at point:
(defun find-overlays-specifying (prop) (let ((overlays (overlays-at (point))) found) (while overlays (let ((overlay (car overlays))) (if (overlay-get overlay prop) (setq found (cons overlay found)))) (setq overlays (cdr overlays))) found))
This function returns a list of the overlays that overlap the region beg through end. An overlay overlaps with a region if it contains one or more characters in the region; empty overlays (see empty overlay) overlap if they are at beg, strictly between beg and end, or at end when end denotes the position at the end of the buffer.
This function returns the buffer position of the next beginning or end of an overlay, after pos. If there is none, it returns
(point-max).
This function returns the buffer position of the previous beginning or end of an overlay, before pos. If there is none, it returns
(point-min).
As an example, here's a simplified (and inefficient) version of the
primitive function next-single-char-property-change
(see Property Search). It searches forward from position
pos for the next position where the value of a given property
prop, as obtained from either overlays or text properties,
changes.
(defun next-single-char-property-change (position prop)
(save-excursion
(goto-char position)
(let ((propval (get-char-property (point) prop)))
(while (and (not (eobp))
(eq (get-char-property (point) prop) propval))
(goto-char (min (next-overlay-change (point))
(next-single-property-change (point) prop)))))
(point)))
Since not all characters have the same width, these functions let you check the width of a character. See Primitive Indent, and Screen Lines, for related functions.
This function returns the width in columns of the character char, if it were displayed in the current buffer (i.e., taking into account the buffer's display table, if any; see Display Tables). The width of a tab character is usually
tab-width(see Usual Display).
This function returns the width in columns of the string string, if it were displayed in the current buffer and the selected window.
This function returns the part of string that fits within width columns, as a new string.
If string does not reach width, then the result ends where string ends. If one multi-column character in string extends across the column width, that character is not included in the result. Thus, the result can fall short of width but cannot go beyond it.
The optional argument start-column specifies the starting column. If this is non-
nil, then the first start-column columns of the string are omitted from the value. If one multi-column character in string extends across the column start-column, that character is not included.The optional argument padding, if non-
nil, is a padding character added at the beginning and end of the result string, to extend it to exactly width columns. The padding character is used at the end of the result if it falls short of width. It is also used at the beginning of the result if one multi-column character in string extends across the column start-column.If ellipsis is non-
nil, it should be a string which will replace the end of string (including any padding) if it extends beyond width, unless the display width of string is equal to or less than the display width of ellipsis. If ellipsis is non-niland not a string, it stands for the value of the variabletruncate-string-ellipsis.(truncate-string-to-width "\tab\t" 12 4) => "ab" (truncate-string-to-width "\tab\t" 12 4 ?\s) => " ab "
The following function returns the size in pixels of text as if it were
displayed in a given window. This function is used by
fit-window-to-buffer and fit-frame-to-buffer
(see Resizing Windows) to make a window exactly as large as the text
it contains.
This function returns the size of the text of window's buffer in pixels. window must be a live window and defaults to the selected one. The return value is a cons of the maximum pixel-width of any text line and the maximum pixel-height of all text lines.
The optional argument from, if non-
nil, specifies the first text position to consider and defaults to the minimum accessible position of the buffer. If from ist, it uses the minimum accessible position that is not a newline character. The optional argument to, if non-nil, specifies the last text position to consider and defaults to the maximum accessible position of the buffer. If to ist, it uses the maximum accessible position that is not a newline character.The optional argument x-limit, if non-
nil, specifies the maximum pixel-width that can be returned. x-limitnilor omitted, means to use the pixel-width of window's body (see Window Sizes); this is useful when the caller does not intend to change the width of window. Otherwise, the caller should specify here the maximum width window's body may assume. Text whose x-coordinate is beyond x-limit is ignored. Since calculating the width of long lines can take some time, it's always a good idea to make this argument as small as needed; in particular, if the buffer might contain long lines that will be truncated anyway.The optional argument y-limit, if non-
nil, specifies the maximum pixel-height that can be returned. Text lines whose y-coordinate is beyond y-limit are ignored. Since calculating the pixel-height of a large buffer can take some time, it makes sense to specify this argument; in particular, if the caller does not know the size of the buffer.The optional argument mode-and-header-line
nilor omitted means to not include the height of the mode- or header-line of window in the return value. If it is either the symbolmode-lineorheader-line, include only the height of that line, if present, in the return value. If it ist, include the height of both, if present, in the return value.
The total height of each display line consists of the height of the contents of the line, plus optional additional vertical line spacing above or below the display line.
The height of the line contents is the maximum height of any character or image on that display line, including the final newline if there is one. (A display line that is continued doesn't include a final newline.) That is the default line height, if you do nothing to specify a greater height. (In the most common case, this equals the height of the corresponding frame's default font, see Frame Font.)
There are several ways to explicitly specify a larger line height, either by specifying an absolute height for the display line, or by specifying vertical space. However, no matter what you specify, the actual line height can never be less than the default.
A newline can have a line-height text or overlay property
that controls the total height of the display line ending in that
newline.
If the property value is t, the newline character has no
effect on the displayed height of the line—the visible contents
alone determine the height. This is useful for tiling small images
(or image slices) without adding blank areas between the images.
If the property value is a list of the form (height
total), that adds extra space below the display line.
First Emacs uses height as a height spec to control extra space
above the line; then it adds enough space below the line
to bring the total line height up to total. In this case, the
other ways to specify the line spacing are ignored.
Any other kind of property value is a height spec, which translates into a number—the specified line height. There are several ways to write a height spec; here's how each of them translates into a number:
(face . ratio)
nil which means a ratio of 1.
If face is t, it refers to the current face.
(nil . ratio)
Thus, any valid height spec determines the height in pixels, one way or another. If the line contents' height is less than that, Emacs adds extra vertical space above the line to achieve the specified total height.
If you don't specify the line-height property, the line's
height consists of the contents' height plus the line spacing.
There are several ways to specify the line spacing for different
parts of Emacs text.
On graphical terminals, you can specify the line spacing for all
lines in a frame, using the line-spacing frame parameter
(see Layout Parameters). However, if the default value of
line-spacing is non-nil, it overrides the
frame's line-spacing parameter. An integer specifies the
number of pixels put below lines. A floating-point number specifies
the spacing relative to the frame's default line height.
You can specify the line spacing for all lines in a buffer via the
buffer-local line-spacing variable. An integer specifies
the number of pixels put below lines. A floating-point number
specifies the spacing relative to the default frame line height. This
overrides line spacings specified for the frame.
Finally, a newline can have a line-spacing text or overlay
property that overrides the default frame line spacing and the buffer
local line-spacing variable, for the display line ending in
that newline.
One way or another, these mechanisms specify a Lisp value for the spacing of each line. The value is a height spec, and it translates into a Lisp value as described above. However, in this case the numeric height value specifies the line spacing, rather than the line height.
On text terminals, the line spacing cannot be altered.
A face is a collection of graphical attributes for displaying text: font, foreground color, background color, optional underlining, etc. Faces control how Emacs displays text in buffers, as well as other parts of the frame such as the mode line.
One way to represent a face is as a property list of attributes,
like (:foreground "red" :weight bold). Such a list is called
an anonymous face. For example, you can assign an anonymous
face as the value of the face text property, and Emacs will
display the underlying text with the specified attributes.
See Special Properties.
More commonly, a face is referred to via a face name: a Lisp
symbol associated with a set of face attributes19. Named faces are
defined using the defface macro (see Defining Faces).
Emacs comes with several standard named faces (see Basic Faces).
Many parts of Emacs required named faces, and do not accept
anonymous faces. These include the functions documented in
Attribute Functions, and the variable font-lock-keywords
(see Search-based Fontification). Unless otherwise stated, we
will use the term face to refer only to named faces.
This function returns a non-
nilvalue if object is a named face: a Lisp symbol or string which serves as a face name. Otherwise, it returnsnil.
Face attributes determine the visual appearance of a face. The following table lists all the face attributes, their possible values, and their effects.
Apart from the values given below, each face attribute can have the
value unspecified. This special value means that the face
doesn't specify that attribute directly. An unspecified
attribute tells Emacs to refer instead to a parent face (see the
description :inherit attribute below); or, failing that, to an
underlying face (see Displaying Faces). The default face
must specify all attributes.
Some of these attributes are meaningful only on certain kinds of displays. If your display cannot handle a certain attribute, the attribute is ignored.
:familyfont-family-list (see below) returns a list of available family
names. See Fontsets, for information about fontsets.
:foundry:family attribute (a string). See Fonts.
:widthultra-condensed, extra-condensed, condensed,
semi-condensed, normal, semi-expanded,
expanded, extra-expanded, or ultra-expanded.
:heightThe value can also be floating point or a function, which specifies the height relative to an underlying face (see Displaying Faces). A floating-point value specifies the amount by which to scale the height of the underlying face. A function value is called with one argument, the height of the underlying face, and returns the height of the new face. If the function is passed an integer argument, it must return an integer.
The height of the default face must be specified using an integer;
floating point and function values are not allowed.
:weightultra-bold, extra-bold, bold, semi-bold,
normal, semi-light, light, extra-light, or
ultra-light. On text terminals which support
variable-brightness text, any weight greater than normal is displayed
as extra bright, and any weight less than normal is displayed as
half-bright.
:slantitalic, oblique,
normal, reverse-italic, or reverse-oblique. On
text terminals that support variable-brightness text, slanted text is
displayed as half-bright.
:foreground:distant-foreground:foreground
but the color is only used as a foreground when the background color is
near to the foreground that would have been used. This is useful for
example when marking text (i.e., the region face). If the text has a foreground
that is visible with the region face, that foreground is used.
If the foreground is near the region face background,
:distant-foreground is used instead so the text is readable.
:background:underline:underline attribute are:
nilt(:color color :style style)
foreground-color,
meaning the foreground color of the face. Omitting the attribute
:color means to use the foreground color of the face.
style should be a symbol line or wave, meaning to
use a straight or wavy line. Omitting the attribute :style
means to use a straight line.
:overlinet, overlining uses the foreground color of the
face. If the value is a string, overlining uses that color. The
value nil means do not overline.
:strike-through:overline.
:box:box attribute, and what they mean:
nilt(:line-width width :color color :style style)
The value color specifies the color to draw with. The default is the foreground color of the face for simple boxes, and the background color of the face for 3D boxes.
The value style specifies whether to draw a 3D box. If it is
released-button, the box looks like a 3D button that is not being
pressed. If it is pressed-button, the box looks like a 3D button
that is being pressed. If it is nil or omitted, a plain 2D box
is used.
:inverse-videot (yes) or nil (no).
:stippleThe value can be a string; that should be the name of a file containing
external-format X bitmap data. The file is found in the directories
listed in the variable x-bitmap-file-path.
Alternatively, the value can specify the bitmap directly, with a list
of the form (width height data). Here,
width and height specify the size in pixels, and
data is a string containing the raw bits of the bitmap, row by
row. Each row occupies (width + 7) / 8 consecutive bytes
in the string (which should be a unibyte string for best results).
This means that each row always occupies at least one whole byte.
If the value is nil, that means use no stipple pattern.
Normally you do not need to set the stipple attribute, because it is
used automatically to handle certain shades of gray.
:fontWhen specifying this attribute using set-face-attribute
(see Attribute Functions), you may also supply a font spec, a font
entity, or a string. Emacs converts such values to an appropriate
font object, and stores that font object as the actual attribute
value. If you specify a string, the contents of the string should be
a font name (see Fonts); if the
font name is an XLFD containing wildcards, Emacs chooses the first
font matching those wildcards. Specifying this attribute also changes
the values of the :family, :foundry, :width,
:height, :weight, and :slant attributes.
:inheritThis function returns a list of available font family names. The optional argument frame specifies the frame on which the text is to be displayed; if it is
nil, the selected frame is used.
This variable specifies the minimum distance between the baseline and the underline, in pixels, when displaying underlined text.
This variable specifies a list of directories for searching for bitmap files, for the
:stippleattribute.
This returns
tif object is a valid bitmap specification, suitable for use with:stipple(see above). It returnsnilotherwise.
The usual way to define a face is through the defface macro.
This macro associates a face name (a symbol) with a default face
spec. A face spec is a construct which specifies what attributes a
face should have on any given terminal; for example, a face spec might
specify one foreground color on high-color terminals, and a different
foreground color on low-color terminals.
People are sometimes tempted to create a variable whose value is a
face name. In the vast majority of cases, this is not necessary; the
usual procedure is to define a face with defface, and then use
its name directly.
This macro declares face as a named face whose default face spec is given by spec. You should not quote the symbol face, and it should not end in `-face' (that would be redundant). The argument doc is a documentation string for the face. The additional keyword arguments have the same meanings as in
defgroupanddefcustom(see Common Keywords).If face already has a default face spec, this macro does nothing.
The default face spec determines face's appearance when no customizations are in effect (see Customization). If face has already been customized (via Custom themes or via customizations read from the init file), its appearance is determined by the custom face spec(s), which override the default face spec spec. However, if the customizations are subsequently removed, the appearance of face will again be determined by its default face spec.
As an exception, if you evaluate a
deffaceform with C-M-x in Emacs Lisp mode (eval-defun), a special feature ofeval-defunoverrides any custom face specs on the face, causing the face to reflect exactly what thedeffacesays.The spec argument is a face spec, which states how the face should appear on different kinds of terminals. It should be an alist whose elements each have the form
(display . plist)display specifies a class of terminals (see below). plist is a property list of face attributes and their values, specifying how the face appears on such terminals. For backward compatibility, you can also write an element as
(display plist).The display part of an element of spec determines which terminals the element matches. If more than one element of spec matches a given terminal, the first element that matches is the one used for that terminal. There are three possibilities for display:
default- This element of spec doesn't match any terminal; instead, it specifies defaults that apply to all terminals. This element, if used, must be the first element of spec. Each of the following elements can override any or all of these defaults.
t- This element of spec matches all terminals. Therefore, any subsequent elements of spec are never used. Normally
tis used in the last (or only) element of spec.
- a list
- If display is a list, each element should have the form
(characteristic value...). Here characteristic specifies a way of classifying terminals, and the values are possible classifications which display should apply to. Here are the possible values of characteristic:
type- The kind of window system the terminal uses—either
graphic(any graphics-capable display),x,pc(for the MS-DOS console),w32(for MS Windows 9X/NT/2K/XP), ortty(a non-graphics-capable display). See window-system.
class- What kinds of colors the terminal supports—either
color,grayscale, ormono.
background- The kind of background—either
lightordark.
min-colors- An integer that represents the minimum number of colors the terminal should support. This matches a terminal if its
display-color-cellsvalue is at least the specified integer.
supports- Whether or not the terminal can display the face attributes given in value... (see Face Attributes). See Display Face Attribute Testing, for more information on exactly how this testing is done.
If an element of display specifies more than one value for a given characteristic, any of those values is acceptable. If display has more than one element, each element should specify a different characteristic; then each characteristic of the terminal must match one of the values specified for it in display.
For example, here's the definition of the standard face
highlight:
(defface highlight
'((((class color) (min-colors 88) (background light))
:background "darkseagreen2")
(((class color) (min-colors 88) (background dark))
:background "darkolivegreen")
(((class color) (min-colors 16) (background light))
:background "darkseagreen2")
(((class color) (min-colors 16) (background dark))
:background "darkolivegreen")
(((class color) (min-colors 8))
:background "green" :foreground "black")
(t :inverse-video t))
"Basic face for highlighting."
:group 'basic-faces)
Internally, Emacs stores each face's default spec in its
face-defface-spec symbol property (see Symbol Properties).
The saved-face property stores any face spec saved by the user
using the customization buffer; the customized-face property
stores the face spec customized for the current session, but not
saved; and the theme-face property stores an alist associating
the active customization settings and Custom themes with the face
specs for that face. The face's documentation string is stored in the
face-documentation property.
Normally, a face is declared just once, using defface, and
any further changes to its appearance are applied using the Customize
framework (e.g., via the Customize user interface or via the
custom-set-faces function; see Applying Customizations), or
by face remapping (see Face Remapping). In the rare event that
you need to change a face spec directly from Lisp, you can use the
face-spec-set function.
This function applies spec as a face spec for
face. spec should be a face spec, as described in the above documentation fordefface.This function also defines face as a valid face name if it is not already one, and (re)calculates its attributes on existing frames.
The argument spec-type determines which spec to set. If it is
nilorface-override-spec, this function sets the override spec, which overrides over all other face specs on face. If it iscustomized-faceorsaved-face, this function sets the customized spec or the saved custom spec. If it isface-defface-spec, this function sets the default face spec (the same one set bydefface). If it isreset, this function clears out all customization specs and override specs from face (in this case, the value of spec is ignored). Any other value of spec-type is reserved for internal use.
This section describes functions for directly accessing and modifying the attributes of a named face.
This function returns the value of the attribute attribute for face on frame.
If frame is
nil, that means the selected frame (see Input Focus). If frame ist, this function returns the value of the specified attribute for newly-created frames (this is normallyunspecified, unless you have specified some value usingset-face-attribute; see below).If inherit is
nil, only attributes directly defined by face are considered, so the return value may beunspecified, or a relative value. If inherit is non-nil, face's definition of attribute is merged with the faces specified by its:inheritattribute; however the return value may still beunspecifiedor relative. If inherit is a face or a list of faces, then the result is further merged with that face (or faces), until it becomes specified and absolute.To ensure that the return value is always specified and absolute, use a value of
defaultfor inherit; this will resolve any unspecified or relative values by merging with thedefaultface (which is always completely specified).For example,
(face-attribute 'bold :weight) => bold
This function returns non-
nilif value, when used as the value of the face attribute attribute, is relative. This means it would modify, rather than completely override, any value that comes from a subsequent face in the face list or that is inherited from another face.
unspecifiedis a relative value for all attributes. For:height, floating point and function values are also relative.For example:
(face-attribute-relative-p :height 2.0) => t
This function returns an alist of attributes of face. The elements of the result are name-value pairs of the form
(attr-name.attr-value). Optional argument frame specifies the frame whose definition of face to return; if omitted ornil, the returned value describes the default attributes of face for newly created frames.
If value1 is a relative value for the face attribute attribute, returns it merged with the underlying value value2; otherwise, if value1 is an absolute value for the face attribute attribute, returns value1 unchanged.
Normally, Emacs uses the face specs of each face to automatically
calculate its attributes on each frame (see Defining Faces). The
function set-face-attribute can override this calculation by
directly assigning attributes to a face, either on a specific frame or
for all frames. This function is mostly intended for internal usage.
This function sets one or more attributes of face for frame. The attributes specifies in this way override the face spec(s) belonging to face.
The extra arguments arguments specify the attributes to set, and the values for them. They should consist of alternating attribute names (such as
:familyor:underline) and values. Thus,(set-face-attribute 'foo nil :weight 'bold :slant 'italic)sets the attribute
:weighttoboldand the attribute:slanttoitalic.If frame is
t, this function sets the default attributes for newly created frames. If frame isnil, this function sets the attributes for all existing frames, as well as for newly created frames.
The following commands and functions mostly provide compatibility
with old versions of Emacs. They work by calling
set-face-attribute. Values of t and nil for
their frame argument are handled just like
set-face-attribute and face-attribute. The commands
read their arguments using the minibuffer, if called interactively.
These set the
:foregroundattribute (or:backgroundattribute, respectively) of face to color.
This sets the
:stippleattribute of face to pattern.
This sets the
:weightattribute of face to normal if bold-p isnil, and to bold otherwise.
This sets the
:slantattribute of face to normal if italic-p isnil, and to italic otherwise.
This sets the
:underlineattribute of face to underline.
This sets the
:inverse-videoattribute of face to inverse-video-p.
This swaps the foreground and background colors of face face.
The following functions examine the attributes of a face. They
mostly provide compatibility with old versions of Emacs. If you don't
specify frame, they refer to the selected frame; t refers
to the default data for new frames. They return unspecified if
the face doesn't define any value for that attribute. If
inherit is nil, only an attribute directly defined by the
face is returned. If inherit is non-nil, any faces
specified by its :inherit attribute are considered as well, and
if inherit is a face or a list of faces, then they are also
considered, until a specified attribute is found. To ensure that the
return value is always specified, use a value of default for
inherit.
This function returns the name of the font of face face.
If the optional argument frame is specified, it returns the name of the font of face for that frame. If frame is omitted or
nil, the selected frame is used. And, in this case, if the optional third argument character is supplied, it returns the font name used for character.
These functions return the foreground color (or background color, respectively) of face face, as a string.
This function returns the name of the background stipple pattern of face face, or
nilif it doesn't have one.
This function returns a non-
nilvalue if the:weightattribute of face is bolder than normal (i.e., one ofsemi-bold,bold,extra-bold, orultra-bold). Otherwise, it returnsnil.
This function returns a non-
nilvalue if the:slantattribute of face isitalicoroblique, andnilotherwise.
This function returns non-
nilif face face specifies a non-nil:underlineattribute.
This function returns non-
nilif face face specifies a non-nil:inverse-videoattribute.
When Emacs displays a given piece of text, the visual appearance of the text may be determined by faces drawn from different sources. If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces. Here is the order in which Emacs merges the faces, from highest to lowest priority:
region face. See Standard Faces.
nil face
property, Emacs applies the face(s) specified by that property. If
the overlay has a mouse-face property and the mouse is near
enough to the overlay, Emacs applies the face or face attributes
specified by the mouse-face property instead. See Overlay Properties.
When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. See Overlays.
face or mouse-face property,
Emacs applies the specified faces and face attributes. See Special Properties. (This is how Font Lock mode faces are applied.
See Font Lock Mode.)
mode-line face. For the mode line of a
non-selected window, Emacs applies the mode-line-inactive face.
For a header line, Emacs applies the header-line face.
default face.
At each stage, if a face has a valid :inherit attribute,
Emacs treats any attribute with an unspecified value as having
the corresponding value drawn from the parent face(s). see Face Attributes. Note that the parent face(s) may also leave the
attribute unspecified; in that case, the attribute remains unspecified
at the next level of face merging.
The variable face-remapping-alist is used for buffer-local or
global changes in the appearance of a face. For instance, it is used
to implement the text-scale-adjust command (see Text Scale).
The value of this variable is an alist whose elements have the form
(face.remapping). This causes Emacs to display any text having the face face with remapping, rather than the ordinary definition of face.remapping may be any face spec suitable for a
facetext property: either a face (i.e., a face name or a property list of attribute/value pairs), or a list of faces. For details, see the description of thefacetext property in Special Properties. remapping serves as the complete specification for the remapped face—it replaces the normal definition of face, instead of modifying it.If
face-remapping-alistis buffer-local, its local value takes effect only within that buffer.Note: face remapping is non-recursive. If remapping references the same face name face, either directly or via the
:inheritattribute of some other face in remapping, that reference uses the normal definition of face. For instance, if themode-lineface is remapped using this entry inface-remapping-alist:(mode-line italic mode-line)then the new definition of the
mode-lineface inherits from theitalicface, and the normal (non-remapped) definition ofmode-lineface.
The following functions implement a higher-level interface to
face-remapping-alist. Most Lisp code should use these
functions instead of setting face-remapping-alist directly, to
avoid trampling on remappings applied elsewhere. These functions are
intended for buffer-local remappings, so they all make
face-remapping-alist buffer-local as a side-effect. They manage
face-remapping-alist entries of the form
(face relative-spec-1 relative-spec-2 ... base-spec)
where, as explained above, each of the relative-spec-N and
base-spec is either a face name, or a property list of
attribute/value pairs. Each of the relative remapping entries,
relative-spec-N, is managed by the
face-remap-add-relative and face-remap-remove-relative
functions; these are intended for simple modifications like changing
the text size. The base remapping entry, base-spec, has
the lowest priority and is managed by the face-remap-set-base
and face-remap-reset-base functions; it is intended for major
modes to remap faces in the buffers they control.
This function adds the face spec in specs as relative remappings for face face in the current buffer. The remaining arguments, specs, should form either a list of face names, or a property list of attribute/value pairs.
The return value is a Lisp object that serves as a cookie; you can pass this object as an argument to
face-remap-remove-relativeif you need to remove the remapping later.;; Remap the 'escape-glyph' face into a combination ;; of the 'highlight' and 'italic' faces: (face-remap-add-relative 'escape-glyph 'highlight 'italic) ;; Increase the size of the 'default' face by 50%: (face-remap-add-relative 'default :height 1.5)
This function removes a relative remapping previously added by
face-remap-add-relative. cookie should be the Lisp object returned byface-remap-add-relativewhen the remapping was added.
This function sets the base remapping of face in the current buffer to specs. If specs is empty, the default base remapping is restored, similar to calling
face-remap-reset-base(see below); note that this is different from specs containing a single valuenil, which has the opposite result (the global definition of face is ignored).This overwrites the default base-spec, which inherits the global face definition, so it is up to the caller to add such inheritance if so desired.
This function sets the base remapping of face to its default value, which inherits from face's global definition.
Here are additional functions for creating and working with faces.
This function returns the face number of face face. This is a number that uniquely identifies a face at low levels within Emacs. It is seldom necessary to refer to a face by its face number.
This function returns the documentation string of face face, or
nilif none was specified for it.
This returns
tif the faces face1 and face2 have the same attributes for display.
This returns non-
nilif the face face displays differently from the default face.
A face alias provides an equivalent name for a face. You can
define a face alias by giving the alias symbol the face-alias
property, with a value of the target face name. The following example
makes modeline an alias for the mode-line face.
(put 'modeline 'face-alias 'mode-line)
This macro defines
obsolete-faceas an alias for current-face, and also marks it as obsolete, indicating that it may be removed in future. when should be a string indicating whenobsolete-facewas made obsolete (usually a version number string).
This hook is used for automatically assigning faces to text in the buffer. It is part of the implementation of Jit-Lock mode, used by Font-Lock.
This variable holds a list of functions that are called by Emacs redisplay as needed, just before doing redisplay. They are called even when Font Lock Mode isn't enabled. When Font Lock Mode is enabled, this variable usually holds just one function,
jit-lock-function.The functions are called in the order listed, with one argument, a buffer position pos. Collectively they should attempt to assign faces to the text in the current buffer starting at pos.
The functions should record the faces they assign by setting the
faceproperty. They should also add a non-nilfontifiedproperty to all the text they have assigned faces to. That property tells redisplay that faces have been assigned to that text already.It is probably a good idea for the functions to do nothing if the character after pos already has a non-
nilfontifiedproperty, but this is not required. If one function overrides the assignments made by a previous one, the properties after the last function finishes are the ones that really matter.For efficiency, we recommend writing these functions so that they usually assign faces to around 400 to 600 characters at each call.
If your Emacs Lisp program needs to assign some faces to text, it is often a good idea to use certain existing faces or inherit from them, rather than defining entirely new faces. This way, if other users have customized the basic faces to give Emacs a certain look, your program will fit in without additional customization.
Some of the basic faces defined in Emacs are listed below. In addition to these, you might want to make use of the Font Lock faces for syntactic highlighting, if highlighting is not already handled by Font Lock mode, or if some Font Lock faces are not in use. See Faces for Font Lock.
defaultbolditalicbold-italicunderlinefixed-pitchvariable-pitchbold
has a bold :weight attribute), with all other attributes
unspecified (and so given by default).
shadowlinklink-visitedhighlightmouse-face property for cursor
highlighting (see Special Properties).
matchisearchlazy-highlighterrorwarningsuccess
Before Emacs can draw a character on a graphical display, it must
select a font for that character20. See Fonts. Normally,
Emacs automatically chooses a font based on the faces assigned to that
character—specifically, the face attributes :family,
:weight, :slant, and :width (see Face Attributes). The choice of font also depends on the character to be
displayed; some fonts can only display a limited set of characters.
If no available font exactly fits the requirements, Emacs looks for
the closest matching font. The variables in this section
control how Emacs makes this selection.
If a given family is specified but does not exist, this variable specifies alternative font families to try. Each element should have this form:
(family alternate-families...)If family is specified but not available, Emacs will try the other families given in alternate-families, one by one, until it finds a family that does exist.
If there is no font that exactly matches all desired face attributes (
:width,:height,:weight, and:slant), this variable specifies the order in which these attributes should be considered when selecting the closest matching font. The value should be a list containing those four attribute symbols, in order of decreasing importance. The default is(:width :height :weight :slant).Font selection first finds the best available matches for the first attribute in the list; then, among the fonts which are best in that way, it searches for the best matches in the second attribute, and so on.
The attributes
:weightand:widthhave symbolic values in a range centered aroundnormal. Matches that are more extreme (farther fromnormal) are somewhat preferred to matches that are less extreme (closer tonormal); this is designed to ensure that non-normal faces contrast with normal ones, whenever possible.One example of a case where this variable makes a difference is when the default font has no italic equivalent. With the default ordering, the
italicface will use a non-italic font that is similar to the default one. But if you put:slantbefore:height, theitalicface will use an italic font, even if its height is not quite right.
This variable lets you specify alternative font registries to try, if a given registry is specified and doesn't exist. Each element should have this form:
(registry alternate-registries...)If registry is specified but not available, Emacs will try the other registries given in alternate-registries, one by one, until it finds a registry that does exist.
Emacs can make use of scalable fonts, but by default it does not use them.
This variable controls which scalable fonts to use. A value of
nil, the default, means do not use scalable fonts.tmeans to use any scalable font that seems appropriate for the text.Otherwise, the value must be a list of regular expressions. Then a scalable font is enabled for use if its name matches any regular expression in the list. For example,
(setq scalable-fonts-allowed '("iso10646-1$"))allows the use of scalable fonts with registry
iso10646-1.
This variable specifies scaling for certain faces. Its value should be a list of elements of the form
(fontname-regexp . scale-factor)If fontname-regexp matches the font name that is about to be used, this says to choose a larger similar font according to the factor scale-factor. You would use this feature to normalize the font size if certain fonts are bigger or smaller than their nominal heights and widths would suggest.
This function returns a list of available font names that match name. name should be a string containing a font name in either the Fontconfig, GTK, or XLFD format (see Fonts). Within an XLFD string, wildcard characters may be used: the `*' character matches any substring, and the `?' character matches any single character. Case is ignored when matching font names.
If the optional arguments reference-face and frame are specified, the returned list includes only fonts that are the same size as reference-face (a face name) currently is on the frame frame.
The optional argument maximum sets a limit on how many fonts to return. If it is non-
nil, then the return value is truncated after the first maximum matching fonts. Specifying a small value for maximum can make this function much faster, in cases where many fonts match the pattern.The optional argument width specifies a desired font width. If it is non-
nil, the function only returns those fonts whose characters are (on average) width times as wide as reference-face.
This function returns a list describing the available fonts for family family on frame. If family is omitted or
nil, this list applies to all families, and therefore, it contains all available fonts. Otherwise, family must be a string; it may contain the wildcards `?' and `*'.The list describes the display that frame is on; if frame is omitted or
nil, it applies to the selected frame's display (see Input Focus).Each element in the list is a vector of the following form:
[family width point-size weight slant fixed-p full registry-and-encoding]The first five elements correspond to face attributes; if you specify these attributes for a face, it will use this font.
The last three elements give additional information about the font. fixed-p is non-
nilif the font is fixed-pitch. full is the full name of the font, and registry-and-encoding is a string giving the registry and encoding of the font.
A fontset is a list of fonts, each assigned to a range of character codes. An individual font cannot display the whole range of characters that Emacs supports, but a fontset can. Fontsets have names, just as fonts do, and you can use a fontset name in place of a font name when you specify the font for a frame or a face. Here is information about defining a fontset under Lisp program control.
This function defines a new fontset according to the specification string fontset-spec. The string should have this format:
fontpattern, [charset:font]...Whitespace characters before and after the commas are ignored.
The first part of the string, fontpattern, should have the form of a standard X font name, except that the last two fields should be `fontset-alias'.
The new fontset has two names, one long and one short. The long name is fontpattern in its entirety. The short name is `fontset-alias'. You can refer to the fontset by either name. If a fontset with the same name already exists, an error is signaled, unless noerror is non-
nil, in which case this function does nothing.If optional argument style-variant-p is non-
nil, that says to create bold, italic and bold-italic variants of the fontset as well. These variant fontsets do not have a short name, only a long one, which is made by altering fontpattern to indicate the bold and/or italic status.The specification string also says which fonts to use in the fontset. See below for the details.
The construct `charset:font' specifies which font to use (in this fontset) for one particular character set. Here, charset is the name of a character set, and font is the font to use for that character set. You can use this construct any number of times in the specification string.
For the remaining character sets, those that you don't specify explicitly, Emacs chooses a font based on fontpattern: it replaces `fontset-alias' with a value that names one character set. For the ASCII character set, `fontset-alias' is replaced with `ISO8859-1'.
In addition, when several consecutive fields are wildcards, Emacs collapses them into a single wildcard. This is to prevent use of auto-scaled fonts. Fonts made by scaling larger fonts are not usable for editing, and scaling a smaller font is not useful because it is better to use the smaller font in its own size, which Emacs does.
Thus if fontpattern is this,
-*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24
the font specification for ASCII characters would be this:
-*-fixed-medium-r-normal-*-24-*-ISO8859-1
and the font specification for Chinese GB2312 characters would be this:
-*-fixed-medium-r-normal-*-24-*-gb2312*-*
You may not have any Chinese font matching the above font specification. Most X distributions include only Chinese fonts that have `song ti' or `fangsong ti' in the family field. In such a case, `Fontset-n' can be specified as below:
Emacs.Fontset-0: -*-fixed-medium-r-normal-*-24-*-*-*-*-*-fontset-24,\
chinese-gb2312:-*-*-medium-r-normal-*-24-*-gb2312*-*
Then, the font specifications for all but Chinese GB2312 characters have `fixed' in the family field, and the font specification for Chinese GB2312 characters has a wild card `*' in the family field.
This function modifies the existing fontset name to use the font matching with font-spec for the specified character.
If name is
nil, this function modifies the fontset of the selected frame or that of frame if frame is notnil.If name is
t, this function modifies the default fontset, whose short name is `fontset-default'.In addition to specifying a single codepoint, character may be a cons
(from.to), where from and to are character codepoints. In that case, use font-spec for all the characters in the range from and to (inclusive).character may be a charset. In that case, use font-spec for all character in the charsets.
character may be a script name. In that case, use font-spec for all character in the charsets.
font-spec may be a font-spec object created by the function
font-spec(see Low-Level Font).font-spec may be a cons;
(family.registry), where family is a family name of a font (possibly including a foundry name at the head), registry is a registry name of a font (possibly including an encoding name at the tail).font-spec may be a font name string.
font-spec may be
nil, which explicitly specifies that there's no font for the specified character. This is useful, for example, to avoid expensive system-wide search for fonts for characters that have no glyphs, like those from the Unicode Private Use Area (PUA).The optional argument add, if non-
nil, specifies how to add font-spec to the font specifications previously set. If it isprepend, font-spec is prepended. If it isappend, font-spec is appended. By default, font-spec overrides the previous settings.For instance, this changes the default fontset to use a font of which family name is `Kochi Gothic' for all characters belonging to the charset
japanese-jisx0208.(set-fontset-font t 'japanese-jisx0208 (font-spec :family "Kochi Gothic"))
This function returns
tif Emacs ought to be able to display char. More precisely, if the selected frame's fontset has a font to display the character set that char belongs to.Fontsets can specify a font on a per-character basis; when the fontset does that, this function's value may not be accurate.
Normally, it is not necessary to manipulate fonts directly. In case you need to do so, this section explains how.
In Emacs Lisp, fonts are represented using three different Lisp object types: font objects, font specs, and font entities.
Return
tif object is a font object, font spec, or font entity. Otherwise, returnnil.The optional argument type, if non-
nil, determines the exact type of Lisp object to check for. In that case, type should be one offont-object,font-spec, orfont-entity.
A font object is a Lisp object that represents a font that Emacs has opened. Font objects cannot be modified in Lisp, but they can be inspected.
Return the font object that is being used to display the character at position position in the window window. If window is
nil, it defaults to the selected window. If string isnil, position specifies a position in the current buffer; otherwise, string should be a string, and position specifies a position in that string.
A font spec is a Lisp object that contains a set of specifications that can be used to find a font. More than one font may match the specifications in a font spec.
Return a new font spec using the specifications in arguments, which should come in
property-valuepairs. The possible specifications are as follows:
:name- The font name (a string), in either XLFD, Fontconfig, or GTK format. See Fonts.
:family:foundry:weight:slant:width- These have the same meanings as the face attributes of the same name. See Face Attributes.
:size- The font size—either a non-negative integer that specifies the pixel size, or a floating-point number that specifies the point size.
:adstyle- Additional typographic style information for the font, such as `sans'. The value should be a string or a symbol.
:registry- The charset registry and encoding of the font, such as `iso8859-1'. The value should be a string or a symbol.
:script- The script that the font must support (a symbol).
:lang- The language that the font should support. The value should be a symbol whose name is a two-letter ISO-639 language name. On X, the value is matched against the “Additional Style” field of the XLFD name of a font, if it is non-empty. On MS-Windows, fonts matching the spec are required to support codepages needed for the language. Currently, only a small set of CJK languages is supported with this property: `ja', `ko', and `zh'.
:otf- The font must be an OpenType font that supports these OpenType features, provided Emacs is compiled with a library, such as `libotf' on GNU/Linux, that supports complex text layout for scripts which need that. The value must be a list of the form
(script-tag langsys-tag gsub gpos)where script-tag is the OpenType script tag symbol; langsys-tag is the OpenType language system tag symbol, or
nilto use the default language system;gsubis a list of OpenType GSUB feature tag symbols, ornilif none is required; andgposis a list of OpenType GPOS feature tag symbols, ornilif none is required. Ifgsuborgposis a list, anilelement in that list means that the font must not match any of the remaining tag symbols. Thegposelement may be omitted.
Set the font property property in the font-spec font-spec to value.
A font entity is a reference to a font that need not be open. Its properties are intermediate between a font object and a font spec: like a font object, and unlike a font spec, it refers to a single, specific font. Unlike a font object, creating a font entity does not load the contents of that font into computer memory. Emacs may open multiple font objects of different sizes from a single font entity referring to a scalable font.
This function returns a font entity that best matches the font spec font-spec on frame frame. If frame is
nil, it defaults to the selected frame.
This function returns a list of all font entities that match the font spec font-spec.
The optional argument frame, if non-
nil, specifies the frame on which the fonts are to be displayed. The optional argument num, if non-nil, should be an integer that specifies the maximum length of the returned list. The optional argument prefer, if non-nil, should be another font spec, which is used to control the order of the returned list; the returned font entities are sorted in order of decreasing closeness to that font spec.
If you call set-face-attribute and pass a font spec, font
entity, or font name string as the value of the :font
attribute, Emacs opens the best matching font that is available
for display. It then stores the corresponding font object as the
actual value of the :font attribute for that face.
The following functions can be used to obtain information about a font. For these functions, the font argument can be a font object, a font entity, or a font spec.
This function returns the value of the font property property for font.
If font is a font spec and the font spec does not specify property, the return value is
nil. If font is a font object or font entity, the value for the :script property may be a list of scripts supported by the font.
This function returns a list of face attributes corresponding to font. The optional argument frame specifies the frame on which the font is to be displayed. If it is
nil, the selected frame is used. The return value has the form(:family family :height height :weight weight :slant slant :width width)where the values of family, height, weight, slant, and width are face attribute values. Some of these key-attribute pairs may be omitted from the list if they are not specified by font.
This function returns the XLFD (X Logical Font Descriptor), a string, matching font. See Fonts, for information about XLFDs. If the name is too long for an XLFD (which can contain at most 255 characters), the function returns
nil.If the optional argument fold-wildcards is non-
nil, consecutive wildcards in the XLFD are folded into one.
The following two functions return important information about a font.
This function returns information about a font specified by its name, a string, as it is used on frame. If frame is omitted or
nil, it defaults to the selected frame.The value returned by the function is a vector of the form
[opened-name full-name size height baseline-offset relative-compose default-ascent max-width ascent descent space-width average-width filename capability]. Here's the description of each components of this vector:
- opened-name
- The name used to open the font, a string.
- full-name
- The full name of the font, a string.
- size
- The pixel size of the font.
- height
- The height of the font in pixels.
- baseline-offset
- The offset in pixels from the ASCII baseline, positive upward.
- relative-compose
- default-ascent
- Numbers controlling how to compose characters.
- ascent
- descent
- The ascent and descent of this font. The sum of these two numbers should be equal to the value of height above.
- space-width
- The width, in pixels, of the font's space character.
- average-width
- The average width of the font characters. If this is zero, Emacs uses the value of space-width instead, when it calculates text layout on display.
- filename
- The file name of the font as a string. This can be
nilif the font back-end does not provide a way to find out the font's file name.
- capability
- A list whose first element is a symbol representing the font type, one of
x,opentype,truetype,type1,pcf, orbdf. For OpenType fonts, the list includes 2 additional elements describing the gsub and gpos features supported by the font. Each of these elements is a list of the form((script(langsys feature...) ...) ...), where script is a symbol representing an OpenType script tag, langsys is a symbol representing an OpenType langsys tag (ornil, which stands for the default langsys), and each feature is a symbol representing an OpenType feature tag.
This function returns information about a font-object. (This is in contrast to
font-info, which takes the font name, a string, as its argument.)The value returned by the function is a vector of the form
[name filename pixel-size max-width ascent descent space-width average-width capability]. Here's the description of each components of this vector:
- name
- The font name, a string.
- filename
- The file name of the font as a string. This can be
nilif the font back-end does not provide a way to find out the font's file name.
- pixel-size
- The pixel size of the font used to open the font.
- max-width
- The maximum advance width of the font.
- ascent
- descent
- The ascent and descent of this font. The sum of these two numbers gives the font height.
- space-width
- The width, in pixels, of the font's space character.
- average-width
- The average width of the font characters. If this is zero, Emacs uses the value of space-width instead, when it calculates text layout on display.
- capability
- A list whose first element is a symbol representing the font type, one of
x,opentype,truetype,type1,pcf, orbdf. For OpenType fonts, the list includes 2 additional elements describing the gsub and gpos features supported by the font. Each of these elements is a list of the form((script(langsys feature...) ...) ...), where script is a symbol representing an OpenType script tag, langsys is a symbol representing an OpenType langsys tag (ornil, which stands for the default langsys), and each feature is a symbol representing an OpenType feature tag.
The following four functions return size information about fonts used by various faces, allowing various layout considerations in Lisp programs. These functions take face remapping into consideration, returning information about the remapped face, if the face in question was remapped. See Face Remapping.
This function returns the average width in pixels of the font used by the current buffer's default face.
This function returns the height in pixels of the font used by the current buffer's default face.
This function returns the average width in pixels for the font used by face in window. The specified window must be a live window. If
nilor omitted, window defaults to the selected window, and face defaults to the default face in window.
This function returns the height in pixels for the font used by face in window. The specified window must be a live window. If
nilor omitted, window defaults to the selected window, and face defaults to the default face in window.
On graphical displays, Emacs draws fringes next to each window: thin vertical strips down the sides which can display bitmaps indicating truncation, continuation, horizontal scrolling, and so on.
The following buffer-local variables control the position and width of fringes in windows showing that buffer.
The fringes normally appear between the display margins and the window text. If the value is non-
nil, they appear outside the display margins. See Display Margins.
This variable, if non-
nil, specifies the width of the left fringe in pixels. A value ofnilmeans to use the left fringe width from the window's frame.
This variable, if non-
nil, specifies the width of the right fringe in pixels. A value ofnilmeans to use the right fringe width from the window's frame.
Any buffer which does not specify values for these variables uses
the values specified by the left-fringe and right-fringe
frame parameters (see Layout Parameters).
The above variables actually take effect via the function
set-window-buffer (see Buffers and Windows), which calls
set-window-fringes as a subroutine. If you change one of these
variables, the fringe display is not updated in existing windows
showing the buffer, unless you call set-window-buffer again in
each affected window. You can also use set-window-fringes to
control the fringe display in individual windows.
This function sets the fringe widths of window window. If window is
nil, the selected window is used.The argument left specifies the width in pixels of the left fringe, and likewise right for the right fringe. A value of
nilfor either one stands for the default width. If outside-margins is non-nil, that specifies that fringes should appear outside of the display margins.
This function returns information about the fringes of a window window. If window is omitted or
nil, the selected window is used. The value has the form(left-width right-width outside-margins).
Fringe indicators are tiny icons displayed in the window fringe to indicate truncated or continued lines, buffer boundaries, etc.
When this is non-
nil, Emacs displays a special glyph in the fringe of each empty line at the end of the buffer, on graphical displays. See Fringes. This variable is automatically buffer-local in every buffer.
This buffer-local variable controls how the buffer boundaries and window scrolling are indicated in the window fringes.
Emacs can indicate the buffer boundaries—that is, the first and last line in the buffer—with angle icons when they appear on the screen. In addition, Emacs can display an up-arrow in the fringe to show that there is text above the screen, and a down-arrow to show there is text below the screen.
There are three kinds of basic values:
nil- Don't display any of these fringe icons.
left- Display the angle icons and arrows in the left fringe.
right- Display the angle icons and arrows in the right fringe.
- any non-alist
- Display the angle icons in the left fringe and don't display the arrows.
Otherwise the value should be an alist that specifies which fringe indicators to display and where. Each element of the alist should have the form
(indicator.position). Here, indicator is one oftop,bottom,up,down, andt(which covers all the icons not yet specified), while position is one ofleft,rightandnil.For example,
((top . left) (t . right))places the top angle bitmap in left fringe, and the bottom angle bitmap as well as both arrow bitmaps in right fringe. To show the angle bitmaps in the left fringe, and no arrow bitmaps, use((top . left) (bottom . left)).
This buffer-local variable specifies the mapping from logical fringe indicators to the actual bitmaps displayed in the window fringes. The value is an alist of elements
(indicator.bitmaps), where indicator specifies a logical indicator type and bitmaps specifies the fringe bitmaps to use for that indicator.Each indicator should be one of the following symbols:
truncation,continuation.- Used for truncation and continuation lines.
up,down,top,bottom,top-bottom- Used when
indicate-buffer-boundariesis non-nil:upanddownindicate a buffer boundary lying above or below the window edge;topandbottomindicate the topmost and bottommost buffer text line; andtop-bottomindicates where there is just one line of text in the buffer.
empty-line- Used to indicate empty lines when
indicate-empty-linesis non-nil.
overlay-arrow- Used for overlay arrows (see Overlay Arrow).
Each bitmaps value may be a list of symbols
(left right[left1 right1]). The left and right symbols specify the bitmaps shown in the left and/or right fringe, for the specific indicator. left1 and right1 are specific to thebottomandtop-bottomindicators, and are used to indicate that the last text line has no final newline. Alternatively, bitmaps may be a single symbol which is used in both left and right fringes.See Fringe Bitmaps, for a list of standard bitmap symbols and how to define your own. In addition,
nilrepresents the empty bitmap (i.e., an indicator that is not shown).When
fringe-indicator-alisthas a buffer-local value, and there is no bitmap defined for a logical indicator, or the bitmap ist, the corresponding value from the default value offringe-indicator-alistis used.
When a line is exactly as wide as the window, Emacs displays the cursor in the right fringe instead of using two lines. Different bitmaps are used to represent the cursor in the fringe depending on the current buffer's cursor type.
If this is non-
nil, lines exactly as wide as the window (not counting the final newline character) are not continued. Instead, when point is at the end of the line, the cursor appears in the right fringe.
This variable specifies the mapping from logical cursor type to the actual fringe bitmaps displayed in the right fringe. The value is an alist where each element has the form
(cursor-type.bitmap), which means to use the fringe bitmap bitmap to display cursors of type cursor-type.Each cursor-type should be one of
box,hollow,bar,hbar, orhollow-small. The first four have the same meanings as in thecursor-typeframe parameter (see Cursor Parameters). Thehollow-smalltype is used instead ofhollowwhen the normalhollow-rectanglebitmap is too tall to fit on a specific display line.Each bitmap should be a symbol specifying the fringe bitmap to be displayed for that logical cursor type. See Fringe Bitmaps.
When
fringe-cursor-alisthas a buffer-local value, and there is no bitmap defined for a cursor type, the corresponding value from the default value offringes-indicator-alistis used.
The fringe bitmaps are the actual bitmaps which represent the
logical fringe indicators for truncated or continued lines, buffer
boundaries, overlay arrows, etc. Each bitmap is represented by a
symbol.
These symbols are referred to by the variable
fringe-indicator-alist, which maps fringe indicators to bitmaps
(see Fringe Indicators), and the variable
fringe-cursor-alist, which maps fringe cursors to bitmaps
(see Fringe Cursors).
Lisp programs can also directly display a bitmap in the left or
right fringe, by using a display property for one of the
characters appearing in the line (see Other Display Specs). Such
a display specification has the form
(fringe bitmap [face])
fringe is either the symbol left-fringe or
right-fringe. bitmap is a symbol identifying the bitmap
to display. The optional face names a face whose foreground
color is used to display the bitmap; this face is automatically merged
with the fringe face.
Here is a list of the standard fringe bitmaps defined in Emacs, and
how they are currently used in Emacs (via
fringe-indicator-alist and fringe-cursor-alist):
left-arrow, right-arrow
left-curly-arrow, right-curly-arrow
right-triangle, left-triangle
up-arrow, down-arrow, top-left-angle top-right-anglebottom-left-angle, bottom-right-angletop-right-angle, top-left-angleleft-bracket, right-bracket, top-right-angle, top-left-angle
filled-rectangle, hollow-rectanglefilled-square, hollow-squarevertical-bar, horizontal-bar
empty-line, exclamation-mark, question-mark, exclamation-mark
The next subsection describes how to define your own fringe bitmaps.
This function returns the fringe bitmaps of the display line containing position pos in window window. The return value has the form
(left right ov), where left is the symbol for the fringe bitmap in the left fringe (ornilif no bitmap), right is similar for the right fringe, and ov is non-nilif there is an overlay arrow in the left fringe.The value is
nilif pos is not visible in window. If window isnil, that stands for the selected window. If pos isnil, that stands for the value of point in window.
This function defines the symbol bitmap as a new fringe bitmap, or replaces an existing bitmap with that name.
The argument bits specifies the image to use. It should be either a string or a vector of integers, where each element (an integer) corresponds to one row of the bitmap. Each bit of an integer corresponds to one pixel of the bitmap, where the low bit corresponds to the rightmost pixel of the bitmap.
The height is normally the length of bits. However, you can specify a different height with non-
nilheight. The width is normally 8, but you can specify a different width with non-nilwidth. The width must be an integer between 1 and 16.The argument align specifies the positioning of the bitmap relative to the range of rows where it is used; the default is to center the bitmap. The allowed values are
top,center, orbottom.The align argument may also be a list
(align periodic)where align is interpreted as described above. If periodic is non-nil, it specifies that the rows inbitsshould be repeated enough times to reach the specified height.
This function destroy the fringe bitmap identified by bitmap. If bitmap identifies a standard fringe bitmap, it actually restores the standard definition of that bitmap, instead of eliminating it entirely.
This sets the face for the fringe bitmap bitmap to face. If face is
nil, it selects thefringeface. The bitmap's face controls the color to draw it in.face is merged with the
fringeface, so normally face should specify only the foreground color.
The overlay arrow is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed. This feature has nothing to do with overlays (see Overlays).
This variable holds the string to display to call attention to a particular line, or
nilif the arrow feature is not in use. On a graphical display the contents of the string are ignored; instead a glyph is displayed in the fringe area to the left of the display area.
This variable holds a marker that indicates where to display the overlay arrow. It should point at the beginning of a line. On a non-graphical display the arrow text appears at the beginning of that line, overlaying any text that would otherwise appear. Since the arrow is usually short, and the line usually begins with indentation, normally nothing significant is overwritten.
The overlay-arrow string is displayed in any given buffer if the value of
overlay-arrow-positionin that buffer points into that buffer. Thus, it is possible to display multiple overlay arrow strings by creating buffer-local bindings ofoverlay-arrow-position. However, it is usually cleaner to useoverlay-arrow-variable-listto achieve this result.
You can do a similar job by creating an overlay with a
before-string property. See Overlay Properties.
You can define multiple overlay arrows via the variable
overlay-arrow-variable-list.
This variable's value is a list of variables, each of which specifies the position of an overlay arrow. The variable
overlay-arrow-positionhas its normal meaning because it is on this list.
Each variable on this list can have properties
overlay-arrow-string and overlay-arrow-bitmap that
specify an overlay arrow string (for text terminals) or fringe bitmap
(for graphical terminals) to display at the corresponding overlay
arrow position. If either property is not set, the default
overlay-arrow-string or overlay-arrow fringe indicator
is used.
Normally the frame parameter vertical-scroll-bars controls
whether the windows in the frame have vertical scroll bars, and whether
they are on the left or right. The frame parameter
scroll-bar-width specifies how wide they are (nil meaning
the default).
The frame parameter horizontal-scroll-bars controls whether
the windows in the frame have horizontal scroll bars. The frame
parameter scroll-bar-height specifies how high they are
(nil meaning the default). See Layout Parameters.
Horizontal scroll bars are not available on all platforms. The
function horizontal-scroll-bars-available-p which takes no
argument returns non-nil if they are available on your system.
The following three functions take as argument a live frame which defaults to the selected one.
This function reports the scroll bar types for frame frame. The value is a cons cell
(vertical-type.horizontal-type), where vertical-type is eitherleft,right, ornil(which means no vertical scroll bar.) horizontal-type is eitherbottomornil(which means no horizontal scroll bar).
This function returns the width of vertical scroll bars of frame in pixels.
This function returns the height of horizontal scroll bars of frame in pixels.
You can override the frame specific settings for individual windows by using the following function:
This function sets the width and/or height and the types of scroll bars for window window.
width specifies the width of the vertical scroll bar in pixels (
nilmeans use the width specified for the frame). vertical-type specifies whether to have a vertical scroll bar and, if so, where. The possible values areleft,right,t, which means to use the frame's default, andnilfor no vertical scroll bar.height specifies the height of the horizontal scroll bar in pixels (
nilmeans use the height specified for the frame). horizontal-type specifies whether to have a horizontal scroll bar. The possible values arebottom,t, which means to use the frame's default, andnilfor no horizontal scroll bar.If window is
nil, the selected window is used.
The following four functions take as argument a live window which defaults to the selected one.
This function returns a list of the form
(width columns vertical-type height lines horizontal-type).The value width is the value that was specified for the width of the vertical scroll bar (which may be
nil); columns is the (possibly rounded) number of columns that the vertical scroll bar actually occupies.The value height is the value that was specified for the height of the horizontal scroll bar (which may be
nil); lines is the (possibly rounded) number of lines that the horizontally scroll bar actually occupies.
This function reports the scroll bar type for window window. The value is a cons cell
(vertical-type.horizontal-type). Unlikewindow-scroll-bars, this reports the scroll bar type actually used, once frame defaults andscroll-bar-modeare taken into account.
This function returns the width in pixels of window's vertical scrollbar.
This function returns the height in pixels of window's horizontal scrollbar.
If you don't specify these values for a window with
set-window-scroll-bars, the buffer-local variables
vertical-scroll-bar, horizontal-scroll-bar,
scroll-bar-width and scroll-bar-height in the buffer being
displayed control the window's scroll bars. The function
set-window-buffer examines these variables. If you change them
in a buffer that is already visible in a window, you can make the window
take note of the new values by calling set-window-buffer
specifying the same buffer that is already displayed.
You can control the appearance of scroll bars for a particular buffer by setting the following variables which automatically become buffer-local when set.
This variable specifies the location of the vertical scroll bar. The possible values are
left,right,t, which means to use the frame's default, andnilfor no scroll bar.
This variable specifies the location of the horizontal scroll bar. The possible values are
bottom,t, which means to use the frame's default, andnilfor no scroll bar.
This variable specifies the width of the buffer's vertical scroll bars, measured in pixels. A value of
nilmeans to use the value specified by the frame.
This variable specifies the height of the buffer's horizontal scroll bar, measured in pixels. A value of
nilmeans to use the value specified by the frame.
Finally you can toggle the display of scroll bars on all frames by
customizing the variables scroll-bar-mode and
horizontal-scroll-bar-mode.
This variable controls whether and where to put vertical scroll bars in all frames. The possible values are
nilfor no scroll bars,leftto put scroll bars on the left andrightto put scroll bars on the right.
This variable controls whether to display horizontal scroll bars on all frames.
Window dividers are bars drawn between a frame's windows. A right
divider is drawn between a window and any adjacent windows on the right.
Its width (thickness) is specified by the frame parameter
right-divider-width. A bottom divider is drawn between a
window and adjacent windows on the bottom or the echo area. Its width
is specified by the frame parameter bottom-divider-width. In
either case, specifying a width of zero means to not draw such dividers.
See Layout Parameters.
Technically, a right divider belongs to the window on its left, which means that its width contributes to the total width of that window. A bottom divider belongs to the window above it, which means that its width contributes to the total height of that window. See Window Sizes. When a window has both, a right and a bottom divider, the bottom divider prevails. This means that a bottom divider is drawn over the full total width of its window while the right divider ends above the bottom divider.
Dividers can be dragged with the mouse and are therefore useful for adjusting the sizes of adjacent windows with the mouse. They also serve to visually set apart adjacent windows when no scroll bars or mode lines are present. The following three faces allow the customization of the appearance of dividers:
window-dividerwindow-divider-first-pixelwindow-divider face.
window-divider-last-pixelwindow-divider face.
You can get the sizes of the dividers of a specific window with the following two functions.
Return the width (thickness) in pixels of window's right divider. window must be a live window and defaults to the selected one. The return value is always zero for a rightmost window.
Return the width (thickness) in pixels of window's bottom divider. window must be a live window and defaults to the selected one. The return value is zero for the minibuffer window or a bottommost window on a minibuffer-less frame.
display Property
The display text property (or overlay property) is used to
insert images into text, and to control other aspects of how text
displays. The value of the display property should be a
display specification, or a list or vector containing several display
specifications. Display specifications in the same display
property value generally apply in parallel to the text they cover.
If several sources (overlays and/or a text property) specify values
for the display property, only one of the values takes effect,
following the rules of get-char-property. See Examining Properties.
The rest of this section describes several kinds of display specifications and what they mean.
Some kinds of display specifications specify something to display instead of the text that has the property. These are called replacing display specifications. Emacs does not allow the user to interactively move point into the middle of buffer text that is replaced in this way.
If a list of display specifications includes more than one replacing display specification, the first overrides the rest. Replacing display specifications make most other display specifications irrelevant, since those don't apply to the replacement.
For replacing display specifications, the text that has the
property means all the consecutive characters that have the same
Lisp object as their display property; these characters are
replaced as a single unit. If two characters have different Lisp
objects as their display properties (i.e., objects which are
not eq), they are handled separately.
Here is an example which illustrates this point. A string serves as a replacing display specification, which replaces the text that has the property with the specified string (see Other Display Specs). Consider the following function:
(defun foo ()
(dotimes (i 5)
(let ((string (concat "A"))
(start (+ i i (point-min))))
(put-text-property start (1+ start) 'display string)
(put-text-property start (+ 2 start) 'display string))))
This function gives each of the first ten characters in the buffer a
display property which is a string "A", but they don't
all get the same string object. The first two characters get the same
string object, so they are replaced with one `A'; the fact that
the display property was assigned in two separate calls to
put-text-property is irrelevant. Similarly, the next two
characters get a second string (concat creates a new string
object), so they are replaced with one `A'; and so on. Thus, the
ten characters appear as five A's.
To display a space of specified width and/or height, use a display
specification of the form (space . props), where
props is a property list (a list of alternating properties and
values). You can put this property on one or more consecutive
characters; a space of the specified height and width is displayed in
place of all of those characters. These are the properties you
can use in props to specify the weight of the space:
:width width
:relative-width factor
display property. The space width is the pixel width of
that character, multiplied by factor. (On text-mode terminals,
the “pixel width” of a character is usually 1, but it could be more
for TABs and double-width CJK characters.)
:align-to hpos
You should use one and only one of the above properties. You can also specify the height of the space, with these properties:
:height height
:relative-height factor
:ascent ascent
Don't use both :height and :relative-height together.
The :width and :align-to properties are supported on
non-graphic terminals, but the other space properties in this section
are not.
Note that space properties are treated as paragraph separators for the purposes of reordering bidirectional text for display. See Bidirectional Display, for the details.
The value of the :width, :align-to, :height,
and :ascent properties can be a special kind of expression that
is evaluated during redisplay. The result of the evaluation is used
as an absolute number of pixels.
The following expressions are supported:
expr ::= num | (num) | unit | elem | pos | image | form
num ::= integer | float | symbol
unit ::= in | mm | cm | width | height
elem ::= left-fringe | right-fringe | left-margin | right-margin
| scroll-bar | text
pos ::= left | center | right
form ::= (num . expr) | (op expr ...)
op ::= + | -
The form num specifies a fraction of the default frame font
height or width. The form (num) specifies an absolute
number of pixels. If num is a symbol, symbol, its
buffer-local variable binding is used.
The in, mm, and cm units specify the number of
pixels per inch, millimeter, and centimeter, respectively. The
width and height units correspond to the default width
and height of the current face. An image specification image
corresponds to the width or height of the image.
The elements left-fringe, right-fringe,
left-margin, right-margin, scroll-bar, and
text specify to the width of the corresponding area of the
window.
The left, center, and right positions can be
used with :align-to to specify a position relative to the left
edge, center, or right edge of the text area.
Any of the above window elements (except text) can also be
used with :align-to to specify that the position is relative to
the left edge of the given area. Once the base offset for a relative
position has been set (by the first occurrence of one of these
symbols), further occurrences of these symbols are interpreted as the
width of the specified area. For example, to align to the center of
the left-margin, use
:align-to (+ left-margin (0.5 . left-margin))
If no specific base offset is set for alignment, it is always relative to the left edge of the text area. For example, `:align-to 0' in a header-line aligns with the first text column in the text area.
A value of the form (num . expr) stands for the
product of the values of num and expr. For example,
(2 . in) specifies a width of 2 inches, while (0.5 .
image) specifies half the width (or height) of the specified
image.
The form (+ expr ...) adds up the value of the
expressions. The form (- expr ...) negates or subtracts
the value of the expressions.
Here are the other sorts of display specifications that you can use
in the display text property.
Recursive display specifications are not supported—string's
display properties, if any, are not used.
(image . image-props)
(slice x y width height)
image specifies a slice
(a partial area) of the image to display. The elements y and
x specify the top left corner of the slice, within the image;
width and height specify the width and height of the
slice. Integers are numbers of pixels. A floating-point number
in the range 0.0–1.0 stands for that fraction of the width or height
of the entire image.
((margin nil) string)
(left-fringe bitmap [face])(right-fringe bitmap [face])
(space-width factor)
(height height)
(+ n)
(- n)
height bound to the current specified font height.
(raise factor)
factor must be a number, which is interpreted as a multiple of the height of the affected text. If it is positive, that means to display the characters raised. If it is negative, that means to display them lower down.
If the text also has a height display specification, that does
not affect the amount of raising or lowering, which is based on the
faces used for the text.
You can make any display specification conditional. To do that,
package it in another list of the form
(when condition . spec).
Then the specification spec applies only when
condition evaluates to a non-nil value. During the
evaluation, object is bound to the string or buffer having the
conditional display property. position and
buffer-position are bound to the position within object
and the buffer position where the display property was found,
respectively. Both positions can be different when object is a
string.
A buffer can have blank areas called display margins on the
left and on the right. Ordinary text never appears in these areas,
but you can put things into the display margins using the
display property. There is currently no way to make text or
images in the margin mouse-sensitive.
The way to display something in the margins is to specify it in a
margin display specification in the display property of some
text. This is a replacing display specification, meaning that the
text you put it on does not get displayed; the margin display appears,
but that text does not.
A margin display specification looks like ((margin
right-margin) spec) or ((margin left-margin) spec).
Here, spec is another display specification that says what to
display in the margin. Typically it is a string of text to display,
or an image descriptor.
To display something in the margin in association with
certain buffer text, without altering or preventing the display of
that text, put a before-string property on the text and put the
margin display specification on the contents of the before-string.
Before the display margins can display anything, you must give them a nonzero width. The usual way to do that is to set these variables:
This variable specifies the width of the left margin, in character cell (a.k.a. “column”) units. It is buffer-local in all buffers. A value of
nilmeans no left marginal area.
This variable specifies the width of the right margin, in character cell units. It is buffer-local in all buffers. A value of
nilmeans no right marginal area.
Setting these variables does not immediately affect the window. These
variables are checked when a new buffer is displayed in the window.
Thus, you can make changes take effect by calling
set-window-buffer.
You can also set the margin widths immediately.
This function specifies the margin widths for window window, in character cell units. The argument left controls the left margin, and right controls the right margin (default
0).
This function returns the width of the left and right margins of window as a cons cell of the form
(left.right). If one of the two marginal areas does not exist, its width is returned asnil; if neither of the two margins exist, the function returns(nil). If window isnil, the selected window is used.
To display an image in an Emacs buffer, you must first create an image
descriptor, then use it as a display specifier in the display
property of text that is displayed (see Display Property).
Emacs is usually able to display images when it is run on a
graphical terminal. Images cannot be displayed in a text terminal, on
certain graphical terminals that lack the support for this, or if
Emacs is compiled without image support. You can use the function
display-images-p to determine if images can in principle be
displayed (see Display Feature Testing).
Emacs can display a number of different image formats. Some of
these image formats are supported only if particular support libraries
are installed. On some platforms, Emacs can load support libraries on
demand; if so, the variable dynamic-library-alist can be used
to modify the set of known names for these dynamic libraries.
See Dynamic Libraries.
Supported image formats (and the required support libraries) include
PBM and XBM (which do not depend on support libraries and are always
available), XPM (libXpm), GIF (libgif or
libungif), PostScript (gs), JPEG (libjpeg), TIFF
(libtiff), PNG (libpng), and SVG (librsvg).
Each of these image formats is associated with an image type
symbol. The symbols for the above formats are, respectively,
pbm, xbm, xpm, gif, postscript,
jpeg, tiff, png, and svg.
Furthermore, if you build Emacs with ImageMagick
(libMagickWand) support, Emacs can display any image format
that ImageMagick can. See ImageMagick Images. All images
displayed via ImageMagick have type symbol imagemagick.
This variable contains a list of type symbols for image formats which are potentially supported in the current configuration.
“Potentially” means that Emacs knows about the image types, not necessarily that they can be used (for example, they could depend on unavailable dynamic libraries). To know which image types are really available, use
image-type-available-p.
This function returns non-
nilif images of type type can be loaded and displayed. type must be an image type symbol.For image types whose support libraries are statically linked, this function always returns
t. For image types whose support libraries are dynamically loaded, it returnstif the library could be loaded andnilotherwise.
An image descriptor is a list which specifies the underlying
data for an image, and how to display it. It is typically used as the
value of a display overlay or text property (see Other Display Specs); but See Showing Images, for convenient helper
functions to insert images into buffers.
Each image descriptor has the form (image . props),
where props is a property list of alternating keyword symbols
and values, including at least the pair :type type that
specifies the image type.
The following is a list of properties that are meaningful for all image types (there are also properties which are meaningful only for certain image types, as documented in the following subsections):
:type type
:file file
data-directory.
:data data
:data or :file, but not both.
For most image types, the value of a :data property should be a
string containing the image data. Some image types do not support
:data; for some others, :data alone is not enough, so
you need to use other image properties along with :data. See
the following subsections for details.
:margin margin
(x . y) of such numbers. If it is a pair,
x specifies how many pixels to add horizontally, and y
specifies how many pixels to add vertically. If :margin is not
specified, the default is zero.
:ascent ascent
center.
If ascent is a number, that percentage of the image's height is used for its ascent.
If ascent is center, the image is vertically centered
around a centerline which would be the vertical centerline of text drawn
at the position of the image, in the manner specified by the text
properties and overlays that apply to the image.
If this property is omitted, it defaults to 50.
:relief relief
:conversion algorithm
laplaceemboss(edge-detection :matrix matrix :color-adjust adjust)
(x-1/y-1 x/y-1 x+1/y-1
x-1/y x/y x+1/y
x-1/y+1 x/y+1 x+1/y+1)
The resulting pixel is computed from the color intensity of the color resulting from summing up the RGB values of surrounding pixels, multiplied by the specified factors, and dividing that sum by the sum of the factors' absolute values.
Laplace edge-detection currently uses a matrix of
(1 0 0
0 0 0
0 0 -1)
Emboss edge-detection uses a matrix of
( 2 -1 0
-1 0 1
0 1 -2)
disabled:mask mask
heuristic or (heuristic bg), build
a clipping mask for the image, so that the background of a frame is
visible behind the image. If bg is not specified, or if bg
is t, determine the background color of the image by looking at
the four corners of the image, assuming the most frequently occurring
color from the corners is the background color of the image. Otherwise,
bg must be a list (red green blue)
specifying the color to assume for the background of the image.
If mask is nil, remove a mask from the image, if it has
one. Images in some formats include a mask which can be removed by
specifying :mask nil.
:pointer shape
:map map
An image map is an alist where each element has the format
(area id plist). An area is specified
as either a rectangle, a circle, or a polygon.
A rectangle is a cons
(rect . ((x0 . y0) . (x1 . y1)))
which specifies the pixel coordinates of the upper left and bottom right
corners of the rectangle area.
A circle is a cons
(circle . ((x0 . y0) . r))
which specifies the center and the radius of the circle; r may
be a float or integer.
A polygon is a cons
(poly . [x0 y0 x1 y1 ...])
where each pair in the vector describes one corner in the polygon.
When the mouse pointer lies on a hot-spot area of an image, the
plist of that hot-spot is consulted; if it contains a help-echo
property, that defines a tool-tip for the hot-spot, and if it contains
a pointer property, that defines the shape of the mouse cursor when
it is on the hot-spot.
See Pointer Shape, for available pointer shapes.
When you click the mouse when the mouse pointer is over a hot-spot, an
event is composed by combining the id of the hot-spot with the
mouse event; for instance, [area4 mouse-1] if the hot-spot's
id is area4.
This function returns
tif image spec has a mask bitmap. frame is the frame on which the image will be displayed. framenilor omitted means to use the selected frame (see Input Focus).
To use XBM format, specify xbm as the image type. This image
format doesn't require an external library, so images of this type are
always supported.
Additional image properties supported for the xbm image type are:
:foreground foreground
nil for the default color. This color is
used for each pixel in the XBM that is 1. The default is the frame's
foreground color.
:background background
nil for the default color. This color is
used for each pixel in the XBM that is 0. The default is the frame's
background color.
If you specify an XBM image using data within Emacs instead of an external file, use the following three properties:
:data data
:height and :width.
:height and :width in this case,
because omitting them is what indicates the data has the format of an
XBM file. The file contents specify the height and width of the image.
height bits. In this case, you must specify
:height and :width, both to indicate that the string
contains just the bits rather than a whole XBM file, and to specify the
size of the image.
:width width
:height height
To use XPM format, specify xpm as the image type. The
additional image property :color-symbols is also meaningful with
the xpm image type:
:color-symbols symbols
(name . color). In each element, name is
the name of a color as it appears in the image file, and color
specifies the actual color to use for displaying that name.
To use PostScript for an image, specify image type postscript.
This works only if you have Ghostscript installed. You must always use
these three properties:
:pt-width width
:pt-height height
:bounding-box box
%%BoundingBox: 22 171 567 738
If you build Emacs with ImageMagick support, you can use the
ImageMagick library to load many image formats (see File Conveniences). The image type symbol
for images loaded via ImageMagick is imagemagick, regardless of
the actual underlying image format.
This function returns a list of image file extensions supported by the current ImageMagick installation. Each list element is a symbol representing an internal ImageMagick name for an image type, such as
BMPfor .bmp images.
The value of this variable is a list of ImageMagick image types which Emacs may attempt to render using ImageMagick. Each list element should be one of the symbols in the list returned by
imagemagick-types, or an equivalent string. Alternatively, a value oftenables ImageMagick for all possible image types. Regardless of the value of this variable,imagemagick-types-inhibit(see below) takes precedence.
The value of this variable lists the ImageMagick image types which should never be rendered using ImageMagick, regardless of the value of
imagemagick-enabled-types. A value oftdisables ImageMagick entirely.
This variable is an alist mapping image types to file name extensions. Emacs uses this in conjunction with the
:formatimage property (see below) to give a hint to the ImageMagick library as to the type of an image. Each element has the form(type extension), where type is a symbol specifying an image content-type, and extension is a string that specifies the associated file name extension.
Images loaded with ImageMagick support the following additional image descriptor properties:
:background background
nil, should be a string specifying a
color, which is used as the image's background color if the image
supports transparency. If the value is nil, it defaults to the
frame's background color.
:width width, :height height
:width and :height keywords are used for scaling the
image. If only one of them is specified, the other one will be
calculated so as to preserve the aspect ratio. If both are specified,
aspect ratio may not be preserved.
:max-width max-width, :max-height max-height
:max-width and :max-height keywords are used for
scaling if the size of the image of the image exceeds these values.
If :width is set it will have precedence over max-width,
and if :height is set it will have precedence over
max-height, but you can otherwise mix these keywords as you
wish. :max-width and :max-height will always preserve
the aspect ratio.
:format type
image-format-suffixes. This is used
when the image does not have an associated file name, to provide a
hint to ImageMagick to help it detect the image type.
:rotation angle
:index frame
For PBM images, specify image type pbm. Color, gray-scale and
monochromatic images are supported. For mono PBM images, two additional
image properties are supported.
:foreground foreground
nil for the default color. This color is
used for each pixel in the PBM that is 1. The default is the frame's
foreground color.
:background background
nil for the default color. This color is
used for each pixel in the PBM that is 0. The default is the frame's
background color.
The remaining image types that Emacs can support are:
gif.
Supports the :index property. See Multi-Frame Images.
jpeg.
png.
svg.
tiff.
Supports the :index property. See Multi-Frame Images.
The functions create-image, defimage and
find-image provide convenient ways to create image descriptors.
This function creates and returns an image descriptor which uses the data in file-or-data. file-or-data can be a file name or a string containing the image data; data-p should be
nilfor the former case, non-nilfor the latter case.The optional argument type is a symbol specifying the image type. If type is omitted or
nil,create-imagetries to determine the image type from the file's first few bytes, or else from the file's name.The remaining arguments, props, specify additional image properties—for example,
(create-image "foo.xpm" 'xpm nil :heuristic-mask t)The function returns
nilif images of this type are not supported. Otherwise it returns an image descriptor.
This macro defines symbol as an image name. The arguments specs is a list which specifies how to display the image. The third argument, doc, is an optional documentation string.
Each argument in specs has the form of a property list, and each one should specify at least the
:typeproperty and either the:fileor the:dataproperty. The value of:typeshould be a symbol specifying the image type, the value of:fileis the file to load the image from, and the value of:datais a string containing the actual image data. Here is an example:(defimage test-image ((:type xpm :file "~/test1.xpm") (:type xbm :file "~/test1.xbm")))
defimagetests each argument, one by one, to see if it is usable—that is, if the type is supported and the file exists. The first usable argument is used to make an image descriptor which is stored in symbol.If none of the alternatives will work, then symbol is defined as
nil.
This function provides a convenient way to find an image satisfying one of a list of image specifications specs.
Each specification in specs is a property list with contents depending on image type. All specifications must at least contain the properties
:typetype and either:filefile or:datadata, where type is a symbol specifying the image type, e.g.,xbm, file is the file to load the image from, and data is a string containing the actual image data. The first specification in the list whose type is supported, and file exists, is used to construct the image specification to be returned. If no specification is satisfied,nilis returned.The image is looked for in
image-load-path.
This variable's value is a list of locations in which to search for image files. If an element is a string or a variable symbol whose value is a string, the string is taken to be the name of a directory to search. If an element is a variable symbol whose value is a list, that is taken to be a list of directory names to search.
The default is to search in the images subdirectory of the directory specified by
data-directory, then the directory specified bydata-directory, and finally in the directories inload-path. Subdirectories are not automatically included in the search, so if you put an image file in a subdirectory, you have to supply the subdirectory name explicitly. For example, to find the image images/foo/bar.xpm withindata-directory, you should specify the image as follows:(defimage foo-image '((:type xpm :file "foo/bar.xpm")))
This function returns a suitable search path for images used by the Lisp package library.
The function searches for image first using
image-load-path, excludingdata-directory/images, and then inload-path, followed by a path suitable for library, which includes ../../etc/images and ../etc/images relative to the library file itself, and finally indata-directory/images.Then this function returns a list of directories which contains first the directory in which image was found, followed by the value of
load-path. If path is given, it is used instead ofload-path.If no-error is non-
niland a suitable path can't be found, don't signal an error. Instead, return a list of directories as before, except thatnilappears in place of the image directory.Here is an example of using
image-load-path-for-library:(defvar image-load-path) ; shush compiler (let* ((load-path (image-load-path-for-library "mh-e" "mh-logo.xpm")) (image-load-path (cons (car load-path) image-load-path))) (mh-tool-bar-folder-buttons-init))
You can use an image descriptor by setting up the display
property yourself, but it is easier to use the functions in this
section.
This function inserts image in the current buffer at point. The value image should be an image descriptor; it could be a value returned by
create-image, or the value of a symbol defined withdefimage. The argument string specifies the text to put in the buffer to hold the image. If it is omitted ornil,insert-imageuses" "by default.The argument area specifies whether to put the image in a margin. If it is
left-margin, the image appears in the left margin;right-marginspecifies the right margin. If area isnilor omitted, the image is displayed at point within the buffer's text.The argument slice specifies a slice of the image to insert. If slice is
nilor omitted the whole image is inserted. Otherwise, slice is a list(x y width height)which specifies the x and y positions and width and height of the image area to insert. Integer values are in units of pixels. A floating-point number in the range 0.0–1.0 stands for that fraction of the width or height of the entire image.Internally, this function inserts string in the buffer, and gives it a
displayproperty which specifies image. See Display Property.
This function inserts image in the current buffer at point, like
insert-image, but splits the image into rowsxcols equally sized slices.Emacs displays each slice as a separate image, and allows more intuitive scrolling up/down, instead of jumping up/down the entire image when paging through a buffer that displays (large) images.
This function puts image image in front of pos in the current buffer. The argument pos should be an integer or a marker. It specifies the buffer position where the image should appear. The argument string specifies the text that should hold the image as an alternative to the default.
The argument image must be an image descriptor, perhaps returned by
create-imageor stored bydefimage.The argument area specifies whether to put the image in a margin. If it is
left-margin, the image appears in the left margin;right-marginspecifies the right margin. If area isnilor omitted, the image is displayed at point within the buffer's text.Internally, this function creates an overlay, and gives it a
before-stringproperty containing text that has adisplayproperty whose value is the image. (Whew!)
This function removes images in buffer between positions start and end. If buffer is omitted or
nil, images are removed from the current buffer.This removes only images that were put into buffer the way
put-imagedoes it, not images that were inserted withinsert-imageor in other ways.
This function returns the size of an image as a pair
(width.height). spec is an image specification. pixels non-nilmeans return sizes measured in pixels, otherwise return sizes measured in the default character size of frame (see Frame Font). frame is the frame on which the image will be displayed. frame null or omitted means use the selected frame (see Input Focus).
This variable is used to define the maximum size of image that Emacs will load. Emacs will refuse to load (and display) any image that is larger than this limit.
If the value is an integer, it directly specifies the maximum image height and width, measured in pixels. If it is floating point, it specifies the maximum image height and width as a ratio to the frame height and width. If the value is non-numeric, there is no explicit limit on the size of images.
The purpose of this variable is to prevent unreasonably large images from accidentally being loaded into Emacs. It only takes effect the first time an image is loaded. Once an image is placed in the image cache, it can always be displayed, even if the value of
max-image-sizeis subsequently changed (see Image Cache).
Some image files can contain more than one image. We say that there are multiple “frames” in the image. At present, Emacs supports multiple frames for GIF, TIFF, and certain ImageMagick formats such as DJVM.
The frames can be used either to represent multiple pages (this is usually the case with multi-frame TIFF files, for example), or to create animation (usually the case with multi-frame GIF files).
A multi-frame image has a property :index, whose value is an
integer (counting from 0) that specifies which frame is being displayed.
This function returns non-
nilif image contains more than one frame. The actual return value is a cons(nimages.delay), where nimages is the number of frames and delay is the delay in seconds between them, ornilif the image does not specify a delay. Images that are intended to be animated usually specify a frame delay, whereas ones that are intended to be treated as multiple pages do not.
This function returns the index of the current frame number for image, counting from 0.
This function switches image to frame number n. It replaces a frame number outside the valid range with that of the end of the range, unless nocheck is non-
nil. If image does not contain a frame with the specified number, the image displays as a hollow box.
This function animates image. The optional integer index specifies the frame from which to start (default 0). The optional argument limit controls the length of the animation. If omitted or
nil, the image animates once only; iftit loops forever; if a number animation stops after that many seconds.
Animation operates by means of a timer. Note that Emacs imposes a
minimum frame delay of 0.01 (image-minimum-frame-delay) seconds.
If the image itself does not specify a delay, Emacs uses
image-default-frame-delay.
This function returns the timer responsible for animating image, if there is one.
Emacs caches images so that it can display them again more
efficiently. When Emacs displays an image, it searches the image
cache for an existing image specification equal to the desired
specification. If a match is found, the image is displayed from the
cache. Otherwise, Emacs loads the image normally.
This function removes the image with specification spec from the image cache of frame frame. Image specifications are compared using
equal. If frame isnil, it defaults to the selected frame. If frame ist, the image is flushed on all existing frames.In Emacs's current implementation, each graphical terminal possesses an image cache, which is shared by all the frames on that terminal (see Multiple Terminals). Thus, refreshing an image in one frame also refreshes it in all other frames on the same terminal.
One use for image-flush is to tell Emacs about a change in an
image file. If an image specification contains a :file
property, the image is cached based on the file's contents when the
image is first displayed. Even if the file subsequently changes,
Emacs continues displaying the old version of the image. Calling
image-flush flushes the image from the cache, forcing Emacs to
re-read the file the next time it needs to display that image.
Another use for image-flush is for memory conservation. If
your Lisp program creates a large number of temporary images over a
period much shorter than image-cache-eviction-delay (see
below), you can opt to flush unused images yourself, instead of
waiting for Emacs to do it automatically.
This function clears an image cache, removing all the images stored in it. If filter is omitted or
nil, it clears the cache for the selected frame. If filter is a frame, it clears the cache for that frame. If filter ist, all image caches are cleared. Otherwise, filter is taken to be a file name, and all images associated with that file name are removed from all image caches.
If an image in the image cache has not been displayed for a specified period of time, Emacs removes it from the cache and frees the associated memory.
This variable specifies the number of seconds an image can remain in the cache without being displayed. When an image is not displayed for this length of time, Emacs removes it from the image cache.
Under some circumstances, if the number of images in the cache grows too large, the actual eviction delay may be shorter than this.
If the value is
nil, Emacs does not remove images from the cache except when you explicitly clear it. This mode can be useful for debugging.
Emacs is able to display native widgets, such as GTK WebKit widgets,
in Emacs buffers when it was built with the necessary support
libraries and is running on a graphical terminal. To test whether
Emacs supports display of embedded widgets, check that the
xwidget-internal feature is available (see Named Features).
To display an embedded widget in a buffer, you must first create an
xwidget object, and then use that object as the display specifier
in a display text or overlay property (see Display Property).
This creates and returns an xwidget object. If buffer is omitted or
nil, it defaults to the current buffer. If buffer names a buffer that doesn't exist, it will be created. The type identifies the type of the xwidget component, it can be one of the following:
webkit- The WebKit component.
The width and height arguments specify the widget size in pixels, and title, a string, specifies its title.
This function replaces the property list of xwidget with a new property list given by plist.
This function returns a list of xwidget objects associated with the buffer, which can be specified as a buffer object or a name of an existing buffer, a string. The value is
nilif buffer contains no xwidgets.
This function browses the specified uri in the given xwidget. The uri is a string that specifies the name of a file or a URL.
This function causes the browser widget specified by xwidget to execute the specified JavaScript
script.
This function executes the specified script like
xwidget-webkit-execute-scriptdoes, but it also returns the script's return value as a string. If script doesn't return a value, this function returns default, ornilif default was omitted.
This function returns the title of xwidget as a string.
This function resizes the specified xwidget to the size widthxheight pixels.
This function returns the desired size of xwidget as a list of the form
(width height). The dimensions are in pixels.
This function returns the attributes of xwidget as a vector of the form
[type title width height]. The attributes are usually determined bymake-xwidgetwhen the xwidget is created.
This function allows you to arrange that Emacs will ask the user for confirmation before exiting or before killing a buffer that has xwidget associated with it. If flag is non-
nil, Emacs will query the user, otherwise it will not.
This function returns the current setting of xwidgets query-on-exit flag, either
tornil.
The Button package defines functions for inserting and manipulating buttons that can be activated with the mouse or via keyboard commands. These buttons are typically used for various kinds of hyperlinks.
A button is essentially a set of text or overlay properties, attached to a stretch of text in a buffer. These properties are called button properties. One of these properties, the action property, specifies a function which is called when the user invokes the button using the keyboard or the mouse. The action function may examine the button and use its other properties as desired.
In some ways, the Button package duplicates the functionality in the Widget package. See Introduction. The advantage of the Button package is that it is faster, smaller, and simpler to program. From the point of view of the user, the interfaces produced by the two packages are very similar.
Each button has an associated list of properties defining its appearance and behavior, and other arbitrary properties may be used for application specific purposes. The following properties have special meaning to the Button package:
actionignore,
which does nothing.
mouse-actionaction, and when present, will be used
instead of action for button invocations resulting from
mouse-clicks (instead of the user hitting <RET>). If not
present, mouse-clicks use action instead.
facebutton face.
mouse-facehighlight face.
keymapbutton-map, which defines <RET> and
<mouse-2> to invoke the button.
typehelp-echo"mouse-2, RET: Push this button".
follow-linkbuttonnil button property, which may be useful
in finding regions of text that comprise buttons (which is what the
standard button functions do).
There are other properties defined for the regions of text in a button, but these are not generally interesting for typical uses.
Every button has a button type, which defines default values for the button's properties. Button types are arranged in a hierarchy, with specialized types inheriting from more general types, so that it's easy to define special-purpose types of buttons for specific tasks.
Define a button type called name (a symbol). The remaining arguments form a sequence of property value pairs, specifying default property values for buttons with this type (a button's type may be set by giving it a
typeproperty when creating the button, using the:typekeyword argument).In addition, the keyword argument
:supertypemay be used to specify a button-type from which name inherits its default property values. Note that this inheritance happens only when name is defined; subsequent changes to a supertype are not reflected in its subtypes.
Using define-button-type to define default properties for
buttons is not necessary—buttons without any specified type use the
built-in button-type button—but it is encouraged, since
doing so usually makes the resulting code clearer and more efficient.
Buttons are associated with a region of text, using an overlay or
text properties to hold button-specific information, all of which are
initialized from the button's type (which defaults to the built-in
button type button). Like all Emacs text, the appearance of
the button is governed by the face property; by default (via
the face property inherited from the button button-type)
this is a simple underline, like a typical web-page link.
For convenience, there are two sorts of button-creation functions,
those that add button properties to an existing region of a buffer,
called make-...button, and those that also insert the button
text, called insert-...button.
The button-creation functions all take the &rest argument
properties, which should be a sequence of property value
pairs, specifying properties to add to the button; see Button Properties. In addition, the keyword argument :type may be
used to specify a button-type from which to inherit other properties;
see Button Types. Any properties not explicitly specified
during creation will be inherited from the button's type (if the type
defines such a property).
The following functions add a button using an overlay (see Overlays) to hold the button properties:
This makes a button from beg to end in the current buffer, and returns it.
This insert a button with the label label at point, and returns it.
The following functions are similar, but using text properties (see Text Properties) to hold the button properties. Such buttons do not add markers to the buffer, so editing in the buffer does not slow down if there is an extremely large numbers of buttons. However, if there is an existing face text property on the text (e.g., a face assigned by Font Lock mode), the button face may not be visible. Both of these functions return the starting position of the new button.
This makes a button from beg to end in the current buffer, using text properties.
This inserts a button with the label label at point, using text properties.
These are functions for getting and setting properties of buttons. Often these are used by a button's invocation function to determine what to do.
Where a button parameter is specified, it means an object referring to a specific button, either an overlay (for overlay buttons), or a buffer-position or marker (for text property buttons). Such an object is passed as the first argument to a button's invocation function when it is invoked.
Call button's
actionproperty (i.e., invoke the function that is the value of that property, passing it the single argument button). If use-mouse-action is non-nil, try to invoke the button'smouse-actionproperty instead ofaction; if the button has nomouse-actionproperty, useactionas normal.
Return
tif button has button-type type, or one of type's subtypes.
Return the button at position pos in the current buffer, or
nil. If the button at pos is a text property button, the return value is a marker pointing to pos.
Return
tif button-type type is a subtype of supertype.
These are commands and functions for locating and operating on buttons in an Emacs buffer.
push-button is the command that a user uses to actually push
a button, and is bound by default in the button itself to <RET>
and to <mouse-2> using a local keymap in the button's overlay or
text properties. Commands that are useful outside the buttons itself,
such as forward-button and backward-button are
additionally available in the keymap stored in
button-buffer-map; a mode which uses buttons may want to use
button-buffer-map as a parent keymap for its keymap.
If the button has a non-nil follow-link property, and
mouse-1-click-follows-link is set, a quick <mouse-1> click
will also activate the push-button command.
See Clickable Text.
Perform the action specified by a button at location pos. pos may be either a buffer position or a mouse-event. If use-mouse-action is non-
nil, or pos is a mouse-event (see Mouse Events), try to invoke the button'smouse-actionproperty instead ofaction; if the button has nomouse-actionproperty, useactionas normal. pos defaults to point, except whenpush-buttonis invoked interactively as the result of a mouse-event, in which case, the mouse event's position is used. If there's no button at pos, do nothing and returnnil, otherwise returnt.
Move to the nth next button, or nth previous button if n is negative. If n is zero, move to the start of any button at point. If wrap is non-
nil, moving past either end of the buffer continues from the other end. If display-message is non-nil, the button's help-echo string is displayed. Any button with a non-nilskipproperty is skipped over. Returns the button found.
Move to the nth previous button, or nth next button if n is negative. If n is zero, move to the start of any button at point. If wrap is non-
nil, moving past either end of the buffer continues from the other end. If display-message is non-nil, the button's help-echo string is displayed. Any button with a non-nilskipproperty is skipped over. Returns the button found.
Return the next button after (for
next-button) or before (forprevious-button) position pos in the current buffer. If count-current is non-nil, count any button at pos in the search, instead of starting at the next button.
The Ewoc package constructs buffer text that represents a structure of Lisp objects, and updates the text to follow changes in that structure. This is like the “view” component in the “model–view–controller” design paradigm. Ewoc means “Emacs's Widget for Object Collections”.
An ewoc is a structure that organizes information required to construct buffer text that represents certain Lisp data. The buffer text of the ewoc has three parts, in order: first, fixed header text; next, textual descriptions of a series of data elements (Lisp objects that you specify); and last, fixed footer text. Specifically, an ewoc contains information on:
Typically, you define an ewoc with ewoc-create, and then pass
the resulting ewoc structure to other functions in the Ewoc package to
build nodes within it, and display it in the buffer. Once it is
displayed in the buffer, other functions determine the correspondence
between buffer positions and nodes, move point from one node's textual
representation to another, and so forth. See Abstract Display Functions.
A node encapsulates a data element much the way a variable holds a value. Normally, encapsulation occurs as a part of adding a node to the ewoc. You can retrieve the data element value and place a new value in its place, like so:
(ewoc-data node)
=> value
(ewoc-set-data node new-value)
=> new-value
You can also use, as the data element value, a Lisp object (list or vector) that is a container for the real value, or an index into some other structure. The example (see Abstract Display Example) uses the latter approach.
When the data changes, you will want to update the text in the
buffer. You can update all nodes by calling ewoc-refresh, or
just specific nodes using ewoc-invalidate, or all nodes
satisfying a predicate using ewoc-map. Alternatively, you can
delete invalid nodes using ewoc-delete or ewoc-filter,
and add new nodes in their place. Deleting a node from an ewoc deletes
its associated textual description from buffer, as well.
In this subsection, ewoc and node stand for the structures described above (see Abstract Display), while data stands for an arbitrary Lisp object used as a data element.
This constructs and returns a new ewoc, with no nodes (and thus no data elements). pretty-printer should be a function that takes one argument, a data element of the sort you plan to use in this ewoc, and inserts its textual description at point using
insert(and neverinsert-before-markers, because that would interfere with the Ewoc package's internal mechanisms).Normally, a newline is automatically inserted after the header, the footer and every node's textual description. If nosep is non-
nil, no newline is inserted. This may be useful for displaying an entire ewoc on a single line, for example, or for making nodes invisible by arranging for pretty-printer to do nothing for those nodes.An ewoc maintains its text in the buffer that is current when you create it, so switch to the intended buffer before calling
ewoc-create.
This returns a cons cell
(header.footer)made from ewoc's header and footer.
This sets the header and footer of ewoc to the strings header and footer, respectively.
These add a new node encapsulating data, putting it, respectively, at the beginning or end of ewoc's chain of nodes.
These add a new node encapsulating data, adding it to ewoc before or after node, respectively.
These return, respectively, the previous node and the next node of node in ewoc.
This returns the node in ewoc found at zero-based index n. A negative n means count from the end.
ewoc-nthreturnsnilif n is out of range.
This determines the node in ewoc which contains point (or pos if specified), and returns that node. If ewoc has no nodes, it returns
nil. If pos is before the first node, it returns the first node; if pos is after the last node, it returns the last node. The optional third arg guess should be a node that is likely to be near pos; this doesn't alter the result, but makes the function run faster.
These move point to the previous or next, respectively, argth node in ewoc.
ewoc-goto-prevdoes not move if it is already at the first node or if ewoc is empty, whereasewoc-goto-nextmoves past the last node, returningnil. Excepting this special case, these functions return the node moved to.
This function regenerates the text of ewoc. It works by deleting the text between the header and the footer, i.e., all the data elements' representations, and then calling the pretty-printer function for each node, one by one, in order.
This is similar to
ewoc-refresh, except that only nodes in ewoc are updated instead of the entire set.
This calls predicate for each data element in ewoc and deletes those nodes for which predicate returns
nil. Any args are passed to predicate.
This calls predicate for each data element in ewoc and returns a list of those elements for which predicate returns non-
nil. The elements in the list are ordered as in the buffer. Any args are passed to predicate.
This calls map-function for each data element in ewoc and updates those nodes for which map-function returns non-
nil. Any args are passed to map-function.
Here is a simple example using functions of the ewoc package to implement a color components display, an area in a buffer that represents a vector of three integers (itself representing a 24-bit RGB value) in various ways.
(setq colorcomp-ewoc nil
colorcomp-data nil
colorcomp-mode-map nil
colorcomp-labels ["Red" "Green" "Blue"])
(defun colorcomp-pp (data)
(if data
(let ((comp (aref colorcomp-data data)))
(insert (aref colorcomp-labels data) "\t: #x"
(format "%02X" comp) " "
(make-string (ash comp -2) ?#) "\n"))
(let ((cstr (format "#%02X%02X%02X"
(aref colorcomp-data 0)
(aref colorcomp-data 1)
(aref colorcomp-data 2)))
(samp " (sample text) "))
(insert "Color\t: "
(propertize samp 'face
`(foreground-color . ,cstr))
(propertize samp 'face
`(background-color . ,cstr))
"\n"))))
(defun colorcomp (color)
"Allow fiddling with COLOR in a new buffer.
The buffer is in Color Components mode."
(interactive "sColor (name or #RGB or #RRGGBB): ")
(when (string= "" color)
(setq color "green"))
(unless (color-values color)
(error "No such color: %S" color))
(switch-to-buffer
(generate-new-buffer (format "originally: %s" color)))
(kill-all-local-variables)
(setq major-mode 'colorcomp-mode
mode-name "Color Components")
(use-local-map colorcomp-mode-map)
(erase-buffer)
(buffer-disable-undo)
(let ((data (apply 'vector (mapcar (lambda (n) (ash n -8))
(color-values color))))
(ewoc (ewoc-create 'colorcomp-pp
"\nColor Components\n\n"
(substitute-command-keys
"\n\\{colorcomp-mode-map}"))))
(set (make-local-variable 'colorcomp-data) data)
(set (make-local-variable 'colorcomp-ewoc) ewoc)
(ewoc-enter-last ewoc 0)
(ewoc-enter-last ewoc 1)
(ewoc-enter-last ewoc 2)
(ewoc-enter-last ewoc nil)))
This example can be extended to be a color selection widget (in
other words, the “controller” part of the “model–view–controller”
design paradigm) by defining commands to modify colorcomp-data
and to finish the selection process, and a keymap to tie it all
together conveniently.
(defun colorcomp-mod (index limit delta)
(let ((cur (aref colorcomp-data index)))
(unless (= limit cur)
(aset colorcomp-data index (+ cur delta)))
(ewoc-invalidate
colorcomp-ewoc
(ewoc-nth colorcomp-ewoc index)
(ewoc-nth colorcomp-ewoc -1))))
(defun colorcomp-R-more () (interactive) (colorcomp-mod 0 255 1))
(defun colorcomp-G-more () (interactive) (colorcomp-mod 1 255 1))
(defun colorcomp-B-more () (interactive) (colorcomp-mod 2 255 1))
(defun colorcomp-R-less () (interactive) (colorcomp-mod 0 0 -1))
(defun colorcomp-G-less () (interactive) (colorcomp-mod 1 0 -1))
(defun colorcomp-B-less () (interactive) (colorcomp-mod 2 0 -1))
(defun colorcomp-copy-as-kill-and-exit ()
"Copy the color components into the kill ring and kill the buffer.
The string is formatted #RRGGBB (hash followed by six hex digits)."
(interactive)
(kill-new (format "#%02X%02X%02X"
(aref colorcomp-data 0)
(aref colorcomp-data 1)
(aref colorcomp-data 2)))
(kill-buffer nil))
(setq colorcomp-mode-map
(let ((m (make-sparse-keymap)))
(suppress-keymap m)
(define-key m "i" 'colorcomp-R-less)
(define-key m "o" 'colorcomp-R-more)
(define-key m "k" 'colorcomp-G-less)
(define-key m "l" 'colorcomp-G-more)
(define-key m "," 'colorcomp-B-less)
(define-key m "." 'colorcomp-B-more)
(define-key m " " 'colorcomp-copy-as-kill-and-exit)
m))
Note that we never modify the data in each node, which is fixed when the
ewoc is created to be either nil or an index into the vector
colorcomp-data, the actual color components.
This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis.
The value of this variable should be a function (of no arguments) to be called whenever a character with close parenthesis syntax is inserted. The value of
blink-paren-functionmay benil, in which case nothing is done.
This variable specifies the maximum distance to scan for a matching parenthesis before giving up.
This variable specifies the number of seconds to keep indicating the matching parenthesis. A fraction of a second often gives good results, but the default is 1, which works on all systems.
This function is the default value of
blink-paren-function. It assumes that point follows a character with close parenthesis syntax and applies the appropriate effect momentarily to the matching opening character. If that character is not already on the screen, it displays the character's context in the echo area. To avoid long delays, this function does not search farther thanblink-matching-paren-distancecharacters.Here is an example of calling this function explicitly.
(defun interactive-blink-matching-open () "Indicate momentarily the start of parenthesized sexp before point." (interactive) (let ((blink-matching-paren-distance (buffer-size)) (blink-matching-paren t)) (blink-matching-open)))
This section describes how characters are actually displayed by Emacs. Typically, a character is displayed as a glyph (a graphical symbol which occupies one character position on the screen), whose appearance corresponds to the character itself. For example, the character `a' (character code 97) is displayed as `a'. Some characters, however, are displayed specially. For example, the formfeed character (character code 12) is usually displayed as a sequence of two glyphs, `^L', while the newline character (character code 10) starts a new screen line.
You can modify how each character is displayed by defining a display table, which maps each character code into a sequence of glyphs. See Display Tables.
Here are the conventions for displaying each character code (in the absence of a display table, which can override these conventions; see Display Tables).
tab-width controls the number of
spaces per tab stop (see below).
ctl-arrow. If this variable is non-nil (the default),
these characters are displayed as sequences of two glyphs, where the
first glyph is `^' (a display table can specify a glyph to use
instead of `^'); e.g., the <DEL> character is displayed as
`^?'.
If ctl-arrow is nil, these characters are displayed as
octal escapes (see below).
This rule also applies to carriage return (character code 13), if that character appears in the buffer. But carriage returns usually do not appear in buffer text; they are eliminated as part of end-of-line conversion (see Coding System Basics).
The above display conventions apply even when there is a display
table, for any character whose entry in the active display table is
nil. Thus, when you set up a display table, you need only
specify the characters for which you want special behavior.
The following variables affect how certain characters are displayed
on the screen. Since they change the number of columns the characters
occupy, they also affect the indentation functions. They also affect
how the mode line is displayed; if you want to force redisplay of the
mode line using the new values, call the function
force-mode-line-update (see Mode Line Format).
This buffer-local variable controls how control characters are displayed. If it is non-
nil, they are displayed as a caret followed by the character: `^A'. If it isnil, they are displayed as octal escapes: a backslash followed by three octal digits, as in `\001'.
The value of this buffer-local variable is the spacing between tab stops used for displaying tab characters in Emacs buffers. The value is in units of columns, and the default is 8. Note that this feature is completely independent of the user-settable tab stops used by the command
tab-to-tab-stop. See Indent Tabs.
A display table is a special-purpose char-table
(see Char-Tables), with display-table as its subtype, which
is used to override the usual character display conventions. This
section describes how to make, inspect, and assign elements to a
display table object.
This creates and returns a display table. The table initially has
nilin all elements.
The ordinary elements of the display table are indexed by character
codes; the element at index c says how to display the character
code c. The value should be nil (which means to display
the character c according to the usual display conventions;
see Usual Display), or a vector of glyph codes (which means to
display the character c as those glyphs; see Glyphs).
Warning: if you use the display table to change the display of newline characters, the whole buffer will be displayed as one long line.
The display table also has six extra slots which serve special
purposes. Here is a table of their meanings; nil in any slot
means to use the default for that slot, as stated below.
For example, here is how to construct a display table that mimics
the effect of setting ctl-arrow to a non-nil value
(see Glyphs, for the function make-glyph-code):
(setq disptab (make-display-table))
(dotimes (i 32)
(or (= i ?\t)
(= i ?\n)
(aset disptab i
(vector (make-glyph-code ?^ 'escape-glyph)
(make-glyph-code (+ i 64) 'escape-glyph)))))
(aset disptab 127
(vector (make-glyph-code ?^ 'escape-glyph)
(make-glyph-code ?? 'escape-glyph)))))
This function returns the value of the extra slot slot of display-table. The argument slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols are
truncation,wrap,escape,control,selective-display, andvertical-border.
This function stores value in the extra slot slot of display-table. The argument slot may be a number from 0 to 5 inclusive, or a slot name (symbol). Valid symbols are
truncation,wrap,escape,control,selective-display, andvertical-border.
This function displays a description of the display table display-table in a help buffer.
This command displays a description of the current display table in a help buffer.
Each window can specify a display table, and so can each buffer.
The window's display table, if there is one, takes precedence over the
buffer's display table. If neither exists, Emacs tries to use the
standard display table; if that is nil, Emacs uses the usual
character display conventions (see Usual Display).
Note that display tables affect how the mode line is displayed, so
if you want to force redisplay of the mode line using a new display
table, call force-mode-line-update (see Mode Line Format).
This function returns window's display table, or
nilif there is none. The default for window is the selected window.
This function sets the display table of window to table. The argument table should be either a display table or
nil.
This variable is automatically buffer-local in all buffers; its value specifies the buffer's display table. If it is
nil, there is no buffer display table.
The value of this variable is the standard display table, which is used when Emacs is displaying a buffer in a window with neither a window display table nor a buffer display table defined, or when Emacs is outputting text to the standard output or error streams. Although its default is typically
nil, in an interactive session if the terminal cannot display curved quotes, its default maps curved quotes to ASCII approximations. See Keys in Documentation.
The disp-table library defines several functions for changing the standard display table.
A glyph is a graphical symbol which occupies a single character position on the screen. Each glyph is represented in Lisp as a glyph code, which specifies a character and optionally a face to display it in (see Faces). The main use of glyph codes is as the entries of display tables (see Display Tables). The following functions are used to manipulate glyph codes:
This function returns a glyph code representing char char with face face. If face is omitted or
nil, the glyph uses the default face; in that case, the glyph code is an integer. If face is non-nil, the glyph code is not necessarily an integer object.
This function returns face of glyph code glyph, or
nilif glyph uses the default face.
You can set up a glyph table to change how glyph codes are
actually displayed on text terminals. This feature is semi-obsolete;
use glyphless-char-display instead (see Glyphless Chars).
The value of this variable, if non-
nil, is the current glyph table. It takes effect only on character terminals; on graphical displays, all glyphs are displayed literally. The glyph table should be a vector whose gth element specifies how to display glyph code g, where g is the glyph code for a glyph whose face is unspecified. Each element should be one of the following:
nil- Display this glyph literally.
- a string
- Display this glyph by sending the specified string to the terminal.
- a glyph code
- Display the specified glyph code instead.
Any integer glyph code greater than or equal to the length of the glyph table is displayed literally.
Glyphless characters are characters which are displayed in a special way, e.g., as a box containing a hexadecimal code, instead of being displayed literally. These include characters which are explicitly defined to be glyphless, as well as characters for which there is no available font (on a graphical display), and characters which cannot be encoded by the terminal's coding system (on a text terminal).
The value of this variable is a char-table which defines glyphless characters and how they are displayed. Each entry must be one of the following display methods:
nil- Display the character in the usual way.
zero-width- Don't display the character.
thin-space- Display a thin space, 1-pixel wide on graphical displays, or 1-character wide on text terminals.
empty-box- Display an empty box.
hex-code- Display a box containing the Unicode codepoint of the character, in hexadecimal notation.
- an ASCII string
- Display a box containing that string. The string should contain at most 6 ASCII characters.
- a cons cell
(graphical.text)- Display with graphical on graphical displays, and with text on text terminals. Both graphical and text must be one of the display methods described above.
The
thin-space,empty-box,hex-code, and ASCII string display methods are drawn with theglyphless-charface. On text terminals, a box is emulated by square brackets, `[]'.The char-table has one extra slot, which determines how to display any character that cannot be displayed with any available font, or cannot be encoded by the terminal's coding system. Its value should be one of the above display methods, except
zero-widthor a cons cell.If a character has a non-
nilentry in an active display table, the display table takes effect; in this case, Emacs does not consultglyphless-char-displayat all.
This user option provides a convenient way to set
glyphless-char-displayfor groups of similar characters. Do not set its value directly from Lisp code; the value takes effect only via a custom:setfunction (see Variable Definitions), which updatesglyphless-char-display.Its value should be an alist of elements
(group.method), where group is a symbol specifying a group of characters, and method is a symbol specifying how to display them.group should be one of the following:
c0-control- ASCII control characters
U+0000toU+001F, excluding the newline and tab characters (normally displayed as escape sequences like `^A'; see How Text Is Displayed).
c1-control- Non-ASCII, non-printing characters
U+0080toU+009F(normally displayed as octal escape sequences like `\230').
format-control- Characters of Unicode General Category [Cf], such as `U+200E' (Left-to-Right Mark), but excluding characters that have graphic images, such as `U+00AD' (Soft Hyphen).
no-font- Characters for there is no suitable font, or which cannot be encoded by the terminal's coding system.
The method symbol should be one of
zero-width,thin-space,empty-box, orhex-code. These have the same meanings as inglyphless-char-display, above.
This section describes how to make Emacs ring the bell (or blink the screen) to attract the user's attention. Be conservative about how often you do this; frequent bells can become irritating. Also be careful not to use just beeping when signaling an error is more appropriate (see Errors).
This function beeps, or flashes the screen (see
visible-bellbelow). It also terminates any keyboard macro currently executing unless do-not-terminate is non-nil.
This variable determines whether Emacs should flash the screen to represent a bell. Non-
nilmeans yes,nilmeans no. This is effective on graphical displays, and on text terminals provided the terminal's Termcap entry defines the visible bell capability (`vb').
If this is non-
nil, it specifies how Emacs should ring the bell. Its value should be a function of no arguments. If this is non-nil, it takes precedence over thevisible-bellvariable.
Emacs works with several window systems, most notably the X Window System. Both Emacs and X use the term “window”, but use it differently. An Emacs frame is a single window as far as X is concerned; the individual Emacs windows are not known to X at all.
This terminal-local variable tells Lisp programs what window system Emacs is using for displaying the frame. The possible values are
x- Emacs is displaying the frame using X.
w32- Emacs is displaying the frame using native MS-Windows GUI.
ns- Emacs is displaying the frame using the Nextstep interface (used on GNUstep and Mac OS X).
pc- Emacs is displaying the frame using MS-DOS direct screen writes.
nil- Emacs is displaying the frame on a character-based terminal.
This variable holds the value of
window-systemused for the first frame created by Emacs during startup. (When Emacs is invoked with the --daemon option, it does not create any initial frames, soinitial-window-systemisnil, except on MS-Windows, where it is stillw32. See daemon.)
This function returns a symbol whose name tells what window system is used for displaying frame (which defaults to the currently selected frame). The list of possible symbols it returns is the same one documented for the variable
window-systemabove.
Do not use window-system and
initial-window-system as predicates or boolean flag variables,
if you want to write code that works differently on text terminals and
graphic displays. That is because window-system is not a good
indicator of Emacs capabilities on a given display type. Instead, use
display-graphic-p or any of the other display-*-p
predicates described in Display Feature Testing.
Tooltips are special frames (see Frames) that are used to display helpful hints (a.k.a. “tips”) related to the current position of the mouse pointer. Emacs uses tooltips to display help strings about active portions of text (see Special Properties) and about various UI elements, such as menu items (see Extended Menu Items) and tool-bar buttons (see Tool Bar).
Tooltip Mode is a minor mode that enables display of tooltips. Turning off this mode causes the tooltips be displayed in the echo area. On text-mode (a.k.a. “TTY”) frames, tooltips are always displayed in the echo area.
When Emacs is built with GTK+ support, it by default displays tooltips
using GTK+ functions, and the appearance of the tooltips is then
controlled by GTK+ settings. GTK+ tooltips can be disabled by
changing the value of the variable x-gtk-use-system-tooltips to
nil. The rest of this subsection describes how to control
non-GTK+ tooltips, which are presented by Emacs itself.
Since tooltips are special frames, they have their frame parameters (see Frame Parameters). Unlike other frames, the frame parameters for tooltips are stored in a special variable.
This customizable option holds the frame parameters used for displaying tooltips. Any font and color parameters are ignored, and the corresponding attributes of the
tooltipface are used instead. Ifleftortopparameters are included, they are used as absolute frame-relative coordinates where the tooltip should be shown. (Mouse-relative position of the tooltip can be customized using the variables described in Tooltips.) Note that theleftandtopparameters, if present, override the values of mouse-relative offsets.
The tooltip face determines the appearance of text shown in
tooltips. It should generally use a variable-pitch font of size that
is preferably smaller than the default frame font.
This abnormal hook is a list of functions to call when Emacs needs to display a tooltip. Each function is called with a single argument event which is a copy of the last mouse movement event. If a function on this list actually displays the tooltip, it should return non-
nil, and then the rest of the functions will not be called. The default value of this variable is a single functiontooltip-help-tips.
If you write your own function to be put on the
tooltip-functions list, you may need to know the buffer of the
mouse event that triggered the tooltip display. The following
function provides that information.
This function returns the buffer over which event occurred. Call it with the argument of the function from
tooltip-functionsto obtain the buffer whose text triggered the tooltip. Note that the event might occur not over a buffer (e.g., over the tool bar), in which case this function will returnnil.
Other aspects of tooltip display are controlled by several customizable settings; see Tooltips.
Emacs can display text written in scripts, such as Arabic, Farsi, and Hebrew, whose natural ordering for horizontal text display runs from right to left. Furthermore, segments of Latin script and digits embedded in right-to-left text are displayed left-to-right, while segments of right-to-left script embedded in left-to-right text (e.g., Arabic or Hebrew text in comments or strings in a program source file) are appropriately displayed right-to-left. We call such mixtures of left-to-right and right-to-left text bidirectional text. This section describes the facilities and options for editing and displaying bidirectional text.
Text is stored in Emacs buffers and strings in logical (or reading) order, i.e., the order in which a human would read each character. In right-to-left and bidirectional text, the order in which characters are displayed on the screen (called visual order) is not the same as logical order; the characters' screen positions do not increase monotonically with string or buffer position. In performing this bidirectional reordering, Emacs follows the Unicode Bidirectional Algorithm (a.k.a. UBA), which is described in Annex #9 of the Unicode standard (http://www.unicode.org/reports/tr9/). Emacs provides a “Full Bidirectionality” class implementation of the UBA, consistent with the requirements of the Unicode Standard v8.0.
If the value of this buffer-local variable is non-
nil(the default), Emacs performs bidirectional reordering for display. The reordering affects buffer text, as well as display strings and overlay strings from text and overlay properties in the buffer (see Overlay Properties, and see Display Property). If the value isnil, Emacs does not perform bidirectional reordering in the buffer.The default value of
bidi-display-reorderingcontrols the reordering of strings which are not directly supplied by a buffer, including the text displayed in mode lines (see Mode Line Format) and header lines (see Header Lines).
Emacs never reorders the text of a unibyte buffer, even if
bidi-display-reordering is non-nil in the buffer. This
is because unibyte buffers contain raw bytes, not characters, and thus
lack the directionality properties required for reordering.
Therefore, to test whether text in a buffer will be reordered for
display, it is not enough to test the value of
bidi-display-reordering alone. The correct test is this:
(if (and enable-multibyte-characters
bidi-display-reordering)
;; Buffer is being reordered for display
)
However, unibyte display and overlay strings are reordered if their parent buffer is reordered. This is because plain-ascii strings are stored by Emacs as unibyte strings. If a unibyte display or overlay string includes non-ascii characters, these characters are assumed to have left-to-right direction.
Text covered by display text properties, by overlays with
display properties whose value is a string, and by any other
properties that replace buffer text, is treated as a single unit when
it is reordered for display. That is, the entire chunk of text
covered by these properties is reordered together. Moreover, the
bidirectional properties of the characters in such a chunk of text are
ignored, and Emacs reorders them as if they were replaced with a
single character U+FFFC, known as the Object Replacement
Character. This means that placing a display property over a portion
of text may change the way that the surrounding text is reordered for
display. To prevent this unexpected effect, always place such
properties on text whose directionality is identical with text that
surrounds it.
Each paragraph of bidirectional text has a base direction, either right-to-left or left-to-right. Left-to-right paragraphs are displayed beginning at the left margin of the window, and are truncated or continued when the text reaches the right margin. Right-to-left paragraphs are displayed beginning at the right margin, and are continued or truncated at the left margin.
By default, Emacs determines the base direction of each paragraph by looking at the text at its beginning. The precise method of determining the base direction is specified by the UBA; in a nutshell, the first character in a paragraph that has an explicit directionality determines the base direction of the paragraph. However, sometimes a buffer may need to force a certain base direction for its paragraphs. For example, buffers containing program source code should force all paragraphs to be displayed left-to-right. You can use following variable to do this:
If the value of this buffer-local variable is the symbol
right-to-leftorleft-to-right, all paragraphs in the buffer are assumed to have that specified direction. Any other value is equivalent tonil(the default), which means to determine the base direction of each paragraph from its contents.Modes for program source code should set this to
left-to-right. Prog mode does this by default, so modes derived from Prog mode do not need to set this explicitly (see Basic Major Modes).
This function returns the paragraph direction at point in the named buffer. The returned value is a symbol, either
left-to-rightorright-to-left. If buffer is omitted ornil, it defaults to the current buffer. If the buffer-local value of the variablebidi-paragraph-directionis non-nil, the returned value will be identical to that value; otherwise, the returned value reflects the paragraph direction determined dynamically by Emacs. For buffers whose value ofbidi-display-reorderingisnilas well as unibyte buffers, this function always returnsleft-to-right.
Sometimes there's a need to move point in strict visual order, either to the left or to the right of its current screen position. Emacs provides a primitive to do that.
This function moves point of the currently selected window to the buffer position that appears immediately to the right or to the left of point on the screen. If direction is positive, point will move one screen position to the right, otherwise it will move one screen position to the left. Note that, depending on the surrounding bidirectional context, this could potentially move point many buffer positions away. If invoked at the end of a screen line, the function moves point to the rightmost or leftmost screen position of the next or previous screen line, as appropriate for the value of direction.
The function returns the new buffer position as its value.
Bidirectional reordering can have surprising and unpleasant effects when two strings with bidirectional content are juxtaposed in a buffer, or otherwise programmatically concatenated into a string of text. A typical problematic case is when a buffer consists of sequences of text fields separated by whitespace or punctuation characters, like Buffer Menu mode or Rmail Summary Mode. Because the punctuation characters used as separators have weak directionality, they take on the directionality of surrounding text. As result, a numeric field that follows a field with bidirectional content can be displayed to the left of the preceding field, messing up the expected layout. There are several ways to avoid this problem:
U+200E, LEFT-TO-RIGHT MARK, or
LRM, to the end of each field that may have bidirectional
content, or prepend it to the beginning of the following field. The
function bidi-string-mark-left-to-right, described below, comes
in handy for this purpose. (In a right-to-left paragraph, use
U+200F, RIGHT-TO-LEFT MARK, or RLM, instead.) This
is one of the solutions recommended by the UBA.
display property or overlay with a
property value of the form (space . PROPS) (see Specified Space). Emacs treats this display specification as a paragraph
separator, and reorders the text on either side separately.
This function returns its argument string, possibly modified, such that the result can be safely concatenated with another string, or juxtaposed with another string in a buffer, without disrupting the relative layout of this string and the next one on display. If the string returned by this function is displayed as part of a left-to-right paragraph, it will always appear on display to the left of the text that follows it. The function works by examining the characters of its argument, and if any of those characters could cause reordering on display, the function appends the LRM character to the string. The appended LRM character is made invisible by giving it an
invisibletext property oft(see Invisible Text).
The reordering algorithm uses the bidirectional properties of the
characters stored as their bidi-class property
(see Character Properties). Lisp programs can change these
properties by calling the put-char-code-property function.
However, doing this requires a thorough understanding of the
UBA, and is therefore not recommended. Any changes to the
bidirectional properties of a character have global effect: they
affect all Emacs frames and windows.
Similarly, the mirroring property is used to display the
appropriate mirrored character in the reordered text. Lisp programs
can affect the mirrored display by changing this property. Again, any
such changes affect all of Emacs display.
The bidirectional properties of characters can be overridden by inserting into the text special directional control characters, LEFT-TO-RIGHT OVERRIDE (LRO) and RIGHT-TO-LEFT OVERRIDE (RLO). Any characters between a RLO and the following newline or POP DIRECTIONAL FORMATTING (PDF) control character, whichever comes first, will be displayed as if they were strong right-to-left characters, i.e. they will be reversed on display. Similarly, any characters between LRO and PDF or newline will display as if they were strong left-to-right, and will not be reversed even if they are strong right-to-left characters.
These overrides are useful when you want to make some text unaffected by the reordering algorithm, and instead directly control the display order. But they can also be used for malicious purposes, known as phishing. Specifically, a URL on a Web page or a link in an email message can be manipulated to make its visual appearance unrecognizable, or similar to some popular benign location, while the real location, interpreted by a browser in the logical order, is very different.
Emacs provides a primitive that applications can use to detect instances of text whose bidirectional properties were overridden so as to make a left-to-right character display as if it were a right-to-left character, or vise versa.
This function looks at the text of the specified object between positions from (inclusive) and to (exclusive), and returns the first position where it finds a strong left-to-right character whose directional properties were forced to display the character as right-to-left, or for a strong right-to-left character that was forced to display as left-to-right. If it finds no such characters in the specified region of text, it returns
nil.The optional argument object specifies which text to search, and defaults to the current buffer. If object is non-
nil, it can be some other buffer, or it can be a string or a window. If it is a string, the function searches that string. If it is a window, the function searches the buffer displayed in that window. If a buffer whose text you want to examine is displayed in some window, we recommend to specify it by that window, rather than pass the buffer to the function. This is because telling the function about the window allows it to correctly account for window-specific overlays, which might change the result of the function if some text in the buffer is covered by overlays.
When text that includes mixed right-to-left and left-to-right characters and bidirectional controls is copied into a different location, it can change its visual appearance, and also can affect the visual appearance of the surrounding text at destination. This is because reordering of bidirectional text specified by the UBA has non-trivial context-dependent effects both on the copied text and on the text at copy destination that will surround it.
Sometimes, a Lisp program may need to preserve the exact visual appearance of the copied text at destination, and of the text that surrounds the copy. Lisp programs can use the following function to achieve that effect.
This function works similar to
buffer-substring(see Buffer Contents), but it prepends and appends to the copied text bidi directional control characters necessary to preserve the visual appearance of the text when it is inserted at another place. Optional argument no-properties, if non-nil, means remove the text properties from the copy of the text.
This chapter is about starting and getting out of Emacs, access to values in the operating system environment, and terminal input, output.
See Building Emacs, for related information. See Display, for additional operating system status information pertaining to the terminal and the screen.
This section describes what Emacs does when it is started, and how you can customize these actions.
When Emacs is started up, it performs the following operations
(see normal-top-level in startup.el):
load-path, by running the file named
subdirs.el in each directory in the list. Normally, this file
adds the directory's subdirectories to the list, and those are scanned
in their turn. The files subdirs.el are normally generated
automatically when Emacs is installed.
load-path
directories. This file is intended for registering input methods.
The search is only for any personal leim-list.el files that you
may have created; it skips the directories containing the standard Emacs
libraries (these should contain only a single leim-list.el file,
which is compiled into the Emacs executable).
before-init-time to the value of
current-time (see Time of Day). It also sets
after-init-time to nil, which signals to Lisp programs
that Emacs is being initialized.
initial-window-system specifies (see initial-window-system). The initialization function for
each supported window system is specified by
window-system-initialization-alist. If the value
of initial-window-system is windowsystem, then the
appropriate initialization function is defined in the file
term/windowsystem-win.el. This file should have been
compiled into the Emacs executable when it was built.
before-init-hook.
custom-reevaluate-setting to re-initialize the members
of the list custom-delayed-init-variables. These are any
pre-loaded user options whose default value depends on the run-time,
rather than build-time, context.
See custom-initialize-delay.
inhibit-default-init is non-nil, nor if the options
`-q', `-Q', or `--batch' were specified.
abbrev-file-name, if that file exists and can be read
(see abbrev-file-name). This is not done if the
option `--batch' was specified.
package-enable-at-startup is non-nil, it calls the
function package-initialize to activate any optional Emacs Lisp
package that has been installed. See Packaging Basics.
after-init-time to the value of
current-time. This variable was set to nil earlier;
setting it to the current time signals that the initialization phase
is over, and, together with before-init-time, provides the
measurement of how long it took.
after-init-hook.
initial-major-mode.
tty-setup-hook. This is not done
in --batch mode, nor if term-file-prefix is nil.
inhibit-startup-echo-area-message.
--batch was specified.
(substitute-command-keys initial-scratch-message) into that buffer.
initial-buffer-choice is a string, it visits the file (or
directory) with that name. If it is a function, it calls the function
with no arguments and selects the buffer that it returns. If one file
is given as a command line argument, that file is visited and its
buffer displayed alongside initial-buffer-choice. If more than
one file is given, all of the files are visited and the *Buffer
List* buffer is displayed alongside initial-buffer-choice.
emacs-startup-hook.
frame-notice-user-settings, which modifies the
parameters of the selected frame according to whatever the init files
specify.
window-setup-hook. The only difference between this
hook and emacs-startup-hook is that this one runs after the
previously mentioned modifications to the frame parameters.
inhibit-startup-screen or initial-buffer-choice
are non-nil, or if the `--no-splash' or `-Q' command-line
options were specified.
--daemon was specified, it calls
server-start, and on Posix systems also detaches from the
controlling terminal. See Emacs Server.
emacs-session-restore passing it as argument the ID of the
previous session. See Session Management.
The following options affect some aspects of the startup sequence.
This variable, if non-
nil, inhibits the startup screen. In that case, Emacs typically displays the *scratch* buffer; but seeinitial-buffer-choice, below.Do not set this variable in the init file of a new user, or in a way that affects more than one user, as that would prevent new users from receiving information about copyleft and basic Emacs usage.
inhibit-startup-messageandinhibit-splash-screenare aliases for this variable.
If non-
nil, this variable is a string that specifies a file or directory for Emacs to display after starting up, instead of the startup screen. If its value is a function, Emacs calls that function which must return a buffer which is then displayed. If its value ist, Emacs displays the *scratch* buffer.
This variable controls the display of the startup echo area message. You can suppress the startup echo area message by adding text with this form to your init file:
(setq inhibit-startup-echo-area-message "your-login-name")Emacs explicitly checks for an expression as shown above in your init file; your login name must appear in the expression as a Lisp string constant. You can also use the Customize interface. Other methods of setting
inhibit-startup-echo-area-messageto the same value do not inhibit the startup message. This way, you can easily inhibit the message for yourself if you wish, but thoughtless copying of your init file will not inhibit the message for someone else.
This variable, if non-
nil, should be a string, which is treated as documentation to be inserted into the *scratch* buffer when Emacs starts up. If it isnil, the *scratch* buffer is empty.
The following command-line options affect some aspects of the startup sequence. See Initial Options.
--no-splash--batch--daemon--no-init-file-q--no-site-file--quick-QWhen you start Emacs, it normally attempts to load your init file. This is either a file named .emacs or .emacs.el in your home directory, or a file named init.el in a subdirectory named .emacs.d in your home directory.
The command-line switches `-q', `-Q', and `-u' control whether and where to find the init file; `-q' (and the stronger `-Q') says not to load an init file, while `-u user' says to load user's init file instead of yours. See Entering Emacs. If neither option is specified, Emacs uses the LOGNAME environment variable, or the USER (most systems) or USERNAME (MS systems) variable, to find your home directory and thus your init file; this way, even if you have su'd, Emacs still loads your own init file. If those environment variables are absent, though, Emacs uses your user-id to find your home directory.
An Emacs installation may have a default init file, which is a
Lisp library named default.el. Emacs finds this file through
the standard search path for libraries (see How Programs Do Loading). The Emacs distribution does not come with this file; it is
intended for local customizations. If the default init file exists,
it is loaded whenever you start Emacs. But your own personal init
file, if any, is loaded first; if it sets inhibit-default-init
to a non-nil value, then Emacs does not subsequently load the
default.el file. In batch mode, or if you specify `-q'
(or `-Q'), Emacs loads neither your personal init file nor
the default init file.
Another file for site-customization is site-start.el. Emacs loads this before the user's init file. You can inhibit the loading of this file with the option `--no-site-file'.
This variable specifies the site-customization file to load before the user's init file. Its normal value is
"site-start". The only way you can change it with real effect is to do so before dumping Emacs.
See Init File Examples, for examples of how to make various commonly desired customizations in your .emacs file.
If this variable is non-
nil, it prevents Emacs from loading the default initialization library file. The default value isnil.
This normal hook is run, once, just before loading all the init files (site-start.el, your init file, and default.el). (The only way to change it with real effect is before dumping Emacs.)
This normal hook is run, once, just after loading all the init files (site-start.el, your init file, and default.el), before loading the terminal-specific library (if started on a text terminal) and processing the command-line action arguments.
This normal hook is run, once, just after handling the command line arguments. In batch mode, Emacs does not run this hook.
This normal hook is very similar to
emacs-startup-hook. The only difference is that it runs slightly later, after setting of the frame parameters. See window-setup-hook.
This variable holds the absolute file name of the user's init file. If the actual init file loaded is a compiled file, such as .emacs.elc, the value refers to the corresponding source file.
This variable holds the name of the .emacs.d directory. It is ~/.emacs.d on all platforms but MS-DOS.
Each terminal type can have its own Lisp library that Emacs loads when
run on that type of terminal. The library's name is constructed by
concatenating the value of the variable term-file-prefix and the
terminal type (specified by the environment variable TERM).
Normally, term-file-prefix has the value "term/";
changing this is not recommended. If there is an entry matching
TERM in the term-file-aliases association list,
Emacs uses the associated value in place of TERM.
Emacs finds the file in the normal manner, by searching the
load-path directories, and trying the `.elc' and
`.el' suffixes.
The usual role of a terminal-specific library is to enable special
keys to send sequences that Emacs can recognize. It may also need to
set or add to input-decode-map if the Termcap or Terminfo entry
does not specify all the terminal's function keys. See Terminal Input.
When the name of the terminal type contains a hyphen or underscore,
and no library is found whose name is identical to the terminal's
name, Emacs strips from the terminal's name the last hyphen or
underscore and everything that follows
it, and tries again. This process is repeated until Emacs finds a
matching library, or until there are no more hyphens or underscores in the name
(i.e., there is no terminal-specific library). For example, if the
terminal name is `xterm-256color' and there is no
term/xterm-256color.el library, Emacs tries to load
term/xterm.el. If necessary, the terminal library can evaluate
(getenv "TERM") to find the full name of the terminal type.
Your init file can prevent the loading of the terminal-specific
library by setting the variable term-file-prefix to nil.
You can also arrange to override some of the actions of the
terminal-specific library by using tty-setup-hook. This is
a normal hook that Emacs runs after initializing a new text terminal.
You could use this hook to define initializations for terminals that do not
have their own libraries. See Hooks.
If the value of this variable is non-
nil, Emacs loads a terminal-specific initialization file as follows:(load (concat term-file-prefix (getenv "TERM")))You may set the
term-file-prefixvariable tonilin your init file if you do not wish to load the terminal-initialization file.On MS-DOS, Emacs sets the TERM environment variable to `internal'.
This variable is an an association list mapping terminal types to their aliases. For example, an element of the form
("vt102" . "vt100")means to treat a terminal of type `vt102' like one of type `vt100'.
This variable is a normal hook that Emacs runs after initializing a new text terminal. (This applies when Emacs starts up in non-windowed mode, and when making a tty emacsclient connection.) The hook runs after loading your init file (if applicable) and the terminal-specific Lisp file, so you can use it to adjust the definitions made by that file.
For a related feature, see window-setup-hook.
You can use command-line arguments to request various actions when you start Emacs. Note that the recommended way of using Emacs is to start it just once, after logging in, and then do all editing in the same Emacs session (see Entering Emacs). For this reason, you might not use command-line arguments very often; nonetheless, they can be useful when invoking Emacs from session scripts or debugging Emacs. This section describes how Emacs processes command-line arguments.
This function parses the command line that Emacs was called with, processes it, and (amongst other things) loads the user's init file and displays the startup messages.
The value of this variable is
tonce the command line has been processed.If you redump Emacs by calling
dump-emacs(see Building Emacs), you may wish to set this variable tonilfirst in order to cause the new dumped Emacs to process its new command-line arguments.
This variable is an alist of user-defined command-line options and associated handler functions. By default it is empty, but you can add elements if you wish.
A command-line option is an argument on the command line, which has the form:
-optionThe elements of the
command-switch-alistlook like this:(option . handler-function)The car, option, is a string, the name of a command-line option (not including the initial hyphen). The handler-function is called to handle option, and receives the option name as its sole argument.
In some cases, the option is followed in the command line by an argument. In these cases, the handler-function can find all the remaining command-line arguments in the variable
command-line-args-left(see below). (The entire list of command-line arguments is incommand-line-args.)The command-line arguments are parsed by the
command-line-1function in the startup.el file. See also Command Line Arguments for Emacs Invocation.
The value of this variable is the list of command-line arguments passed to Emacs.
The value of this variable is the list of command-line arguments that have not yet been processed.
This variable's value is a list of functions for handling an unrecognized command-line argument. Each time the next argument to be processed has no special meaning, the functions in this list are called, in order of appearance, until one of them returns a non-
nilvalue.These functions are called with no arguments. They can access the command-line argument under consideration through the variable
argi, which is bound temporarily at this point. The remaining arguments (not including the current one) are in the variablecommand-line-args-left.When a function recognizes and processes the argument in
argi, it should return a non-nilvalue to say it has dealt with that argument. If it has also dealt with some of the following arguments, it can indicate that by deleting them fromcommand-line-args-left.If all of these functions return
nil, then the argument is treated as a file name to visit.
There are two ways to get out of Emacs: you can kill the Emacs job, which exits permanently, or you can suspend it, which permits you to reenter the Emacs process later. (In a graphical environment, you can of course simply switch to another application without doing anything special to Emacs, then switch back to Emacs when you want.)
Killing Emacs means ending the execution of the Emacs process.
If you started Emacs from a terminal, the parent process normally
resumes control. The low-level primitive for killing Emacs is
kill-emacs.
This command calls the hook
kill-emacs-hook, then exits the Emacs process and kills it.If exit-data is an integer, that is used as the exit status of the Emacs process. (This is useful primarily in batch operation; see Batch Mode.)
If exit-data is a string, its contents are stuffed into the terminal input buffer so that the shell (or whatever program next reads input) can read them.
The kill-emacs function is normally called via the
higher-level command C-x C-c
(save-buffers-kill-terminal). See Exiting. It is also called automatically if Emacs receives a
SIGTERM or SIGHUP operating system signal (e.g., when the
controlling terminal is disconnected), or if it receives a
SIGINT signal while running in batch mode (see Batch Mode).
This normal hook is run by
kill-emacs, before it kills Emacs.Because
kill-emacscan be called in situations where user interaction is impossible (e.g., when the terminal is disconnected), functions on this hook should not attempt to interact with the user. If you want to interact with the user when Emacs is shutting down, usekill-emacs-query-functions, described below.
When Emacs is killed, all the information in the Emacs process,
aside from files that have been saved, is lost. Because killing Emacs
inadvertently can lose a lot of work, the
save-buffers-kill-terminal command queries for confirmation if
you have buffers that need saving or subprocesses that are running.
It also runs the abnormal hook kill-emacs-query-functions:
When
save-buffers-kill-terminalis killing Emacs, it calls the functions in this hook, after asking the standard questions and before callingkill-emacs. The functions are called in order of appearance, with no arguments. Each function can ask for additional confirmation from the user. If any of them returnsnil,save-buffers-kill-emacsdoes not kill Emacs, and does not run the remaining functions in this hook. Callingkill-emacsdirectly does not run this hook.
On text terminals, it is possible to suspend Emacs, which
means stopping Emacs temporarily and returning control to its superior
process, which is usually the shell. This allows you to resume
editing later in the same Emacs process, with the same buffers, the
same kill ring, the same undo history, and so on. To resume Emacs,
use the appropriate command in the parent shell—most likely
fg.
Suspending works only on a terminal device from which the Emacs session was started. We call that device the controlling terminal of the session. Suspending is not allowed if the controlling terminal is a graphical terminal. Suspending is usually not relevant in graphical environments, since you can simply switch to another application without doing anything special to Emacs.
Some operating systems (those without SIGTSTP, or MS-DOS) do
not support suspension of jobs; on these systems, suspension
actually creates a new shell temporarily as a subprocess of Emacs.
Then you would exit the shell to return to Emacs.
This function stops Emacs and returns control to the superior process. If and when the superior process resumes Emacs,
suspend-emacsreturnsnilto its caller in Lisp.This function works only on the controlling terminal of the Emacs session; to relinquish control of other tty devices, use
suspend-tty(see below). If the Emacs session uses more than one terminal, you must delete the frames on all the other terminals before suspending Emacs, or this function signals an error. See Multiple Terminals.If string is non-
nil, its characters are sent to Emacs's superior shell, to be read as terminal input. The characters in string are not echoed by the superior shell; only the results appear.Before suspending,
suspend-emacsruns the normal hooksuspend-hook. After the user resumes Emacs,suspend-emacsruns the normal hooksuspend-resume-hook. See Hooks.The next redisplay after resumption will redraw the entire screen, unless the variable
no-redraw-on-reenteris non-nil. See Refresh Screen.Here is an example of how you could use these hooks:
(add-hook 'suspend-hook (lambda () (or (y-or-n-p "Really suspend? ") (error "Suspend canceled")))) (add-hook 'suspend-resume-hook (lambda () (message "Resumed!") (sit-for 2)))Here is what you would see upon evaluating
(suspend-emacs "pwd"):---------- Buffer: Minibuffer ---------- Really suspend? y ---------- Buffer: Minibuffer ---------- ---------- Parent Shell ---------- bash$ /home/username bash$ fg ---------- Echo Area ---------- Resumed!Note that `pwd' is not echoed after Emacs is suspended. But it is read and executed by the shell.
This variable is a normal hook that Emacs runs on resuming after a suspension.
If tty specifies a terminal device used by Emacs, this function relinquishes the device and restores it to its prior state. Frames that used the device continue to exist, but are not updated and Emacs doesn't read input from them. tty can be a terminal object, a frame (meaning the terminal for that frame), or
nil(meaning the terminal for the selected frame). See Multiple Terminals.If tty is already suspended, this function does nothing.
This function runs the hook
suspend-tty-functions, passing the terminal object as an argument to each function.
This function resumes the previously suspended terminal device tty; where tty has the same possible values as it does for
suspend-tty.This function reopens the terminal device, re-initializes it, and redraws it with that terminal's selected frame. It then runs the hook
resume-tty-functions, passing the terminal object as an argument to each function.If the same device is already used by another Emacs terminal, this function signals an error. If tty is not suspended, this function does nothing.
This function returns non-
nilif tty is the controlling terminal of the Emacs session; tty can be a terminal object, a frame (meaning the terminal for that frame), ornil(meaning the terminal for the selected frame).
This command suspends a frame. For GUI frames, it calls
iconify-frame(see Visibility of Frames); for frames on text terminals, it calls eithersuspend-emacsorsuspend-tty, depending on whether the frame is displayed on the controlling terminal device or not.
Emacs provides access to variables in the operating system environment through various functions. These variables include the name of the system, the user's UID, and so on.
This variable holds the standard GNU configuration name for the hardware/software configuration of your system, as a string. For example, a typical value for a 64-bit GNU/Linux system is `"x86_64-unknown-linux-gnu"'.
The value of this variable is a symbol indicating the type of operating system Emacs is running on. The possible values are:
aix- IBM's AIX.
berkeley-unix- Berkeley BSD and its variants.
cygwin- Cygwin, a Posix layer on top of MS-Windows.
darwin- Darwin (Mac OS X).
gnu- The GNU system (using the GNU kernel, which consists of the HURD and Mach).
gnu/linux- A GNU/Linux system—that is, a variant GNU system, using the Linux kernel. (These systems are the ones people often call “Linux”, but actually Linux is just the kernel, not the whole system.)
gnu/kfreebsd- A GNU (glibc-based) system with a FreeBSD kernel.
hpux- Hewlett-Packard HPUX operating system.
irix- Silicon Graphics Irix system.
nacl- Google Native Client (NaCl) sandboxing system.
ms-dos- Microsoft's DOS. Emacs compiled with DJGPP for MS-DOS binds
system-typetoms-doseven when you run it on MS-Windows.
usg-unix-v- AT&T Unix System V.
windows-nt- Microsoft Windows NT, 9X and later. The value of
system-typeis alwayswindows-nt, e.g., even on Windows 10.We do not wish to add new symbols to make finer distinctions unless it is absolutely necessary! In fact, we hope to eliminate some of these alternatives in the future. If you need to make a finer distinction than
system-typeallows for, you can testsystem-configuration, e.g., against a regexp.
This function returns the name of the machine you are running on, as a string.
If this variable is non-
nil, it is used instead ofsystem-namefor purposes of generating email addresses. For example, it is used when constructing the default value ofuser-mail-address. See User Identification. (Since this is done when Emacs starts up, the value actually used is the one saved when Emacs was dumped. See Building Emacs.)
This function returns the value of the environment variable var, as a string. var should be a string. If var is undefined in the environment,
getenvreturnsnil. It returns `""' if var is set but null. Within Emacs, a list of environment variables and their values is kept in the variableprocess-environment.(getenv "USER") => "lewis"The shell command
printenvprints all or part of the environment:bash$ printenv PATH=/usr/local/bin:/usr/bin:/bin USER=lewis TERM=xterm SHELL=/bin/bash HOME=/home/lewis ...
This command sets the value of the environment variable named variable to value. variable should be a string. Internally, Emacs Lisp can handle any string. However, normally variable should be a valid shell identifier, that is, a sequence of letters, digits and underscores, starting with a letter or underscore. Otherwise, errors may occur if subprocesses of Emacs try to access the value of variable. If value is omitted or
nil(or, interactively, with a prefix argument),setenvremoves variable from the environment. Otherwise, value should be a string.If the optional argument substitute is non-
nil, Emacs calls the functionsubstitute-env-varsto expand any environment variables in value.
setenvworks by modifyingprocess-environment; binding that variable withletis also reasonable practice.
setenvreturns the new value of variable, ornilif it removed variable from the environment.
This variable is a list of strings, each describing one environment variable. The functions
getenvandsetenvwork by means of this variable.process-environment => ("PATH=/usr/local/bin:/usr/bin:/bin" "USER=lewis" "TERM=xterm" "SHELL=/bin/bash" "HOME=/home/lewis" ...)If
process-environmentcontains multiple elements that specify the same environment variable, the first of these elements specifies the variable, and the others are ignored.
This variable holds the list of environment variables Emacs inherited from its parent process when Emacs started.
This variable holds a string that says which character separates directories in a search path (as found in an environment variable). Its value is
":"for Unix and GNU systems, and";"for MS systems.
This function takes a search path string such as the value of the PATH environment variable, and splits it at the separators, returning a list of directory names.
nilin this list means the current directory. Although the function's name says “colon”, it actually uses the value ofpath-separator.(parse-colon-path ":/foo:/bar") => (nil "/foo/" "/bar/")
This variable holds the program name under which Emacs was invoked. The value is a string, and does not include a directory name.
This variable holds the directory from which the Emacs executable was invoked, or
nilif that directory cannot be determined.
If non-
nil, this is a directory within which to look for the lib-src and etc subdirectories. In an installed Emacs, it is normallynil. It is non-nilwhen Emacs can't find those directories in their standard installed locations, but can find them in a directory related somehow to the one containing the Emacs executable (i.e.,invocation-directory).
This function returns the current 1-minute, 5-minute, and 15-minute system load averages, in a list. The load average indicates the number of processes trying to run on the system.
By default, the values are integers that are 100 times the system load averages, but if use-float is non-
nil, then they are returned as floating-point numbers without multiplying by 100.If it is impossible to obtain the load average, this function signals an error. On some platforms, access to load averages requires installing Emacs as setuid or setgid so that it can read kernel information, and that usually isn't advisable.
If the 1-minute load average is available, but the 5- or 15-minute averages are not, this function returns a shortened list containing the available averages.
(load-average) => (169 48 36) (load-average t) => (1.69 0.48 0.36)The shell command
uptimereturns similar information.
This variable holds the erase character that was selected in the system's terminal driver, before Emacs was started.
This variable says which user's init files should be used by Emacs—or
nilif none.""stands for the user who originally logged in. The value reflects command-line options such as `-q' or `-u user'.Lisp packages that load files of customizations, or any other sort of user profile, should obey this variable in deciding where to find it. They should load the profile of the user name found in this variable. If
init-file-userisnil, meaning that the `-q', `-Q', or `-batch' option was used, then Lisp packages should not load any customization files or user profile.
This holds the nominal email address of the user who is using Emacs. Emacs normally sets this variable to a default value after reading your init files, but not if you have already set it. So you can set the variable to some other value in your init file if you do not want to use the default value.
This function returns the name under which the user is logged in. It uses the environment variables LOGNAME or USER if either is set. Otherwise, the value is based on the effective UID, not the real UID.
If you specify uid (a number), the result is the user name that corresponds to uid, or
nilif there is no such user.
This function returns the user name corresponding to Emacs's real UID. This ignores the effective UID, and the environment variables LOGNAME and USER.
This function returns the full name of the logged-in user—or the value of the environment variable NAME, if that is set.
If the Emacs process's user-id does not correspond to any known user (and provided
NAMEis not set), the result is"unknown".If uid is non-
nil, then it should be a number (a user-id) or a string (a login name). Thenuser-full-namereturns the full name corresponding to that user-id or login name. If you specify a user-id or login name that isn't defined, it returnsnil.
The symbols user-login-name, user-real-login-name and
user-full-name are variables as well as functions. The functions
return the same values that the variables hold. These variables allow
you to fake out Emacs by telling the functions what to return. The
variables are also useful for constructing frame titles (see Frame Titles).
This function returns the real UID of the user. The value may be floating point, in the (unlikely) event that the UID is too large to fit in a Lisp integer.
This function returns the effective UID of the user. The value may be floating point.
This function returns the effective GID of the Emacs process. The value may be floating point.
This function returns the real GID of the Emacs process. The value may be floating point.
This function returns a list of strings, listing the user names on the system. If Emacs cannot retrieve this information, the return value is a list containing just the value of
user-real-login-name.
This function returns a list of strings, listing the names of user groups on the system. If Emacs cannot retrieve this information, the return value is
nil.
This section explains how to determine the current time and time zone.
Most of these functions represent time as a list of four integers
(sec-high sec-low microsec picosec).
This represents the number of seconds from the epoch (January
1, 1970 at 00:00 UTC), using the formula:
high * 2**16 + low + micro * 10**−6 +
pico * 10**−12.
The return value of current-time represents time using this
form, as do the timestamps in the return values of other functions
such as file-attributes (see Definition of file-attributes). In some cases, functions may return two- or
three-element lists, with omitted microsec and picosec
components defaulting to zero.
Function arguments, e.g., the time argument to
current-time-string, accept a more-general time value
format, which can be a list of integers as above, or a single number
for seconds since the epoch, or nil for the current time. You
can convert a time value into a human-readable string using
current-time-string and format-time-string, into a list
of integers using seconds-to-time, and into other forms using
decode-time and float-time. These functions are
described in the following sections.
This function returns the current time and date as a human-readable string. The format does not vary for the initial part of the string, which contains the day of week, month, day of month, and time of day in that order: the number of characters used for these fields is always the same, so you can reliably use
substringto extract them. You should count characters from the beginning of the string rather than from the end, as the year might not have exactly four digits, and additional information may some day be added at the end.The argument time, if given, specifies a time to format, instead of the current time. The optional argument zone defaults to the current time zone rule. See Time Zone Rules.
(current-time-string) => "Wed Oct 14 22:21:05 1987"
This function returns the current time, represented as a list of four integers
(sec-high sec-low microsec picosec). These integers have trailing zeros on systems that return time with lower resolutions. On all current machines picosec is a multiple of 1000, but this may change as higher-resolution clocks become available.
This function returns the current time as a floating-point number of seconds since the epoch. The optional argument time, if given, specifies a time to convert instead of the current time.
Warning: Since the result is floating point, it may not be exact. Do not use this function if precise time stamps are required.
time-to-secondsis an alias for this function.
This function converts a time value to list-of-integer form. For example, if time is a number,
(time-to-seconds (seconds-to-timetime))equals the number unless overflow or rounding errors occur.
The default time zone is determined by the TZ environment
variable. See System Environment. For example, you can tell Emacs
to default to Universal Time with (setenv "TZ" "UTC0"). If
TZ is not in the environment, Emacs uses system wall clock time,
which is a platform-dependent default time zone.
The set of supported TZ strings is system-dependent. GNU and many other systems support the tzdata database, e.g., `"America/New_York"' specifies the time zone and daylight saving time history for locations near New York City. GNU and most other systems support POSIX-style TZ strings, e.g., `"EST+5EDT,M4.1.0/2,M10.5.0/2"' specifies the rules used in New York from 1987 through 2006. All systems support the string `"UTC0"' meaning Universal Time.
Functions that convert to and from local time accept an optional
time zone rule argument, which specifies the conversion's time
zone and daylight saving time history. If the time zone rule is
omitted or nil, the conversion uses Emacs's default time zone.
If it is t, the conversion uses Universal Time. If it is
wall, the conversion uses the system wall clock time. If it is
a string, the conversion uses the time zone rule equivalent to setting
TZ to that string.
This function returns a list describing the time zone that the user is in.
The value has the form
(offset abbr). Here offset is an integer giving the number of seconds ahead of Universal Time (east of Greenwich). A negative value means west of Greenwich. The second element, abbr, is a string giving an abbreviation for the time zone, e.g., `"CST"' for China Standard Time or for U.S. Central Standard Time. Both elements can change when daylight saving time begins or ends; if the user has specified a time zone that does not use a seasonal time adjustment, then the value is constant through time.If the operating system doesn't supply all the information necessary to compute the value, the unknown elements of the list are
nil.The argument time, if given, specifies a time value to analyze instead of the current time. The optional argument zone defaults to the current time zone rule.
These functions convert time values (see Time of Day) into calendrical information and vice versa.
Many 32-bit operating systems are limited to system times containing 32 bits of information in their seconds component; these systems typically handle only the times from 1901-12-13 20:45:52 through 2038-01-19 03:14:07 Universal Time. However, 64-bit and some 32-bit operating systems have larger seconds components, and can represent times far in the past or future.
Time conversion functions always use the Gregorian calendar, even for dates before the Gregorian calendar was introduced. Year numbers count the number of years since the year 1 B.C., and do not skip zero as traditional Gregorian years do; for example, the year number −37 represents the Gregorian year 38 B.C.
This function converts a time value into calendrical information. If you don't specify time, it decodes the current time, and similarly zone defaults to the current time zone rule. See Time Zone Rules. The return value is a list of nine elements, as follows:
(seconds minutes hour day month year dow dst utcoff)Here is what the elements mean:
- seconds
- The number of seconds past the minute, as an integer between 0 and 59. On some operating systems, this is 60 for leap seconds.
- minutes
- The number of minutes past the hour, as an integer between 0 and 59.
- hour
- The hour of the day, as an integer between 0 and 23.
- day
- The day of the month, as an integer between 1 and 31.
- month
- The month of the year, as an integer between 1 and 12.
- year
- The year, an integer typically greater than 1900.
- dow
- The day of week, as an integer between 0 and 6, where 0 stands for Sunday.
- dst
tif daylight saving time is effect, otherwisenil.
- utcoff
- An integer indicating the Universal Time offset in seconds, i.e., the number of seconds east of Greenwich.
Common Lisp Note: Common Lisp has different meanings for dow and utcoff.
This function is the inverse of
decode-time. It converts seven items of calendrical data into a list-of-integer time value. For the meanings of the arguments, see the table above underdecode-time.Year numbers less than 100 are not treated specially. If you want them to stand for years above 1900, or years above 2000, you must alter them yourself before you call
encode-time.The optional argument zone defaults to the current time zone rule. See Time Zone Rules. In addition to the usual time zone rule values, it can also be a list (as you would get from
current-time-zone) or an integer (as fromdecode-time), applied without any further alteration for daylight saving time.If you pass more than seven arguments to
encode-time, the first six are used as seconds through year, the last argument is used as zone, and the arguments in between are ignored. This feature makes it possible to use the elements of a list returned bydecode-timeas the arguments toencode-time, like this:(apply 'encode-time (decode-time ...))You can perform simple date arithmetic by using out-of-range values for the seconds, minutes, hour, day, and month arguments; for example, day 0 means the day preceding the given month.
The operating system puts limits on the range of possible time values; if you try to encode a time that is out of range, an error results. For instance, years before 1970 do not work on some systems; on others, years as early as 1901 do work.
These functions convert time values to text in a string, and vice versa. Time values are lists of two to four integers (see Time of Day).
This function parses the time-string string and returns the corresponding time value.
This function converts time (or the current time, if time is omitted) to a string according to format-string. The conversion uses the time zone rule zone, which defaults to the current time zone rule. See Time Zone Rules. The argument format-string may contain `%'-sequences which say to substitute parts of the time. Here is a table of what the `%'-sequences mean:
- `%a'
- This stands for the abbreviated name of the day of week.
- `%A'
- This stands for the full name of the day of week.
- `%b'
- This stands for the abbreviated name of the month.
- `%B'
- This stands for the full name of the month.
- `%c'
- This is a synonym for `%x %X'.
- `%C'
- This has a locale-specific meaning. In the default locale (named C), it is equivalent to `%A, %B %e, %Y'.
- `%d'
- This stands for the day of month, zero-padded.
- `%D'
- This is a synonym for `%m/%d/%y'.
- `%e'
- This stands for the day of month, blank-padded.
- `%h'
- This is a synonym for `%b'.
- `%H'
- This stands for the hour (00–23).
- `%I'
- This stands for the hour (01–12).
- `%j'
- This stands for the day of the year (001–366).
- `%k'
- This stands for the hour (0–23), blank padded.
- `%l'
- This stands for the hour (1–12), blank padded.
- `%m'
- This stands for the month (01–12).
- `%M'
- This stands for the minute (00–59).
- `%n'
- This stands for a newline.
- `%N'
- This stands for the nanoseconds (000000000–999999999). To ask for fewer digits, use `%3N' for milliseconds, `%6N' for microseconds, etc. Any excess digits are discarded, without rounding.
- `%p'
- This stands for `AM' or `PM', as appropriate.
- `%r'
- This is a synonym for `%I:%M:%S %p'.
- `%R'
- This is a synonym for `%H:%M'.
- `%S'
- This stands for the seconds (00–59).
- `%t'
- This stands for a tab character.
- `%T'
- This is a synonym for `%H:%M:%S'.
- `%U'
- This stands for the week of the year (01–52), assuming that weeks start on Sunday.
- `%w'
- This stands for the numeric day of week (0–6). Sunday is day 0.
- `%W'
- This stands for the week of the year (01–52), assuming that weeks start on Monday.
- `%x'
- This has a locale-specific meaning. In the default locale (named `C'), it is equivalent to `%D'.
- `%X'
- This has a locale-specific meaning. In the default locale (named `C'), it is equivalent to `%T'.
- `%y'
- This stands for the year without century (00–99).
- `%Y'
- This stands for the year with century.
- `%Z'
- This stands for the time zone abbreviation (e.g., `EST').
- `%z'
- This stands for the time zone numerical offset (e.g., `-0500').
You can also specify the field width and type of padding for any of these `%'-sequences. This works as in
printf: you write the field width as digits in the middle of a `%'-sequences. If you start the field width with `0', it means to pad with zeros. If you start the field width with `_', it means to pad with spaces.For example, `%S' specifies the number of seconds since the minute; `%03S' means to pad this with zeros to 3 positions, `%_3S' to pad with spaces to 3 positions. Plain `%3S' pads with zeros, because that is how `%S' normally pads to two positions.
The characters `E' and `O' act as modifiers when used between `%' and one of the letters in the table above. `E' specifies using the current locale's alternative version of the date and time. In a Japanese locale, for example,
%Exmight yield a date format based on the Japanese Emperors' reigns. `E' is allowed in `%Ec', `%EC', `%Ex', `%EX', `%Ey', and `%EY'.`O' means to use the current locale's alternative representation of numbers, instead of the ordinary decimal digits. This is allowed with most letters, all the ones that output numbers.
This function uses the C library function
strftime(see Formatting Calendar Time) to do most of the work. In order to communicate with that function, it first encodes its argument using the coding system specified bylocale-coding-system(see Locales); afterstrftimereturns the resulting string,format-time-stringdecodes the string using that same coding system.
This function converts its argument seconds into a string of years, days, hours, etc., according to format-string. The argument format-string may contain `%'-sequences which control the conversion. Here is a table of what the `%'-sequences mean:
- `%y'
- `%Y'
- The integer number of 365-day years.
- `%d'
- `%D'
- The integer number of days.
- `%h'
- `%H'
- The integer number of hours.
- `%m'
- `%M'
- The integer number of minutes.
- `%s'
- `%S'
- The integer number of seconds.
- `%z'
- Non-printing control flag. When it is used, other specifiers must be given in the order of decreasing size, i.e., years before days, hours before minutes, etc. Nothing will be produced in the result string to the left of `%z' until the first non-zero conversion is encountered. For example, the default format used by
emacs-uptime(see emacs-uptime)"%Y, %D, %H, %M, %z%S"means that the number of seconds will always be produced, but years, days, hours, and minutes will only be shown if they are non-zero.
- `%%'
- Produces a literal `%'.
Upper-case format sequences produce the units in addition to the numbers, lower-case formats produce only the numbers.
You can also specify the field width by following the `%' with a number; shorter numbers will be padded with blanks. An optional period before the width requests zero-padding instead. For example,
"%.3Y"might produce"004 years".Warning: This function works only with values of seconds that don't exceed
most-positive-fixnum(see most-positive-fixnum).
Emacs provides several functions and primitives that return time, both elapsed and processor time, used by the Emacs process.
This function returns a string representing the Emacs uptime—the elapsed wall-clock time this instance of Emacs is running. The string is formatted by
format-secondsaccording to the optional argument format. For the available format descriptors, see format-seconds. If format isnilor omitted, it defaults to"%Y, %D, %H, %M, %z%S".When called interactively, it prints the uptime in the echo area.
This function returns the processor run time used by Emacs as a list of four integers:
(sec-high sec-low microsec picosec), using the same format ascurrent-time(see Time of Day).Note that the time returned by this function excludes the time Emacs was not using the processor, and if the Emacs process has several threads, the returned value is the sum of the processor times used up by all Emacs threads.
If the system doesn't provide a way to determine the processor run time,
get-internal-run-timereturns the same time ascurrent-time.
This function returns the duration of the Emacs initialization (see Startup Summary) in seconds, as a string. When called interactively, it prints the duration in the echo area.
These functions perform calendrical computations using time values (see Time of Day).
This returns the time difference t1 − t2 between two time values, as a time value.
This returns the sum of two time values, as a time value. One argument should represent a time difference rather than a point in time. Here is how to add a number of seconds to a time value:
(time-add time seconds)
This function returns the number of days between the beginning of year 1 and time-value.
This returns the day number within the year corresponding to time-value.
You can set up a timer to call a function at a specified future time or after a certain length of idleness.
Emacs cannot run timers at any arbitrary point in a Lisp program; it
can run them only when Emacs could accept output from a subprocess:
namely, while waiting or inside certain primitive functions such as
sit-for or read-event which can wait. Therefore, a
timer's execution may be delayed if Emacs is busy. However, the time of
execution is very precise if Emacs is idle.
Emacs binds inhibit-quit to t before calling the timer
function, because quitting out of many timer functions can leave
things in an inconsistent state. This is normally unproblematical
because most timer functions don't do a lot of work. Indeed, for a
timer to call a function that takes substantial time to run is likely
to be annoying. If a timer function needs to allow quitting, it
should use with-local-quit (see Quitting). For example, if
a timer function calls accept-process-output to receive output
from an external process, that call should be wrapped inside
with-local-quit, to ensure that C-g works if the external
process hangs.
It is usually a bad idea for timer functions to alter buffer
contents. When they do, they usually should call undo-boundary
both before and after changing the buffer, to separate the timer's
changes from user commands' changes and prevent a single undo entry
from growing to be quite large.
Timer functions should also avoid calling functions that cause Emacs
to wait, such as sit-for (see Waiting). This can lead to
unpredictable effects, since other timers (or even the same timer) can
run while waiting. If a timer function needs to perform an action
after a certain time has elapsed, it can do this by scheduling a new
timer.
If a timer function calls functions that can change the match data, it should save and restore the match data. See Saving Match Data.
This sets up a timer that calls the function function with arguments args at time time. If repeat is a number (integer or floating point), the timer is scheduled to run again every repeat seconds after time. If repeat is
nil, the timer runs only once.time may specify an absolute or a relative time.
Absolute times may be specified using a string with a limited variety of formats, and are taken to be times today, even if already in the past. The recognized forms are `xxxx', `x:xx', or `xx:xx' (military time), and `xxam', `xxAM', `xxpm', `xxPM', `xx:xxam', `xx:xxAM', `xx:xxpm', or `xx:xxPM'. A period can be used instead of a colon to separate the hour and minute parts.
To specify a relative time as a string, use numbers followed by units. For example:
- `1 min'
- denotes 1 minute from now.
- `1 min 5 sec'
- denotes 65 seconds from now.
- `1 min 2 sec 3 hour 4 day 5 week 6 fortnight 7 month 8 year'
- denotes exactly 103 months, 123 days, and 10862 seconds from now.
For relative time values, Emacs considers a month to be exactly thirty days, and a year to be exactly 365.25 days.
Not all convenient formats are strings. If time is a number (integer or floating point), that specifies a relative time measured in seconds. The result of
encode-timecan also be used to specify an absolute value for time.In most cases, repeat has no effect on when first call takes place—time alone specifies that. There is one exception: if time is
t, then the timer runs whenever the time is a multiple of repeat seconds after the epoch. This is useful for functions likedisplay-time.The function
run-at-timereturns a timer value that identifies the particular scheduled future action. You can use this value to callcancel-timer(see below).
A repeating timer nominally ought to run every repeat seconds, but remember that any invocation of a timer can be late. Lateness of one repetition has no effect on the scheduled time of the next repetition. For instance, if Emacs is busy computing for long enough to cover three scheduled repetitions of the timer, and then starts to wait, it will immediately call the timer function three times in immediate succession (presuming no other timers trigger before or between them). If you want a timer to run again no less than n seconds after the last invocation, don't use the repeat argument. Instead, the timer function should explicitly reschedule the timer.
This variable's value specifies the maximum number of times to repeat calling a timer function in a row, when many previously scheduled calls were unavoidably delayed.
Execute body, but give up after seconds seconds. If body finishes before the time is up,
with-timeoutreturns the value of the last form in body. If, however, the execution of body is cut short by the timeout, thenwith-timeoutexecutes all the timeout-forms and returns the value of the last of them.This macro works by setting a timer to run after seconds seconds. If body finishes before that time, it cancels the timer. If the timer actually runs, it terminates execution of body, then executes timeout-forms.
Since timers can run within a Lisp program only when the program calls a primitive that can wait,
with-timeoutcannot stop executing body while it is in the midst of a computation—only when it calls one of those primitives. So usewith-timeoutonly with a body that waits for input, not one that does a long computation.
The function y-or-n-p-with-timeout provides a simple way to use
a timer to avoid waiting too long for an answer. See Yes-or-No Queries.
This cancels the requested action for timer, which should be a timer—usually, one previously returned by
run-at-timeorrun-with-idle-timer. This cancels the effect of that call to one of these functions; the arrival of the specified time will not cause anything special to happen.
Here is how to set up a timer that runs when Emacs is idle for a certain length of time. Aside from how to set them up, idle timers work just like ordinary timers.
Set up a timer which runs the next time Emacs is idle for secs seconds. The value of secs may be a number or a value of the type returned by
current-idle-time.If repeat is
nil, the timer runs just once, the first time Emacs remains idle for a long enough time. More often repeat is non-nil, which means to run the timer each time Emacs remains idle for secs seconds.The function
run-with-idle-timerreturns a timer value which you can use in callingcancel-timer(see Timers).
Emacs becomes idle when it starts waiting for user input, and
it remains idle until the user provides some input. If a timer is set
for five seconds of idleness, it runs approximately five seconds after
Emacs first becomes idle. Even if repeat is non-nil,
this timer will not run again as long as Emacs remains idle, because
the duration of idleness will continue to increase and will not go
down to five seconds again.
Emacs can do various things while idle: garbage collect, autosave or handle data from a subprocess. But these interludes during idleness do not interfere with idle timers, because they do not reset the clock of idleness to zero. An idle timer set for 600 seconds will run when ten minutes have elapsed since the last user command was finished, even if subprocess output has been accepted thousands of times within those ten minutes, and even if there have been garbage collections and autosaves.
When the user supplies input, Emacs becomes non-idle while executing the input. Then it becomes idle again, and all the idle timers that are set up to repeat will subsequently run another time, one by one.
Do not write an idle timer function containing a loop which does a
certain amount of processing each time around, and exits when
(input-pending-p) is non-nil. This approach seems very
natural but has two problems:
Similarly, do not write an idle timer function that sets up another idle timer (including the same idle timer) with secs argument less than or equal to the current idleness time. Such a timer will run almost immediately, and continue running again and again, instead of waiting for the next time Emacs becomes idle. The correct approach is to reschedule with an appropriate increment of the current value of the idleness time, as described below.
If Emacs is idle, this function returns the length of time Emacs has been idle, as a list of four integers:
(sec-high sec-low microsec picosec), using the same format ascurrent-time(see Time of Day).When Emacs is not idle,
current-idle-timereturnsnil. This is a convenient way to test whether Emacs is idle.
The main use of current-idle-time is when an idle timer
function wants to “take a break” for a while. It can set up another
idle timer to call the same function again, after a few seconds more
idleness. Here's an example:
(defvar my-resume-timer nil
"Timer for `my-timer-function' to reschedule itself, or nil.")
(defun my-timer-function ()
;; If the user types a command while my-resume-timer
;; is active, the next time this function is called from
;; its main idle timer, deactivate my-resume-timer.
(when my-resume-timer
(cancel-timer my-resume-timer))
...do the work for a while...
(when taking-a-break
(setq my-resume-timer
(run-with-idle-timer
;; Compute an idle time break-length
;; more than the current value.
(time-add (current-idle-time) break-length)
nil
'my-timer-function))))
This section describes functions and variables for recording or manipulating terminal input. See Display, for related functions.
This function sets the mode for reading keyboard input. If interrupt is non-
nil, then Emacs uses input interrupts. If it isnil, then it uses cbreak mode. The default setting is system-dependent. Some systems always use cbreak mode regardless of what is specified.When Emacs communicates directly with X, it ignores this argument and uses interrupts if that is the way it knows how to communicate.
If flow is non-
nil, then Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This has no effect except in cbreak mode.The argument meta controls support for input character codes above 127. If meta is
t, Emacs converts characters with the 8th bit set into Meta characters. If meta isnil, Emacs disregards the 8th bit; this is necessary when the terminal uses it as a parity bit. If meta is neithertnornil, Emacs uses all 8 bits of input unchanged. This is good for terminals that use 8-bit character sets.If quit-char is non-
nil, it specifies the character to use for quitting. Normally this character is C-g. See Quitting.
The current-input-mode function returns the input mode settings
Emacs is currently using.
This function returns the current mode for reading keyboard input. It returns a list, corresponding to the arguments of
set-input-mode, of the form(interrupt flow meta quit)in which:
- interrupt
- is non-
nilwhen Emacs is using interrupt-driven input. Ifnil, Emacs is using cbreak mode.
- flow
- is non-
nilif Emacs uses xon/xoff (C-q, C-s) flow control for output to the terminal. This value is meaningful only when interrupt isnil.
- meta
- is
tif Emacs treats the eighth bit of input characters as the meta bit;nilmeans Emacs clears the eighth bit of every input character; any other value means Emacs uses all eight bits as the basic character code.
- quit
- is the character Emacs currently uses for quitting, usually C-g.
This function returns a vector containing the last 300 input events from the keyboard or mouse. All input events are included, whether or not they were used as parts of key sequences. Thus, you always get the last 300 input events, not counting events generated by keyboard macros. (These are excluded because they are less interesting for debugging; it should be enough to see the events that invoked the macros.)
A call to
clear-this-command-keys(see Command Loop Info) causes this function to return an empty vector immediately afterward.
This function opens a dribble file named filename. When a dribble file is open, each input event from the keyboard or mouse (but not those from keyboard macros) is written in that file. A non-character event is expressed using its printed representation surrounded by `<...>'. Be aware that sensitive information (such as passwords) may end up recorded in the dribble file.
You close the dribble file by calling this function with an argument of
nil.
See also the open-termscript function (see Terminal Output).
The terminal output functions send output to a text terminal, or keep
track of output sent to the terminal. The variable baud-rate
tells you what Emacs thinks is the output speed of the terminal.
This variable's value is the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations such as padding.
It also affects decisions about whether to scroll part of the screen or repaint on text terminals. See Forcing Redisplay, for the corresponding functionality on graphical terminals.
The value is measured in baud.
If you are running across a network, and different parts of the
network work at different baud rates, the value returned by Emacs may be
different from the value used by your local terminal. Some network
protocols communicate the local terminal speed to the remote machine, so
that Emacs and other programs can get the proper value, but others do
not. If Emacs has the wrong value, it makes decisions that are less
than optimal. To fix the problem, set baud-rate.
This function sends string to terminal without alteration. Control characters in string have terminal-dependent effects. (If you need to display non-ASCII text on the terminal, encode it using one of the functions described in Explicit Encoding.) This function operates only on text terminals. terminal may be a terminal object, a frame, or
nilfor the selected frame's terminal. In batch mode, string is sent tostdoutwhen terminal isnil.One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how (on certain terminals) to define function key 4 to move forward four characters (by transmitting the characters C-u C-f to the computer):
(send-string-to-terminal "\eF4\^U\^F") => nil
This function is used to open a termscript file that will record all the characters sent by Emacs to the terminal. It returns
nil. Termscript files are useful for investigating problems where Emacs garbles the screen, problems that are due to incorrect Termcap entries or to undesirable settings of terminal options more often than to actual Emacs bugs. Once you are certain which characters were actually output, you can determine reliably whether they correspond to the Termcap specifications in use.(open-termscript "../junk/termscript") => nilYou close the termscript file by calling this function with an argument of
nil.See also
open-dribble-filein Recording Input.
To play sound using Emacs, use the function play-sound. Only
certain systems are supported; if you call play-sound on a
system which cannot really do the job, it gives an error.
The sound must be stored as a file in RIFF-WAVE format (`.wav') or Sun Audio format (`.au').
This function plays a specified sound. The argument, sound, has the form
(soundproperties...), where the properties consist of alternating keywords (particular symbols recognized specially) and values corresponding to them.Here is a table of the keywords that are currently meaningful in sound, and their meanings:
:filefile- This specifies the file containing the sound to play. If the file name is not absolute, it is expanded against the directory
data-directory.
:datadata- This specifies the sound to play without need to refer to a file. The value, data, should be a string containing the same bytes as a sound file. We recommend using a unibyte string.
:volumevolume- This specifies how loud to play the sound. It should be a number in the range of 0 to 1. The default is to use whatever volume has been specified before.
:devicedevice- This specifies the system device on which to play the sound, as a string. The default device is system-dependent.
Before actually playing the sound,
play-soundcalls the functions in the listplay-sound-functions. Each function is called with one argument, sound.
This function is an alternative interface to playing a sound file specifying an optional volume and device.
A list of functions to be called before playing a sound. Each function is called with one argument, a property list that describes the sound.
To define system-specific X11 keysyms, set the variable
system-key-alist.
This variable's value should be an alist with one element for each system-specific keysym. Each element has the form
(code.symbol), where code is the numeric keysym code (not including the vendor-specific bit, −2**28), and symbol is the name for the function key.For example
(168 . mute-acute)defines a system-specific key (used by HP X servers) whose numeric code is −2**28 + 168.It is not crucial to exclude from the alist the keysyms of other X servers; those do no harm, as long as they don't conflict with the ones used by the X server actually in use.
The variable is always local to the current terminal, and cannot be buffer-local. See Multiple Terminals.
You can specify which keysyms Emacs should use for the Meta, Alt, Hyper, and Super modifiers by setting these variables:
The name of the keysym that should stand for the Alt modifier (respectively, for Meta, Hyper, and Super). For example, here is how to swap the Meta and Alt modifiers within Emacs:
(setq x-alt-keysym 'meta) (setq x-meta-keysym 'alt)
The command-line option `-batch' causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with `-l file', which loads the library named file, or `-f function', which calls function with no arguments, or `--eval form'.
Any Lisp program output that would normally go to the echo area,
either using message, or using prin1, etc., with
t as the stream, goes instead to Emacs's standard descriptors
when in batch mode: message writes to the standard error
descriptor, while prin1 and other print functions write to the
standard output. Similarly, input that would normally come from the
minibuffer is read from the standard input descriptor. Thus, Emacs
behaves much like a noninteractive application program. (The echo
area output that Emacs itself normally generates, such as command
echoing, is suppressed entirely.)
Non-ASCII text written to the standard output or error descriptors is
by default encoded using locale-coding-system (see Locales)
if it is non-nil; this can be overridden by binding
coding-system-for-write to a coding system of you choice
(see Explicit Encoding).
Emacs supports the X Session Management Protocol, which is used to suspend and restart applications. In the X Window System, a program called the session manager is responsible for keeping track of the applications that are running. When the X server shuts down, the session manager asks applications to save their state, and delays the actual shutdown until they respond. An application can also cancel the shutdown.
When the session manager restarts a suspended session, it directs these applications to individually reload their saved state. It does this by specifying a special command-line argument that says what saved session to restore. For Emacs, this argument is `--smid session'.
Emacs supports saving state via a hook called
emacs-save-session-functions. Emacs runs this hook when the session manager tells it that the window system is shutting down. The functions are called with no arguments, and with the current buffer set to a temporary buffer. Each function can useinsertto add Lisp code to this buffer. At the end, Emacs saves the buffer in a file, called the session file.Subsequently, when the session manager restarts Emacs, it loads the session file automatically (see Loading). This is performed by a function named
emacs-session-restore, which is called during startup. See Startup Summary.If a function in
emacs-save-session-functionsreturns non-nil, Emacs tells the session manager to cancel the shutdown.
Here is an example that just inserts some text into *scratch* when Emacs is restarted by the session manager.
(add-hook 'emacs-save-session-functions 'save-yourself-test)
(defun save-yourself-test ()
(insert "(save-current-buffer
(switch-to-buffer \"*scratch*\")
(insert \"I am restored\"))")
nil)
Emacs is able to send notifications on systems that support the
freedesktop.org Desktop Notifications Specification and on MS-Windows.
In order to use this functionality on Posix hosts, Emacs must have
been compiled with D-Bus support, and the notifications library
must be loaded. See D-Bus.
The following function is supported when D-Bus support is available:
This function sends a notification to the desktop via D-Bus, consisting of the parameters specified by the params arguments. These arguments should consist of alternating keyword and value pairs. The supported keywords and values are as follows:
:busbus- The D-Bus bus. This argument is needed only if a bus other than
:sessionshall be used.
:titletitle- The notification title.
:bodytext- The notification body text. Depending on the implementation of the notification server, the text could contain HTML markups, like `"<b>bold text</b>"', hyperlinks, or images. Special HTML characters must be encoded, as `"Contact <postmaster@localhost>!"'.
:app-namename- The name of the application sending the notification. The default is
notifications-application-name.
:replaces-idid- The notification id that this notification replaces. id must be the result of a previous
notifications-notifycall.
:app-iconicon-file- The file name of the notification icon. If set to
nil, no icon is displayed. The default isnotifications-application-icon.
:actions (key title key title...)- A list of actions to be applied. key and title are both strings. The default action (usually invoked by clicking the notification) should have a key named `"default"'. The title can be anything, though implementations are free not to display it.
:timeouttimeout- The timeout time in milliseconds since the display of the notification at which the notification should automatically close. If −1, the notification's expiration time is dependent on the notification server's settings, and may vary for the type of notification. If 0, the notification never expires. Default value is −1.
:urgencyurgency- The urgency level. It can be
low,normal, orcritical.
:action-items- When this keyword is given, the title string of the actions is interpreted as icon name.
:categorycategory- The type of notification this is, a string. See the Desktop Notifications Specification for a list of standard categories.
:desktop-entryfilename- This specifies the name of the desktop filename representing the calling program, like `"emacs"'.
:image-data (width height rowstride has-alpha bits channels data)- This is a raw data image format that describes the width, height, rowstride, whether there is an alpha channel, bits per sample, channels and image data, respectively.
:image-pathpath- This is represented either as a URI (`file://' is the only URI schema supported right now) or a name in a freedesktop.org-compliant icon theme from `$XDG_DATA_DIRS/icons'.
:sound-filefilename- The path to a sound file to play when the notification pops up.
:sound-namename- A themable named sound from the freedesktop.org sound naming specification from `$XDG_DATA_DIRS/sounds', to play when the notification pops up. Similar to the icon name, only for sounds. An example would be `"message-new-instant"'.
:suppress-sound- Causes the server to suppress playing any sounds, if it has that ability.
:resident- When set the server will not automatically remove the notification when an action has been invoked. The notification will remain resident in the server until it is explicitly removed by the user or by the sender. This hint is likely only useful when the server has the
:persistencecapability.
:transient- When set the server will treat the notification as transient and by-pass the server's persistence capability, if it should exist.
:xposition:yposition- Specifies the X, Y location on the screen that the notification should point to. Both arguments must be used together.
:on-actionfunction- Function to call when an action is invoked. The notification id and the key of the action are passed as arguments to the function.
:on-closefunction- Function to call when the notification has been closed by timeout or by the user. The function receive the notification id and the closing reason as arguments:
expiredif the notification has expireddismissedif the notification was dismissed by the userclose-notificationif the notification was closed by a call tonotifications-close-notificationundefinedif the notification server hasn't provided a reasonWhich parameters are accepted by the notification server can be checked via
notifications-get-capabilities.This function returns a notification id, an integer, which can be used to manipulate the notification item with
notifications-close-notificationor the:replaces-idargument of anothernotifications-notifycall. For example:(defun my-on-action-function (id key) (message "Message %d, key \"%s\" pressed" id key)) => my-on-action-function (defun my-on-close-function (id reason) (message "Message %d, closed due to \"%s\"" id reason)) => my-on-close-function (notifications-notify :title "Title" :body "This is <b>important</b>." :actions '("Confirm" "I agree" "Refuse" "I disagree") :on-action 'my-on-action-function :on-close 'my-on-close-function) => 22 A message window opens on the desktop. Press ``I agree''. => Message 22, key "Confirm" pressed Message 22, closed due to "dismissed"
This function closes a notification with identifier id. bus can be a string denoting a D-Bus connection, the default is
:session.
Returns the capabilities of the notification server, a list of symbols. bus can be a string denoting a D-Bus connection, the default is
:session. The following capabilities can be expected:
:actions- The server will provide the specified actions to the user.
:body- Supports body text.
:body-hyperlinks- The server supports hyperlinks in the notifications.
:body-images- The server supports images in the notifications.
:body-markup- Supports markup in the body text.
:icon-multi- The server will render an animation of all the frames in a given image array.
:icon-static- Supports display of exactly 1 frame of any given image array. This value is mutually exclusive with
:icon-multi.
:persistence- The server supports persistence of notifications.
:sound- The server supports sounds on notifications.
Further vendor-specific caps start with
:x-vendor, like:x-gnome-foo-cap.
Return information on the notification server, a list of strings. bus can be a string denoting a D-Bus connection, the default is
:session. The returned list is(name vendor version spec-version).
- name
- The product name of the server.
- vendor
- The vendor name. For example, `"KDE"', `"GNOME"'.
- version
- The server's version number.
- spec-version
- The specification version the server is compliant with.
If spec_version is
nil, the server supports a specification prior to `"1.0"'.
When Emacs runs on MS-Windows as a GUI session, it supports a small subset of the D-Bus notifications functionality via a native primitive:
This function displays an MS-Windows tray notification as specified by params. MS-Windows tray notifications are displayed in a balloon from an icon in the notification area of the taskbar.
Value is the integer unique ID of the notification that can be used to remove the notification using
w32-notification-close, described below. If the function fails, the return value isnil.The arguments params are specified as keyword/value pairs. All the parameters are optional, but if no parameters are specified, the function will do nothing and return
nil.The following parameters are supported:
:iconicon- Display icon in the system tray. If icon is a string, it should specify a file name from which to load the icon; the specified file should be a .ico Windows icon file. If icon is not a string, or if this parameter is not specified, the standard Emacs icon will be used.
:tiptip- Use tip as the tooltip for the notification. If tip is a string, this is the text of a tooltip that will be shown when the mouse pointer hovers over the tray icon added by the notification. If tip is not a string, or if this parameter is not specified, the default tooltip text is `Emacs notification'. The tooltip text can be up to 127 characters long (63 on Windows versions before W2K). Longer strings will be truncated.
:levellevel- Notification severity level, one of
info,warning, orerror. If given, the value determines the icon displayed to the left of the notification title, but only if the:titleparameter (see below) is also specified and is a string.
:titletitle- The title of the notification. If title is a string, it is displayed in a larger font immediately above the body text. The title text can be up to 63 characters long; longer text will be truncated.
:bodybody- The body of the notification. If body is a string, it specifies the text of the notification message. Use embedded newlines to control how the text is broken into lines. The body text can be up to 255 characters long, and will be truncated if it's longer. Unlike with D-Bus, the body text should be plain text, with no markup.
Note that versions of Windows before W2K support only
:iconand:tip. The other parameters can be passed, but they will be ignored on those old systems.There can be at most one active notification at any given time. An active notification must be removed by calling
w32-notification-closebefore a new one can be shown.
To remove the notification and its icon from the taskbar, use the following function:
This function removes the tray notification given by its unique id.
Several operating systems support watching of filesystems for changes of files. If configured properly, Emacs links a respective library like inotify, kqueue, gfilenotify, or w32notify statically. These libraries enable watching of filesystems on the local machine.
It is also possible to watch filesystems on remote machines, see Remote Files This does not depend on one of the libraries linked to Emacs.
Since all these libraries emit different events on notified file
changes, there is the Emacs library filenotify which provides a
unique interface.
Add a watch for filesystem events pertaining to file. This arranges for filesystem events pertaining to file to be reported to Emacs.
The returned value is a descriptor for the added watch. Its type depends on the underlying library, it cannot be assumed to be an integer as in the example below. It should be used for comparison by
equalonly.If the file cannot be watched for some reason, this function signals a
file-notify-errorerror.Sometimes, mounted filesystems cannot be watched for file changes. This is not detected by this function, a non-
nilreturn value does not guarantee that changes on file will be notified.flags is a list of conditions to set what will be watched for. It can include the following symbols:
change- watch for file changes
attribute-change- watch for file attribute changes, like permissions or modification time
If file is a directory, changes for all files in that directory will be notified. This does not work recursively.
When any event happens, Emacs will call the callback function passing it a single argument event, which is of the form
(descriptor action file [file1])descriptor is the same object as the one returned by this function. action is the description of the event. It could be any one of the following symbols:
created- file was created
deleted- file was deleted
changed- file's contents has changed; with w32notify library, reports attribute changes as well
renamed- file has been renamed to file1
attribute-changed- a file attribute was changed
stopped- watching file has been stopped
Note that the w32notify library does not report
attribute-changedevents. When some file's attribute, like permissions or modification time, has changed, this library reports achangedevent. Likewise, the kqueue library does not report reliably file attribute changes when watching a directory.The
stoppedevent reports, that watching the file has been stopped. This could be becausefile-notify-rm-watchwas called (see below), or because the file being watched was deleted, or due to another error reported from the underlying library.file and file1 are the name of the file(s) whose event is being reported. For example:
(require 'filenotify) => filenotify (defun my-notify-callback (event) (message "Event %S" event)) => my-notify-callback (file-notify-add-watch "/tmp" '(change attribute-change) 'my-notify-callback) => 35025468 (write-region "foo" nil "/tmp/foo") => Event (35025468 created "/tmp/.#foo") Event (35025468 created "/tmp/foo") Event (35025468 changed "/tmp/foo") Event (35025468 deleted "/tmp/.#foo") (write-region "bla" nil "/tmp/foo") => Event (35025468 created "/tmp/.#foo") Event (35025468 changed "/tmp/foo") Event (35025468 deleted "/tmp/.#foo") (set-file-modes "/tmp/foo" (default-file-modes)) => Event (35025468 attribute-changed "/tmp/foo")Whether the action
renamedis returned, depends on the used watch library. Otherwise, the actionsdeletedandcreatedcould be returned in a random order.(rename-file "/tmp/foo" "/tmp/bla") => Event (35025468 renamed "/tmp/foo" "/tmp/bla") (delete-file "/tmp/bla") => Event (35025468 deleted "/tmp/bla")
Removes an existing file watch specified by its descriptor. descriptor should be an object returned by
file-notify-add-watch.
Checks a watch specified by its descriptor for validity. descriptor should be an object returned by
file-notify-add-watch.A watch can become invalid if the file or directory it watches is deleted, or if the watcher thread exits abnormally for any other reason. Removing the watch by calling
file-notify-rm-watchalso makes it invalid.(make-directory "/tmp/foo") => Event (35025468 created "/tmp/foo") (setq desc (file-notify-add-watch "/tmp/foo" '(change) 'my-notify-callback)) => 11359632 (file-notify-valid-p desc) => t (write-region "bla" nil "/tmp/foo/bla") => Event (11359632 created "/tmp/foo/.#bla") Event (11359632 created "/tmp/foo/bla") Event (11359632 changed "/tmp/foo/bla") Event (11359632 deleted "/tmp/foo/.#bla") ;; Deleting a file in the directory doesn't invalidate the watch. (delete-file "/tmp/foo/bla") => Event (11359632 deleted "/tmp/foo/bla") (write-region "bla" nil "/tmp/foo/bla") => Event (11359632 created "/tmp/foo/.#bla") Event (11359632 created "/tmp/foo/bla") Event (11359632 changed "/tmp/foo/bla") Event (11359632 deleted "/tmp/foo/.#bla") ;; Deleting the directory invalidates the watch. ;; Events arrive for different watch descriptors. (delete-directory "/tmp/foo" 'recursive) => Event (35025468 deleted "/tmp/foo") Event (11359632 deleted "/tmp/foo/bla") Event (11359632 deleted "/tmp/foo") Event (11359632 stopped "/tmp/foo") (file-notify-valid-p desc) => nil
A dynamically loaded library is a library that is loaded on demand, when its facilities are first needed. Emacs supports such on-demand loading of support libraries for some of its features.
This is an alist of dynamic libraries and external library files implementing them.
Each element is a list of the form
(libraryfiles...), where thecaris a symbol representing a supported external library, and the rest are strings giving alternate filenames for that library.Emacs tries to load the library from the files in the order they appear in the list; if none is found, the Emacs session won't have access to that library, and the features it provides will be unavailable.
Image support on some platforms uses this facility. Here's an example of setting this variable for supporting images on MS-Windows:
(setq dynamic-library-alist '((xpm "libxpm.dll" "xpm4.dll" "libXpm-nox4.dll") (png "libpng12d.dll" "libpng12.dll" "libpng.dll" "libpng13d.dll" "libpng13.dll") (jpeg "jpeg62.dll" "libjpeg.dll" "jpeg-62.dll" "jpeg.dll") (tiff "libtiff3.dll" "libtiff.dll") (gif "giflib4.dll" "libungif4.dll" "libungif.dll") (svg "librsvg-2-2.dll") (gdk-pixbuf "libgdk_pixbuf-2.0-0.dll") (glib "libglib-2.0-0.dll") (gobject "libgobject-2.0-0.dll")))Note that image types
pbmandxbmdo not need entries in this variable because they do not depend on external libraries and are always available in Emacs.Also note that this variable is not meant to be a generic facility for accessing external libraries; only those already known by Emacs can be loaded through it.
This variable is ignored if the given library is statically linked into Emacs.
Like any application, Emacs can be run in a secure environment, where the operating system enforces rules about access and the like. With some care, Emacs-based applications can also be part of a security perimeter that checks such rules. Although the default settings for Emacs work well for a typical software development environment, they may require adjustment in environments containing untrusted users that may include attackers. Here is a compendium of security issues that may be helpful if you are developing such applications. It is by no means complete; it is intended to give you an idea of the security issues involved, rather than to be a security checklist.
safe-local-variable too optimistically, a problem that is all
too common. To disable this feature for both files and directories,
set enable-local-variables to nil.
read-passwd. See Reading a Password.
Although these functions do not attempt to
broadcast passwords to the world, their implementations are not proof
against determined attackers with access to Emacs internals. For
example, even if Elisp code uses clear-string to scrub a password from
its memory after using it, remnants of the password may still reside
in the garbage-collected free list. See Modifying Strings.
mv a b, because either file name might start
with `-', or might contain shell metacharacters like `;'.
Although functions like shell-quote-argument can help avoid
this sort of problem, they are not panaceas; for example, on a POSIX
platform shell-quote-argument quotes shell metacharacters but
not leading `-'. See Shell Arguments. Typically it is safer
to use call-process than a subshell. See Synchronous Processes. And it is safer yet to use builtin Emacs functions; for
example, use (rename-file "a" "b" t) instead of
invoking mv. See Changing Files.
Emacs has customization and other variables with similar
considerations. For example, if the variable shell-file-name
specifies a shell with nonstandard behavior, an Emacs-based
application may misbehave.
tramp-mode to nil, file names using a certain
syntax are interpreted as being network files, and are retrieved
across the network. See The Tramp Manual.
(file-readable-p "foo.txt") returns t, it could be that
foo.txt is unreadable because some other program changed the
file's permissions between the call to file-readable-p and now.
See Testing Accessibility.
Emacs provides a standard way to distribute Emacs Lisp code to users. A package is a collection of one or more files, formatted and bundled in such a way that users can easily download, install, uninstall, and upgrade it.
The following sections describe how to create a package, and how to put it in a package archive for others to download. See Packages, for a description of user-level features of the packaging system.
A package is either a simple package or a multi-file package. A simple package is stored in a package archive as a single Emacs Lisp file, while a multi-file package is stored as a tar file (containing multiple Lisp files, and possibly non-Lisp files such as a manual).
In ordinary usage, the difference between simple packages and multi-file packages is relatively unimportant; the Package Menu interface makes no distinction between them. However, the procedure for creating them differs, as explained in the following sections.
Each package (whether simple or multi-file) has certain attributes:
version-to-list
understands (e.g., `11.86'). Each release of a package should be
accompanied by an increase in the version number.
describe-package), following the package's brief description
and installation status. It normally spans multiple lines, and should
fully describe the package's capabilities and how to begin using it
once it is installed.
Installing a package, either via the command package-install-file,
or via the Package Menu, creates a subdirectory of
package-user-dir named name-version, where
name is the package's name and version its version
(e.g., ~/.emacs.d/elpa/auctex-11.86/). We call this the
package's content directory. It is where Emacs puts the
package's contents (the single Lisp file for a simple package, or the
files extracted from a multi-file package).
Emacs then searches every Lisp file in the content directory for
autoload magic comments (see Autoload). These autoload
definitions are saved to a file named name-autoloads.el
in the content directory. They are typically used to autoload the
principal user commands defined in the package, but they can also
perform other tasks, such as adding an element to
auto-mode-alist (see Auto Major Mode). Note that a package
typically does not autoload every function and variable defined
within it—only the handful of commands typically called to begin
using the package. Emacs then byte-compiles every Lisp file in the
package.
After installation, the installed package is loaded: Emacs
adds the package's content directory to load-path, and
evaluates the autoload definitions in name-autoloads.el.
Whenever Emacs starts up, it automatically calls the function
package-initialize to load installed packages. This is done
after loading the init file and abbrev file (if any) and before
running after-init-hook (see Startup Summary). Automatic
package loading is disabled if the user option
package-enable-at-startup is nil.
This function initializes Emacs' internal record of which packages are installed, and loads them. The user option
package-load-listspecifies which packages to load; by default, all installed packages are loaded. If called during startup, this function also setspackage-enable-at-startuptonil, to avoid accidentally loading the packages twice. See Package Installation.The optional argument no-activate, if non-
nil, causes Emacs to update its record of installed packages without actually loading them; it is for internal use only.
A simple package consists of a single Emacs Lisp source file. The file must conform to the Emacs Lisp library header conventions (see Library Headers). The package's attributes are taken from the various headers, as illustrated by the following example:
;;; superfrobnicator.el --- Frobnicate and bifurcate flanges
;; Copyright (C) 2011 Free Software Foundation, Inc.
;; Author: J. R. Hacker <jrh@example.com>
;; Version: 1.3
;; Package-Requires: ((flange "1.0"))
;; Keywords: multimedia, frobnicate
;; URL: http://example.com/jrhacker/superfrobnicate
...
;;; Commentary:
;; This package provides a minor mode to frobnicate and/or
;; bifurcate any flanges you desire. To activate it, just type
...
;;;###autoload
(define-minor-mode superfrobnicator-mode
...
The name of the package is the same as the base name of the file, as written on the first line. Here, it is `superfrobnicator'.
The brief description is also taken from the first line. Here, it is `Frobnicate and bifurcate flanges'.
The version number comes from the `Package-Version' header, if it exists, or from the `Version' header otherwise. One or the other must be present. Here, the version number is 1.3.
If the file has a `;;; Commentary:' section, this section is used as the long description. (When displaying the description, Emacs omits the `;;; Commentary:' line, as well as the leading comment characters in the commentary itself.)
If the file has a `Package-Requires' header, that is used as the package dependencies. In the above example, the package depends on the `flange' package, version 1.0 or higher. See Library Headers, for a description of the `Package-Requires' header. If the header is omitted, the package has no dependencies.
The `Keywords' and `URL' headers are optional, but recommended.
The command describe-package uses these to add links to its
output. The `Keywords' header should contain at least one
standard keyword from the finder-known-keywords list.
The file ought to also contain one or more autoload magic comments,
as explained in Packaging Basics. In the above example, a magic
comment autoloads superfrobnicator-mode.
See Package Archives, for a explanation of how to add a single-file package to a package archive.
A multi-file package is less convenient to create than a single-file package, but it offers more features: it can include multiple Emacs Lisp files, an Info manual, and other file types (such as images).
Prior to installation, a multi-file package is stored in a package archive as a tar file. The tar file must be named name-version.tar, where name is the package name and version is the version number. Its contents, once extracted, must all appear in a directory named name-version, the content directory (see Packaging Basics). Files may also extract into subdirectories of the content directory.
One of the files in the content directory must be named
name-pkg.el. It must contain a single Lisp form,
consisting of a call to the function define-package, described
below. This defines the package's version, brief description, and
requirements.
For example, if we distribute version 1.3 of the superfrobnicator as a multi-file package, the tar file would be superfrobnicator-1.3.tar. Its contents would extract into the directory superfrobnicator-1.3, and one of these would be the file superfrobnicator-pkg.el.
This function defines a package. name is the package name, a string. version is the version, as a string of a form that can be understood by the function
version-to-list. docstring is the brief description.requirements is a list of required packages and their versions. Each element in this list should have the form
(dep-name dep-version), where dep-name is a symbol whose name is the dependency's package name, and dep-version is the dependency's version (a string).
If the content directory contains a file named README, this file is used as the long description.
If the content directory contains a file named dir, this is
assumed to be an Info directory file made with install-info.
See Invoking install-info. The relevant Info files should also
be present in the content directory. In this case, Emacs will
automatically add the content directory to Info-directory-list
when the package is activated.
Do not include any .elc files in the package. Those are created when the package is installed. Note that there is no way to control the order in which files are byte-compiled.
Do not include any file named name-autoloads.el. This file is reserved for the package's autoload definitions (see Packaging Basics). It is created automatically when the package is installed, by searching all the Lisp files in the package for autoload magic comments.
If the multi-file package contains auxiliary data files (such as
images), the package's Lisp code can refer to these files via the
variable load-file-name (see Loading). Here is an example:
(defconst superfrobnicator-base (file-name-directory load-file-name))
(defun superfrobnicator-fetch-image (file)
(expand-file-name file superfrobnicator-base))
Via the Package Menu, users may download packages from package
archives. Such archives are specified by the variable
package-archives, whose default value contains a single entry:
the archive hosted by the GNU project at http://elpa.gnu.org. This
section describes how to set up and maintain a package archive.
The value of this variable is an alist of package archives recognized by the Emacs package manager.
Each alist element corresponds to one archive, and should have the form
(id.location), where id is the name of the archive (a string) and location is its base location (a string).If the base location starts with `http:', it is treated as a HTTP URL, and packages are downloaded from this archive via HTTP (as is the case for the default GNU archive).
Otherwise, the base location should be a directory name. In this case, Emacs retrieves packages from this archive via ordinary file access. Such local archives are mainly useful for testing.
A package archive is simply a directory in which the package files, and associated files, are stored. If you want the archive to be reachable via HTTP, this directory must be accessible to a web server. How to accomplish this is beyond the scope of this manual.
A convenient way to set up and update a package archive is via the
package-x library. This is included with Emacs, but not loaded
by default; type M-x load-library <RET> package-x <RET> to
load it, or add (require 'package-x) to your init file.
See Lisp Libraries.
Once loaded, you can make use of the following:
The value of this variable is the base location of a package archive, as a directory name. The commands in the
package-xlibrary will use this base location.The directory name should be absolute. You may specify a remote name, such as /ssh:foo@example.com:/var/www/packages/, if the package archive is on a different machine. See Remote Files.
This command prompts for filename, a file name, and uploads that file to
package-archive-upload-base. The file must be either a simple package (a .el file) or a multi-file package (a .tar file); otherwise, an error is raised. The package attributes are automatically extracted, and the archive's contents list is updated with this information.If
package-archive-upload-basedoes not specify a valid directory, the function prompts interactively for one. If the directory does not exist, it is created. The directory need not have any initial contents (i.e., you can use this command to populate an initially empty archive).
This command is similar to
package-upload-file, but instead of prompting for a package file, it uploads the contents of the current buffer. The current buffer must be visiting a simple package (a .el file) or a multi-file package (a .tar file); otherwise, an error is raised.
After you create an archive, remember that it is not accessible in the
Package Menu interface unless it is in package-archives.
Maintaining a public package archive entails a degree of responsibility. When Emacs users install packages from your archive, those packages can cause Emacs to run arbitrary code with the permissions of the installing user. (This is true for Emacs code in general, not just for packages.) So you should ensure that your archive is well-maintained and keep the hosting system secure.
One way to increase the security of your packages is to sign them using a cryptographic key. If you have generated a private/public gpg key pair, you can use gpg to sign the package like this:
gpg -ba -o file.sig file
For a single-file package, file is the package Lisp file; for a multi-file package, it is the package tar file. You can also sign the archive's contents file in the same way. Make the .sig files available in the same location as the packages. You should also make your public key available for people to download; e.g., by uploading it to a key server such as http://pgp.mit.edu/. When people install packages from your archive, they can use your public key to verify the signatures.
A full explanation of these matters is outside the scope of this manual. For more information on cryptographic keys and signing, see GnuPG. Emacs comes with an interface to GNU Privacy Guard, see EasyPG.
For those users who live backwards in time, here is information about downgrading to Emacs version 23.4. We hope you will enjoy the greater simplicity that results from the absence of many Emacs 25.0.95 features.
lexical-binding variable has been
removed, and so has the lexical argument to eval. The
defvar and defconst forms no longer mark variables as
dynamic, since all variables are dynamic.
Having only dynamic binding follows the spirit of Emacs extensibility, for it allows any Emacs code to access any defined variable with a minimum of fuss. But See Dynamic Binding Tips, for tips to avoid making your programs hard to understand.
nil or omitted argument
does not enable the minor mode unconditionally; instead, it toggles
the minor mode—which is the straightforward thing to do, since that
is the behavior when invoked interactively. One downside is that it
is more troublesome to enable minor modes from hooks; you have to do
something like
(add-hook 'foo-hook (lambda () (bar-mode 1)))
or define turn-on-bar-mode and call that from the hook.
prog-mode dummy major mode has been removed. Instead of
using it as a crutch to meet programming mode conventions, you should
explicitly ensure that your mode follows those conventions.
See Major Mode Conventions.
bidi-string-mark-left-to-right has been removed; so have many
other functions and variables related to bidirectional display.
Unicode directionality characters like U+200E LEFT-TO-RIGHT
MARK have no special effect on display.
window-parent, window parameters related to window arrangement,
and window-local buffer lists have all been removed. Functions for
resizing windows can delete windows if they become too small.
The action-function feature for controlling buffer display has
been removed, including display-buffer-overriding-action and
related variables, as well as the action argument to
display-buffer and other functions. The way to
programmatically control how Emacs chooses a window to display a
buffer is to bind the right combination of pop-up-frames and
other variables.
completion-extra-properties variable, the metadata
action flag for completion functions, and the concept of
completion categories. Lisp programmers may now find the choice
of methods for tuning completion less bewildering, but if a package
finds the streamlined interface insufficient for its needs, it must
implement its own specialized completion feature.
copy-directory now behaves the same whether or not the
destination is an existing directory: if the destination exists, the
contents of the first directory are copied into it (with
subdirectories handled recursively), rather than copying the first
directory into a subdirectory.
delete-file and
delete-directory have been removed. The variable
delete-by-moving-to-trash must now be used with care; whenever
it is non-nil, all calls to delete-file or
delete-directory use the trash.
copy-file has been
removed. The return value of backup-buffer no longer has an
entry for the SELinux file context.
(type item-name cache . binding)
The cache entry is used internally by Emacs to record equivalent keyboard key sequences for invoking the same command; Lisp programs should never use it.
gnutls library has been removed, and the function
open-network-stream correspondingly simplified.
Lisp programs that want an encrypted network connection must now call
external utilities such as starttls or gnutls-cli.
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.
This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.
This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.
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Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
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Permission is granted to copy, distribute and/or modify this document
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If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
Copyright © 2007 Free Software Foundation, Inc. http://fsf.org/
Everyone is permitted to copy and distribute verbatim copies of this
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The GNU General Public License is a free, copyleft license for software and other kinds of works.
The licenses for most software and other practical works are designed to take away your freedom to share and change the works. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change all versions of a program—to make sure it remains free software for all its users. We, the Free Software Foundation, use the GNU General Public License for most of our software; it applies also to any other work released this way by its authors. You can apply it to your programs, too.
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However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.
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Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, you do not qualify to receive new licenses for the same material under section 10.
You are not required to accept this License in order to receive or run a copy of the Program. Ancillary propagation of a covered work occurring solely as a consequence of using peer-to-peer transmission to receive a copy likewise does not require acceptance. However, nothing other than this License grants you permission to propagate or modify any covered work. These actions infringe copyright if you do not accept this License. Therefore, by modifying or propagating a covered work, you indicate your acceptance of this License to do so.
Each time you convey a covered work, the recipient automatically receives a license from the original licensors, to run, modify and propagate that work, subject to this License. You are not responsible for enforcing compliance by third parties with this License.
An “entity transaction” is a transaction transferring control of an organization, or substantially all assets of one, or subdividing an organization, or merging organizations. If propagation of a covered work results from an entity transaction, each party to that transaction who receives a copy of the work also receives whatever licenses to the work the party's predecessor in interest had or could give under the previous paragraph, plus a right to possession of the Corresponding Source of the work from the predecessor in interest, if the predecessor has it or can get it with reasonable efforts.
You may not impose any further restrictions on the exercise of the rights granted or affirmed under this License. For example, you may not impose a license fee, royalty, or other charge for exercise of rights granted under this License, and you may not initiate litigation (including a cross-claim or counterclaim in a lawsuit) alleging that any patent claim is infringed by making, using, selling, offering for sale, or importing the Program or any portion of it.
A “contributor” is a copyright holder who authorizes use under this License of the Program or a work on which the Program is based. The work thus licensed is called the contributor's “contributor version”.
A contributor's “essential patent claims” are all patent claims owned or controlled by the contributor, whether already acquired or hereafter acquired, that would be infringed by some manner, permitted by this License, of making, using, or selling its contributor version, but do not include claims that would be infringed only as a consequence of further modification of the contributor version. For purposes of this definition, “control” includes the right to grant patent sublicenses in a manner consistent with the requirements of this License.
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If you convey a covered work, knowingly relying on a patent license, and the Corresponding Source of the work is not available for anyone to copy, free of charge and under the terms of this License, through a publicly available network server or other readily accessible means, then you must either (1) cause the Corresponding Source to be so available, or (2) arrange to deprive yourself of the benefit of the patent license for this particular work, or (3) arrange, in a manner consistent with the requirements of this License, to extend the patent license to downstream recipients. “Knowingly relying” means you have actual knowledge that, but for the patent license, your conveying the covered work in a country, or your recipient's use of the covered work in a country, would infringe one or more identifiable patents in that country that you have reason to believe are valid.
If, pursuant to or in connection with a single transaction or arrangement, you convey, or propagate by procuring conveyance of, a covered work, and grant a patent license to some of the parties receiving the covered work authorizing them to use, propagate, modify or convey a specific copy of the covered work, then the patent license you grant is automatically extended to all recipients of the covered work and works based on it.
A patent license is “discriminatory” if it does not include within the scope of its coverage, prohibits the exercise of, or is conditioned on the non-exercise of one or more of the rights that are specifically granted under this License. You may not convey a covered work if you are a party to an arrangement with a third party that is in the business of distributing software, under which you make payment to the third party based on the extent of your activity of conveying the work, and under which the third party grants, to any of the parties who would receive the covered work from you, a discriminatory patent license (a) in connection with copies of the covered work conveyed by you (or copies made from those copies), or (b) primarily for and in connection with specific products or compilations that contain the covered work, unless you entered into that arrangement, or that patent license was granted, prior to 28 March 2007.
Nothing in this License shall be construed as excluding or limiting any implied license or other defenses to infringement that may otherwise be available to you under applicable patent law.
If conditions are imposed on you (whether by court order, agreement or otherwise) that contradict the conditions of this License, they do not excuse you from the conditions of this License. If you cannot convey a covered work so as to satisfy simultaneously your obligations under this License and any other pertinent obligations, then as a consequence you may not convey it at all. For example, if you agree to terms that obligate you to collect a royalty for further conveying from those to whom you convey the Program, the only way you could satisfy both those terms and this License would be to refrain entirely from conveying the Program.
Notwithstanding any other provision of this License, you have permission to link or combine any covered work with a work licensed under version 3 of the GNU Affero General Public License into a single combined work, and to convey the resulting work. The terms of this License will continue to apply to the part which is the covered work, but the special requirements of the GNU Affero General Public License, section 13, concerning interaction through a network will apply to the combination as such.
The Free Software Foundation may publish revised and/or new versions of the GNU General Public License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns.
Each version is given a distinguishing version number. If the Program specifies that a certain numbered version of the GNU General Public License “or any later version” applies to it, you have the option of following the terms and conditions either of that numbered version or of any later version published by the Free Software Foundation. If the Program does not specify a version number of the GNU General Public License, you may choose any version ever published by the Free Software Foundation.
If the Program specifies that a proxy can decide which future versions of the GNU General Public License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Program.
Later license versions may give you additional or different permissions. However, no additional obligations are imposed on any author or copyright holder as a result of your choosing to follow a later version.
THERE IS NO WARRANTY FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM “AS IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
If the disclaimer of warranty and limitation of liability provided above cannot be given local legal effect according to their terms, reviewing courts shall apply local law that most closely approximates an absolute waiver of all civil liability in connection with the Program, unless a warranty or assumption of liability accompanies a copy of the Program in return for a fee.
If you develop a new program, and you want it to be of the greatest possible use to the public, the best way to achieve this is to make it free software which everyone can redistribute and change under these terms.
To do so, attach the following notices to the program. It is safest to attach them to the start of each source file to most effectively state the exclusion of warranty; and each file should have at least the “copyright” line and a pointer to where the full notice is found.
one line to give the program's name and a brief idea of what it does.
Copyright (C) year name of author
This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
General Public License for more details.
You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
Also add information on how to contact you by electronic and paper mail.
If the program does terminal interaction, make it output a short notice like this when it starts in an interactive mode:
program Copyright (C) year name of author
This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `show c' for details.
The hypothetical commands `show w' and `show c' should show the appropriate parts of the General Public License. Of course, your program's commands might be different; for a GUI interface, you would use an “about box”.
You should also get your employer (if you work as a programmer) or school, if any, to sign a “copyright disclaimer” for the program, if necessary. For more information on this, and how to apply and follow the GNU GPL, see http://www.gnu.org/licenses/.
The GNU General Public License does not permit incorporating your program into proprietary programs. If your program is a subroutine library, you may consider it more useful to permit linking proprietary applications with the library. If this is what you want to do, use the GNU Lesser General Public License instead of this License. But first, please read http://www.gnu.org/philosophy/why-not-lgpl.html.
This chapter describes no additional features of Emacs Lisp. Instead it gives advice on making effective use of the features described in the previous chapters, and describes conventions Emacs Lisp programmers should follow.
You can automatically check some of the conventions described below by
running the command M-x checkdoc RET when visiting a Lisp file.
It cannot check all of the conventions, and not all the warnings it
gives necessarily correspond to problems, but it is worth examining them
all. Alternatively, use the command M-x checkdoc-current-buffer RET
to check the conventions in the current buffer, or checkdoc-file
when you want to check a file in batch mode, e.g., with a command run by
M-x compile RET.
Here are conventions that you should follow when writing Emacs Lisp code intended for widespread use:
This convention is mandatory for any file that includes custom definitions. If fixing such a file to follow this convention requires an incompatible change, go ahead and make the incompatible change; don't postpone it.
Occasionally, for a command name intended for users to use, it is more convenient if some words come before the package's name prefix. And constructs that define functions, variables, etc., work better if they start with `defun' or `defvar', so put the name prefix later on in the name.
This recommendation applies even to names for traditional Lisp
primitives that are not primitives in Emacs Lisp—such as
copy-list. Believe it or not, there is more than one plausible
way to define copy-list. Play it safe; append your name prefix
to produce a name like foo-copy-list or mylib-copy-list
instead.
If you write a function that you think ought to be added to Emacs under
a certain name, such as twiddle-files, don't call it by that name
in your program. Call it mylib-twiddle-files in your program,
and send mail to `bug-gnu-emacs@gnu.org' suggesting we add
it to Emacs. If and when we do, we can change the name easily enough.
If one prefix is insufficient, your package can use two or three alternative common prefixes, so long as they make sense.
provide at the end of each separate Lisp file.
See Named Features.
require to make sure they are loaded.
See Named Features.
(eval-when-compile (require 'bar))
This tells Emacs to load bar just before byte-compiling
foo, so that the macro definition is available during
compilation. Using eval-when-compile avoids loading bar
when the compiled version of foo is used. It should be
called before the first use of the macro in the file. See Compiling Macros.
require that library at the top-level and be done
with it. But if your file contains several independent features, and
only one or two require the extra library, then consider putting
require statements inside the relevant functions rather than at
the top-level. Or use autoload statements to load the extra
library when needed. This way people who don't use those aspects of
your file do not need to load the extra library.
cl-lib library
rather than the old cl library. The latter does not
use a clean namespace (i.e., its definitions do not
start with a `cl-' prefix). If your package loads cl at
run time, that could cause name clashes for users who don't use that
package.
There is no problem with using the cl package at compile
time, with (eval-when-compile (require 'cl)). That's
sufficient for using the macros in the cl package, because the
compiler expands them before generating the byte-code. It is still
better to use the more modern cl-lib in this case, though.
framep and frame-live-p.
-unload-hook, where feature is the name of
the feature the package provides, and make it undo any such changes.
Using unload-feature to unload the file will run this function.
See Unloading.
(defalias 'gnus-point-at-bol
(if (fboundp 'point-at-bol)
'point-at-bol
'line-beginning-position))
eval-after-load and with-eval-after-load in
libraries and packages (see Hooks for Loading). This feature is
meant for personal customizations; using it in a Lisp program is
unclean, because it modifies the behavior of another Lisp file in a
way that's not visible in that file. This is an obstacle for
debugging, much like advising a function in the other package.
follow-link
condition, so that the link obeys mouse-1-click-follows-link.
See Clickable Text. See Buttons, for an easy method of
implementing such clickable links.
Changing all the Emacs major modes to respect this convention was a lot of work; abandoning this convention would make that work go to waste, and inconvenience users. Please comply with it.
The reason for this rule is that a non-prefix binding for <ESC> in any context prevents recognition of escape sequences as function keys in that context.
For a state that accepts ordinary Emacs commands, or more generally any kind of state in which <ESC> followed by a function key or arrow key is potentially meaningful, then you must not define <ESC> <ESC>, since that would preclude recognizing an escape sequence after <ESC>. In these states, you should define <ESC> <ESC> <ESC> as the way to escape. Otherwise, define <ESC> <ESC> instead.
Following these conventions will make your program fit better into Emacs when it runs.
next-line or previous-line in programs; nearly
always, forward-line is more convenient as well as more
predictable and robust. See Text Lines.
In particular, don't use any of these functions:
beginning-of-buffer, end-of-buffer
replace-string, replace-regexp
insert-file, insert-buffer
If you just want to move point, or replace a certain string, or insert a file or buffer's contents, without any of the other features intended for interactive users, you can replace these functions with one or two lines of simple Lisp code.
Vectors are advantageous for tables that are substantial in size and are accessed in random order (not searched front to back), provided there is no need to insert or delete elements (only lists allow that).
message function, not princ. See The Echo Area.
error
(or signal). The function error does not return.
See Signaling Errors.
Don't use message, throw, sleep-for, or
beep to report errors.
yes-or-no-p or
y-or-n-p should start with a capital letter and end with
`? '.
Enter the answer (default 42):
interactive, if you use a Lisp expression to produce a list
of arguments, don't try to provide the correct default values for
region or position arguments. Instead, provide nil for those
arguments if they were not specified, and have the function body
compute the default value when the argument is nil. For
instance, write this:
(defun foo (pos)
(interactive
(list (if specified specified-pos)))
(unless pos (setq pos default-pos))
...)
rather than this:
(defun foo (pos)
(interactive
(list (if specified specified-pos
default-pos)))
...)
This is so that repetition of the command will recompute these defaults based on the current circumstances.
You do not need to take such precautions when you use interactive specs `d', `m' and `r', because they make special arrangements to recompute the argument values on repetition of the command.
Here are ways of improving the execution speed of byte-compiled Lisp programs.
memq, member,
assq, or assoc is even faster than explicit iteration. It
can be worth rearranging a data structure so that one of these primitive
search functions can be used.
byte-compile
property. If the property is non-nil, then the function is
handled specially.
For example, the following input will show you that aref is
compiled specially (see Array Functions):
(get 'aref 'byte-compile)
=> byte-compile-two-args
Note that in this case (and many others), you must first load the
bytecomp library, which defines the byte-compile property.
defvar definitions for these variables, like this:
(defvar foo)
Such a definition has no effect except to tell the compiler
not to warn about uses of the variable foo in this file.
declare-function
statement (see Declaring Functions).
require for that package to avoid compilation warnings
for them. For instance,
(eval-when-compile
(require 'foo))
with-no-warnings. See Compiler Errors.
Here are some tips and conventions for the writing of documentation strings. You can check many of these conventions by running the command M-x checkdoc-minor-mode.
apropos.
You can fill the text if that looks good. Emacs Lisp mode fills
documentation strings to the width specified by
emacs-lisp-docstring-fill-column. However, you can sometimes
make a documentation string much more readable by adjusting its line
breaks with care. Use blank lines between sections if the
documentation string is long.
For a function, the first line should briefly answer the question, “What does this function do?” For a variable, the first line should briefly answer the question, “What does this value mean?”
Don't limit the documentation string to one line; use as many lines as you need to explain the details of how to use the function or variable. Please use complete sentences for the rest of the text too.
eval refers to its first argument as `FORM', because the
actual argument name is form:
Evaluate FORM and return its value.
Also write metasyntactic variables in capital letters, such as when you show the decomposition of a list or vector into subunits, some of which may vary. `KEY' and `VALUE' in the following example illustrate this practice:
The argument TABLE should be an alist whose elements
have the form (KEY . VALUE). Here, KEY is ...
foo, write “foo”, not
“Foo” (which is a different symbol).
This might appear to contradict the policy of writing function argument values, but there is no real contradiction; the argument value is not the same thing as the symbol that the function uses to hold the value.
If this puts a lower-case letter at the beginning of a sentence and that annoys you, rewrite the sentence so that the symbol is not at the start of it.
t and nil without surrounding
punctuation. For example: `CODE can be ‘lambda’, nil, or t'.
See Quotation Marks, for how to
enter curved single quotes.
Documentation strings can also use an older single-quoting convention, which quotes symbols with grave accent ` and apostrophe ': `like-this' rather than ‘like-this’. This older convention was designed for now-obsolete displays in which grave accent and apostrophe were mirror images.
Documentation using either convention is converted to the user's preferred format when it is copied into a help buffer. See Keys in Documentation.
Help mode automatically creates a hyperlink when a documentation string uses a single-quoted symbol name, if the symbol has either a function or a variable definition. You do not need to do anything special to make use of this feature. However, when a symbol has both a function definition and a variable definition, and you want to refer to just one of them, you can specify which one by writing one of the words `variable', `option', `function', or `command', immediately before the symbol name. (Case makes no difference in recognizing these indicator words.) For example, if you write
This function sets the variable `buffer-file-name'.
then the hyperlink will refer only to the variable documentation of
buffer-file-name, and not to its function documentation.
If a symbol has a function definition and/or a variable definition, but those are irrelevant to the use of the symbol that you are documenting, you can write the words `symbol' or `program' before the symbol name to prevent making any hyperlink. For example,
If the argument KIND-OF-RESULT is the symbol `list',
this function returns a list of all the objects
that satisfy the criterion.
does not make a hyperlink to the documentation, irrelevant here, of the
function list.
Normally, no hyperlink is made for a variable without variable documentation. You can force a hyperlink for such variables by preceding them with one of the words `variable' or `option'.
Hyperlinks for faces are only made if the face name is preceded or followed by the word `face'. In that case, only the face documentation will be shown, even if the symbol is also defined as a variable or as a function.
To make a hyperlink to Info documentation, write the single-quoted name of the Info node (or anchor), preceded by `info node', `Info node', `info anchor' or `Info anchor'. The Info file name defaults to `emacs'. For example,
See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
Finally, to create a hyperlink to URLs, write the single-quoted URL, preceded by `URL'. For example,
The home page for the GNU project has more information (see URL
`http://www.gnu.org/').
forward-char.
(This is normally `C-f', but it may be some other character if the
user has moved key bindings.) See Keys in Documentation.
It is not practical to use `\\[...]' very many times, because display of the documentation string will become slow. So use this to describe the most important commands in your major mode, and then use `\\{...}' to display the rest of the mode's keymap.
The argument FOO can be either a number
\(a buffer position) or a string (a file name).
This prevents the open-parenthesis from being treated as the start of a defun (see Defuns).
dired-find-file is:
In Dired, visit the file or directory named on this line.
defcustom. See Defining Variables.
nil values are equivalent and indicate explicitly what
nil and non-nil mean.
We recommend these conventions for comments:
(setq base-version-list ; There was a base
(assoc (substring fn 0 start-vn) ; version to which
file-version-assoc-list)) ; this looks like
; a subversion.
(prog1 (setq auto-fill-function
...
...
;; Update mode line.
(force-mode-line-update)))
We also normally use two semicolons for comments outside functions.
;; This Lisp code is run in Emacs when it is to operate as
;; a server for other processes.
If a function has no documentation string, it should instead have a
two-semicolon comment right before the function, explaining what the
function does and how to call it properly. Explain precisely what
each argument means and how the function interprets its possible
values. It is much better to convert such comments to documentation
strings, though.
When commenting out entire functions, use two semicolons.
;;;; The kill ring
Generally speaking, the M-; (comment-dwim) command
automatically starts a comment of the appropriate type; or indents an
existing comment to the right place, depending on the number of
semicolons.
See Manipulating Comments.
Emacs has conventions for using special comments in Lisp libraries to divide them into sections and give information such as who wrote them. Using a standard format for these items makes it easier for tools (and people) to extract the relevant information. This section explains these conventions, starting with an example:
;;; foo.el --- Support for the Foo programming language
;; Copyright (C) 2010-2016 Your Name
;; Author: Your Name <yourname@example.com>
;; Maintainer: Someone Else <someone@example.com>
;; Created: 14 Jul 2010
;; Keywords: languages
;; Homepage: http://example.com/foo
;; This file is not part of GNU Emacs.
;; This file is free software...
...
;; along with this file. If not, see <http://www.gnu.org/licenses/>.
The very first line should have this format:
;;; filename --- description
The description should be contained in one line. If the file needs a `-*-' specification, put it after description. If this would make the first line too long, use a Local Variables section at the end of the file.
The copyright notice usually lists your name (if you wrote the file). If you have an employer who claims copyright on your work, you might need to list them instead. Do not say that the copyright holder is the Free Software Foundation (or that the file is part of GNU Emacs) unless your file has been accepted into the Emacs distribution. For more information on the form of copyright and license notices, see the guide on the GNU website.
After the copyright notice come several header comment lines, each beginning with `;; header-name:'. Here is a table of the conventional possibilities for header-name:
;; and a tab or at least two spaces.
We recommend including a contact email address, of the form
`<...>'. For example:
;; Author: Your Name <yourname@example.com>
;; Someone Else <someone@example.com>
;; Another Person <another@example.com>
If there is no maintainer line, the person(s) in the Author field
is/are presumed to be the maintainers. Some files in Emacs use
`FSF' for the maintainer. This means that the original author is
no longer responsible for the file, and that it is maintained as part
of Emacs.
finder-by-keyword help command.
Please use that command to see a list of the meaningful keywords. The
command M-x checkdoc-package-keywords RET will find and display
any keywords that are not in finder-known-keywords. If you set
the variable checkdoc-package-keywords-flag non-nil,
checkdoc commands will include the keyword verification in its checks.
This field is how people will find your package when they're looking for things by topic. To separate the keywords, you can use spaces, commas, or both.
The name of this field is unfortunate, since people often assume it is
the place to write arbitrary keywords that describe their package,
rather than just the relevant Finder keywords.
version-to-list. See Packaging Basics.
Its format is a list of lists. The car of each sub-list is the
name of a package, as a symbol. The cadr of each sub-list is
the minimum acceptable version number, as a string. For instance:
;; Package-Requires: ((gnus "1.0") (bubbles "2.7.2"))
The package code automatically defines a package named `emacs' with the version number of the currently running Emacs. This can be used to require a minimal version of Emacs for a package.
Just about every Lisp library ought to have the `Author' and `Keywords' header comment lines. Use the others if they are appropriate. You can also put in header lines with other header names—they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the library file. These should be separated from anything else by blank lines. Here is a table of them:
This chapter describes how the runnable Emacs executable is dumped with the preloaded Lisp libraries in it, how storage is allocated, and some internal aspects of GNU Emacs that may be of interest to C programmers.
This section explains the steps involved in building the Emacs executable. You don't have to know this material to build and install Emacs, since the makefiles do all these things automatically. This information is pertinent to Emacs developers.
Building Emacs requires GNU Make version 3.81 or later.
Compilation of the C source files in the src directory produces an executable file called temacs, also called a bare impure Emacs. It contains the Emacs Lisp interpreter and I/O routines, but not the editing commands.
The command temacs -l loadup would run temacs
and direct it to load loadup.el. The loadup library
loads additional Lisp libraries, which set up the normal Emacs editing
environment. After this step, the Emacs executable is no longer
bare.
Because it takes some time to load the standard Lisp files, the temacs executable usually isn't run directly by users. Instead, as one of the last steps of building Emacs, the command `temacs -batch -l loadup dump' is run. The special `dump' argument causes temacs to dump out an executable program, called emacs, which has all the standard Lisp files preloaded. (The `-batch' argument prevents temacs from trying to initialize any of its data on the terminal, so that the tables of terminal information are empty in the dumped Emacs.)
The dumped emacs executable (also called a pure Emacs)
is the one which is installed. The variable
preloaded-file-list stores a list of the Lisp files preloaded
into the dumped Emacs. If you port Emacs to a new operating system,
and are not able to implement dumping, then Emacs must load
loadup.el each time it starts.
You can specify additional files to preload by writing a library named site-load.el that loads them. You may need to rebuild Emacs with an added definition
#define SITELOAD_PURESIZE_EXTRA n
to make n added bytes of pure space to hold the additional files; see src/puresize.h. (Try adding increments of 20000 until it is big enough.) However, the advantage of preloading additional files decreases as machines get faster. On modern machines, it is usually not advisable.
After loadup.el reads site-load.el, it finds the
documentation strings for primitive and preloaded functions (and
variables) in the file etc/DOC where they are stored, by
calling Snarf-documentation (see Accessing Documentation).
You can specify other Lisp expressions to execute just before dumping by putting them in a library named site-init.el. This file is executed after the documentation strings are found.
If you want to preload function or variable definitions, there are three ways you can do this and make their documentation strings accessible when you subsequently run Emacs:
nil value for byte-compile-dynamic-docstrings
as a local variable in each of these files, and load them with either
site-load.el or site-init.el. (This method has the
drawback that the documentation strings take up space in Emacs all the
time.)
It is not advisable to put anything in site-load.el or
site-init.el that would alter any of the features that users
expect in an ordinary unmodified Emacs. If you feel you must override
normal features for your site, do it with default.el, so that
users can override your changes if they wish. See Startup Summary.
Note that if either site-load.el or site-init.el changes
load-path, the changes will be lost after dumping.
See Library Search. To make a permanent change to
load-path, use the --enable-locallisppath option
of configure.
In a package that can be preloaded, it is sometimes necessary (or
useful) to delay certain evaluations until Emacs subsequently starts
up. The vast majority of such cases relate to the values of
customizable variables. For example, tutorial-directory is a
variable defined in startup.el, which is preloaded. The default
value is set based on data-directory. The variable needs to
access the value of data-directory when Emacs starts, not when
it is dumped, because the Emacs executable has probably been installed
in a different location since it was dumped.
This function delays the initialization of symbol to the next Emacs start. You normally use this function by specifying it as the
:initializeproperty of a customizable variable. (The argument value is unused, and is provided only for compatibility with the form Custom expects.)
In the unlikely event that you need a more general functionality than
custom-initialize-delay provides, you can use
before-init-hook (see Startup Summary).
This function dumps the current state of Emacs into an executable file to-file. It takes symbols from from-file (this is normally the executable file temacs).
If you want to use this function in an Emacs that was already dumped, you must run Emacs with `-batch'.
Emacs Lisp uses two kinds of storage for user-created Lisp objects: normal storage and pure storage. Normal storage is where all the new data created during an Emacs session are kept (see Garbage Collection). Pure storage is used for certain data in the preloaded standard Lisp files—data that should never change during actual use of Emacs.
Pure storage is allocated only while temacs is loading the
standard preloaded Lisp libraries. In the file emacs, it is
marked as read-only (on operating systems that permit this), so that
the memory space can be shared by all the Emacs jobs running on the
machine at once. Pure storage is not expandable; a fixed amount is
allocated when Emacs is compiled, and if that is not sufficient for
the preloaded libraries, temacs allocates dynamic memory for
the part that didn't fit. The resulting image will work, but garbage
collection (see Garbage Collection) is disabled in this situation,
causing a memory leak. Such an overflow normally won't happen unless
you try to preload additional libraries or add features to the
standard ones. Emacs will display a warning about the overflow when
it starts. If this happens, you should increase the compilation
parameter SYSTEM_PURESIZE_EXTRA in the file
src/puresize.h and rebuild Emacs.
This function makes a copy in pure storage of object, and returns it. It copies a string by simply making a new string with the same characters, but without text properties, in pure storage. It recursively copies the contents of vectors and cons cells. It does not make copies of other objects such as symbols, but just returns them unchanged. It signals an error if asked to copy markers.
This function is a no-op except while Emacs is being built and dumped; it is usually called only in preloaded Lisp files.
The value of this variable is the number of bytes of pure storage allocated so far. Typically, in a dumped Emacs, this number is very close to the total amount of pure storage available—if it were not, we would preallocate less.
This variable determines whether
defunshould make a copy of the function definition in pure storage. If it is non-nil, then the function definition is copied into pure storage.This flag is
twhile loading all of the basic functions for building Emacs initially (allowing those functions to be shareable and non-collectible). Dumping Emacs as an executable always writesnilin this variable, regardless of the value it actually has before and after dumping.You should not change this flag in a running Emacs.
When a program creates a list or the user defines a new function (such as by loading a library), that data is placed in normal storage. If normal storage runs low, then Emacs asks the operating system to allocate more memory. Different types of Lisp objects, such as symbols, cons cells, small vectors, markers, etc., are segregated in distinct blocks in memory. (Large vectors, long strings, buffers and certain other editing types, which are fairly large, are allocated in individual blocks, one per object; small strings are packed into blocks of 8k bytes, and small vectors are packed into blocks of 4k bytes).
Beyond the basic vector, a lot of objects like window, buffer, and
frame are managed as if they were vectors. The corresponding C data
structures include the struct vectorlike_header field whose
size member contains the subtype enumerated by enum pvec_type
and an information about how many Lisp_Object fields this structure
contains and what the size of the rest data is. This information is
needed to calculate the memory footprint of an object, and used
by the vector allocation code while iterating over the vector blocks.
It is quite common to use some storage for a while, then release it by (for example) killing a buffer or deleting the last pointer to an object. Emacs provides a garbage collector to reclaim this abandoned storage. The garbage collector operates by finding and marking all Lisp objects that are still accessible to Lisp programs. To begin with, it assumes all the symbols, their values and associated function definitions, and any data presently on the stack, are accessible. Any objects that can be reached indirectly through other accessible objects are also accessible.
When marking is finished, all objects still unmarked are garbage. No matter what the Lisp program or the user does, it is impossible to refer to them, since there is no longer a way to reach them. Their space might as well be reused, since no one will miss them. The second (sweep) phase of the garbage collector arranges to reuse them.
The sweep phase puts unused cons cells onto a free list for future allocation; likewise for symbols and markers. It compacts the accessible strings so they occupy fewer 8k blocks; then it frees the other 8k blocks. Unreachable vectors from vector blocks are coalesced to create largest possible free areas; if a free area spans a complete 4k block, that block is freed. Otherwise, the free area is recorded in a free list array, where each entry corresponds to a free list of areas of the same size. Large vectors, buffers, and other large objects are allocated and freed individually.
Common Lisp note: Unlike other Lisps, GNU Emacs Lisp does not call the garbage collector when the free list is empty. Instead, it simply requests the operating system to allocate more storage, and processing continues untilgc-cons-thresholdbytes have been used.This means that you can make sure that the garbage collector will not run during a certain portion of a Lisp program by calling the garbage collector explicitly just before it (provided that portion of the program does not use so much space as to force a second garbage collection).
This command runs a garbage collection, and returns information on the amount of space in use. (Garbage collection can also occur spontaneously if you use more than
gc-cons-thresholdbytes of Lisp data since the previous garbage collection.)
garbage-collectreturns a list with information on amount of space in use, where each entry has the form `(name size used)' or `(name size used free)'. In the entry, name is a symbol describing the kind of objects this entry represents, size is the number of bytes used by each one, used is the number of those objects that were found live in the heap, and optional free is the number of those objects that are not live but that Emacs keeps around for future allocations. So an overall result is:((consescons-size used-conses free-conses) (symbolssymbol-size used-symbols free-symbols) (miscsmisc-size used-miscs free-miscs) (stringsstring-size used-strings free-strings) (string-bytesbyte-size used-bytes) (vectorsvector-size used-vectors) (vector-slotsslot-size used-slots free-slots) (floatsfloat-size used-floats free-floats) (intervalsinterval-size used-intervals free-intervals) (buffersbuffer-size used-buffers) (heapunit-size total-size free-size))Here is an example:
(garbage-collect) => ((conses 16 49126 8058) (symbols 48 14607 0) (miscs 40 34 56) (strings 32 2942 2607) (string-bytes 1 78607) (vectors 16 7247) (vector-slots 8 341609 29474) (floats 8 71 102) (intervals 56 27 26) (buffers 944 8) (heap 1024 11715 2678))Below is a table explaining each element. Note that last
heapentry is optional and present only if an underlyingmallocimplementation providesmallinfofunction.
- cons-size
- Internal size of a cons cell, i.e.,
sizeof (struct Lisp_Cons).
- used-conses
- The number of cons cells in use.
- free-conses
- The number of cons cells for which space has been obtained from the operating system, but that are not currently being used.
- symbol-size
- Internal size of a symbol, i.e.,
sizeof (struct Lisp_Symbol).
- used-symbols
- The number of symbols in use.
- free-symbols
- The number of symbols for which space has been obtained from the operating system, but that are not currently being used.
- misc-size
- Internal size of a miscellaneous entity, i.e.,
sizeof (union Lisp_Misc), which is a size of the largest type enumerated inenum Lisp_Misc_Type.
- used-miscs
- The number of miscellaneous objects in use. These include markers and overlays, plus certain objects not visible to users.
- free-miscs
- The number of miscellaneous objects for which space has been obtained from the operating system, but that are not currently being used.
- string-size
- Internal size of a string header, i.e.,
sizeof (struct Lisp_String).
- used-strings
- The number of string headers in use.
- free-strings
- The number of string headers for which space has been obtained from the operating system, but that are not currently being used.
- byte-size
- This is used for convenience and equals to
sizeof (char).
- used-bytes
- The total size of all string data in bytes.
- vector-size
- Internal size of a vector header, i.e.,
sizeof (struct Lisp_Vector).
- used-vectors
- The number of vector headers allocated from the vector blocks.
- slot-size
- Internal size of a vector slot, always equal to
sizeof (Lisp_Object).
- used-slots
- The number of slots in all used vectors.
- free-slots
- The number of free slots in all vector blocks.
- float-size
- Internal size of a float object, i.e.,
sizeof (struct Lisp_Float). (Do not confuse it with the native platformfloatordouble.)
- used-floats
- The number of floats in use.
- free-floats
- The number of floats for which space has been obtained from the operating system, but that are not currently being used.
- interval-size
- Internal size of an interval object, i.e.,
sizeof (struct interval).
- used-intervals
- The number of intervals in use.
- free-intervals
- The number of intervals for which space has been obtained from the operating system, but that are not currently being used.
- buffer-size
- Internal size of a buffer, i.e.,
sizeof (struct buffer). (Do not confuse with the value returned bybuffer-sizefunction.)
- used-buffers
- The number of buffer objects in use. This includes killed buffers invisible to users, i.e., all buffers in
all_bufferslist.
- unit-size
- The unit of heap space measurement, always equal to 1024 bytes.
- total-size
- Total heap size, in unit-size units.
- free-size
- Heap space which is not currently used, in unit-size units.
If there was overflow in pure space (see Pure Storage),
garbage-collectreturnsnil, because a real garbage collection cannot be done.
If this variable is non-
nil, Emacs displays a message at the beginning and end of garbage collection. The default value isnil.
This is a normal hook that is run at the end of garbage collection. Garbage collection is inhibited while the hook functions run, so be careful writing them.
The value of this variable is the number of bytes of storage that must be allocated for Lisp objects after one garbage collection in order to trigger another garbage collection. You can use the result returned by
garbage-collectto get an information about size of the particular object type; space allocated to the contents of buffers does not count. Note that the subsequent garbage collection does not happen immediately when the threshold is exhausted, but only the next time the Lisp interpreter is called.The initial threshold value is
GC_DEFAULT_THRESHOLD, defined in alloc.c. Since it's defined inword_sizeunits, the value is 400,000 for the default 32-bit configuration and 800,000 for the 64-bit one. If you specify a larger value, garbage collection will happen less often. This reduces the amount of time spent garbage collecting, but increases total memory use. You may want to do this when running a program that creates lots of Lisp data.You can make collections more frequent by specifying a smaller value, down to 1/10th of
GC_DEFAULT_THRESHOLD. A value less than this minimum will remain in effect only until the subsequent garbage collection, at which timegarbage-collectwill set the threshold back to the minimum.
The value of this variable specifies the amount of consing before a garbage collection occurs, as a fraction of the current heap size. This criterion and
gc-cons-thresholdapply in parallel, and garbage collection occurs only when both criteria are satisfied.As the heap size increases, the time to perform a garbage collection increases. Thus, it can be desirable to do them less frequently in proportion.
The value returned by garbage-collect describes the amount of
memory used by Lisp data, broken down by data type. By contrast, the
function memory-limit provides information on the total amount of
memory Emacs is currently using.
This function returns the address of the last byte Emacs has allocated, divided by 1024. We divide the value by 1024 to make sure it fits in a Lisp integer.
You can use this to get a general idea of how your actions affect the memory usage.
This variable is
tif Emacs is nearly out of memory for Lisp objects, andnilotherwise.
This returns a list of numbers that count the number of objects created in this Emacs session. Each of these counters increments for a certain kind of object. See the documentation string for details.
This functions returns an amount of total system memory and how much of it is free. On an unsupported system, the value may be
nil.
This variable contains the total number of garbage collections done so far in this Emacs session.
This variable contains the total number of seconds of elapsed time during garbage collection so far in this Emacs session, as a floating-point number.
The garbage collector described above is used to manage data visible
from Lisp programs, as well as most of the data internally used by the
Lisp interpreter. Sometimes it may be useful to allocate temporary
internal objects using the C stack of the interpreter. This can help
performance, as stack allocation is typically faster than using heap
memory to allocate and the garbage collector to free. The downside is
that using such objects after they are freed results in undefined
behavior, so uses should be well thought out and carefully debugged by
using the GC_CHECK_MARKED_OBJECTS feature (see
src/alloc.c). In particular, stack-allocated objects should
never be made visible to user Lisp code.
Currently, cons cells and strings can be allocated this way. This
is implemented by C macros like AUTO_CONS and
AUTO_STRING that define a named Lisp_Object with block
lifetime. These objects are not freed by the garbage collector;
instead, they have automatic storage duration, i.e., they are
allocated like local variables and are automatically freed at the end
of execution of the C block that defined the object.
For performance reasons, stack-allocated strings are limited to
ASCII characters, and many of these strings are immutable,
i.e., calling ASET on them produces undefined behavior.
These functions and variables give information about the total amount
of memory allocation that Emacs has done, broken down by data type.
Note the difference between these and the values returned by
garbage-collect; those count objects that currently exist, but
these count the number or size of all allocations, including those for
objects that have since been freed.
The total number of cons cells that have been allocated so far in this Emacs session.
The total number of floats that have been allocated so far in this Emacs session.
The total number of vector cells that have been allocated so far in this Emacs session.
The total number of symbols that have been allocated so far in this Emacs session.
The total number of string characters that have been allocated so far in this session.
The total number of miscellaneous objects that have been allocated so far in this session. These include markers and overlays, plus certain objects not visible to users.
The total number of intervals that have been allocated so far in this Emacs session.
The total number of strings that have been allocated so far in this Emacs session.
The C part of Emacs is portable to C99 or later: C11-specific features such as `<stdalign.h>' and `_Noreturn' are not used without a check, typically at configuration time, and the Emacs build procedure provides a substitute implementation if necessary. Some C11 features, such as anonymous structures and unions, are too difficult to emulate, so they are avoided entirely.
At some point in the future the base C dialect will no doubt change to C11.
Lisp primitives are Lisp functions implemented in C. The details of interfacing the C function so that Lisp can call it are handled by a few C macros. The only way to really understand how to write new C code is to read the source, but we can explain some things here.
An example of a special form is the definition of or, from
eval.c. (An ordinary function would have the same general
appearance.)
DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
doc: /* Eval args until one of them yields non-nil, then return
that value.
The remaining args are not evalled at all.
If all args return nil, return nil.
usage: (or CONDITIONS...) */)
(Lisp_Object args)
{
Lisp_Object val = Qnil;
while (CONSP (args))
{
val = eval_sub (XCAR (args));
if (!NILP (val))
break;
args = XCDR (args);
QUIT;
}
return val;
}
Let's start with a precise explanation of the arguments to the
DEFUN macro. Here is a template for them:
DEFUN (lname, fname, sname, min, max, interactive, doc)
or.
For.
or allows a minimum of zero arguments.
UNEVALLED,
indicating a special form that receives unevaluated arguments, or
MANY, indicating an unlimited number of evaluated arguments (the
equivalent of &rest). Both UNEVALLED and MANY are
macros. If max is a number, it must be more than min but
less than 8.
interactive in a Lisp function. In the case
of or, it is 0 (a null pointer), indicating that or
cannot be called interactively. A value of "" indicates a
function that should receive no arguments when called interactively.
If the value begins with a `"(', the string is evaluated as a
Lisp form. For example:
DEFUN ("foo", Ffoo, Sfoo, 0, UNEVALLED,
"(list (read-char-by-name \"Insert character: \")\
(prefix-numeric-value current-prefix-arg)\
t))",
doc: /* ... /*)
If the last line of the documentation string begins with the keyword `usage:', the rest of the line is treated as the argument list for documentation purposes. This way, you can use different argument names in the documentation string from the ones used in the C code. `usage:' is required if the function has an unlimited number of arguments.
All the usual rules for documentation strings in Lisp code (see Documentation Tips) apply to C code documentation strings too.
After the call to the DEFUN macro, you must write the
argument list for the C function, including the types for the
arguments. If the primitive accepts a fixed maximum number of Lisp
arguments, there must be one C argument for each Lisp argument, and
each argument must be of type Lisp_Object. (Various macros and
functions for creating values of type Lisp_Object are declared
in the file lisp.h.) If the primitive has no upper limit on
the number of Lisp arguments, it must have exactly two C arguments:
the first is the number of Lisp arguments, and the second is the
address of a block containing their values. These have types
int and Lisp_Object * respectively. Since
Lisp_Object can hold any Lisp object of any data type, you
can determine the actual data type only at run time; so if you want
a primitive to accept only a certain type of argument, you must check
the type explicitly using a suitable predicate (see Type Predicates).
Within the function For itself, the local variable
args refers to objects controlled by Emacs's stack-marking
garbage collector. Although the garbage collector does not reclaim
objects reachable from C Lisp_Object stack variables, it may
move non-object components of an object, such as string contents; so
functions that access non-object components must take care to refetch
their addresses after performing Lisp evaluation. Lisp evaluation can
occur via calls to eval_sub or Feval, either directly or
indirectly.
Note the call to the QUIT macro inside the loop: this macro
checks whether the user pressed C-g, and if so, aborts the
processing. You should do that in any loop that can potentially
require a large number of iterations; in this case, the list of
arguments could be very long. This increases Emacs responsiveness and
improves user experience.
You must not use C initializers for static or global variables unless the variables are never written once Emacs is dumped. These variables with initializers are allocated in an area of memory that becomes read-only (on certain operating systems) as a result of dumping Emacs. See Pure Storage.
Defining the C function is not enough to make a Lisp primitive available; you must also create the Lisp symbol for the primitive and store a suitable subr object in its function cell. The code looks like this:
defsubr (&sname);
Here sname is the name you used as the third argument to DEFUN.
If you add a new primitive to a file that already has Lisp primitives
defined in it, find the function (near the end of the file) named
syms_of_something, and add the call to defsubr
there. If the file doesn't have this function, or if you create a new
file, add to it a syms_of_filename (e.g.,
syms_of_myfile). Then find the spot in emacs.c where all
of these functions are called, and add a call to
syms_of_filename there.
The function syms_of_filename is also the place to define
any C variables that are to be visible as Lisp variables.
DEFVAR_LISP makes a C variable of type Lisp_Object visible
in Lisp. DEFVAR_INT makes a C variable of type int
visible in Lisp with a value that is always an integer.
DEFVAR_BOOL makes a C variable of type int visible in Lisp
with a value that is either t or nil. Note that variables
defined with DEFVAR_BOOL are automatically added to the list
byte-boolean-vars used by the byte compiler.
If you want to make a Lisp variables that is defined in C behave
like one declared with defcustom, add an appropriate entry to
cus-start.el.
If you define a file-scope C variable of type Lisp_Object,
you must protect it from garbage-collection by calling staticpro
in syms_of_filename, like this:
staticpro (&variable);
Here is another example function, with more complicated arguments. This comes from the code in window.c, and it demonstrates the use of macros and functions to manipulate Lisp objects.
DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
Scoordinates_in_window_p, 2, 2, 0,
doc: /* Return non-nil if COORDINATES are in WINDOW.
...
or `right-margin' is returned. */)
(register Lisp_Object coordinates, Lisp_Object window)
{
struct window *w;
struct frame *f;
int x, y;
Lisp_Object lx, ly;
CHECK_LIVE_WINDOW (window);
w = XWINDOW (window);
f = XFRAME (w->frame);
CHECK_CONS (coordinates);
lx = Fcar (coordinates);
ly = Fcdr (coordinates);
CHECK_NUMBER_OR_FLOAT (lx);
CHECK_NUMBER_OR_FLOAT (ly);
x = FRAME_PIXEL_X_FROM_CANON_X (f, lx) + FRAME_INTERNAL_BORDER_WIDTH(f);
y = FRAME_PIXEL_Y_FROM_CANON_Y (f, ly) + FRAME_INTERNAL_BORDER_WIDTH(f);
switch (coordinates_in_window (w, x, y))
{
case ON_NOTHING: /* NOT in window at all. */
return Qnil;
...
case ON_MODE_LINE: /* In mode line of window. */
return Qmode_line;
...
case ON_SCROLL_BAR: /* On scroll-bar of window. */
/* Historically we are supposed to return nil in this case. */
return Qnil;
default:
abort ();
}
}
Note that C code cannot call functions by name unless they are defined
in C. The way to call a function written in Lisp is to use
Ffuncall, which embodies the Lisp function funcall. Since
the Lisp function funcall accepts an unlimited number of
arguments, in C it takes two: the number of Lisp-level arguments, and a
one-dimensional array containing their values. The first Lisp-level
argument is the Lisp function to call, and the rest are the arguments to
pass to it.
The C functions call0, call1, call2, and so on,
provide handy ways to call a Lisp function conveniently with a fixed
number of arguments. They work by calling Ffuncall.
eval.c is a very good file to look through for examples; lisp.h contains the definitions for some important macros and functions.
If you define a function which is side-effect free, update the code
in byte-opt.el that binds side-effect-free-fns and
side-effect-and-error-free-fns so that the compiler optimizer
knows about it.
Emacs Lisp provides a rich set of the data types. Some of them, like cons cells, integers and strings, are common to nearly all Lisp dialects. Some others, like markers and buffers, are quite special and needed to provide the basic support to write editor commands in Lisp. To implement such a variety of object types and provide an efficient way to pass objects between the subsystems of an interpreter, there is a set of C data structures and a special type to represent the pointers to all of them, which is known as tagged pointer.
In C, the tagged pointer is an object of type Lisp_Object. Any
initialized variable of such a type always holds the value of one of the
following basic data types: integer, symbol, string, cons cell, float,
vectorlike or miscellaneous object. Each of these data types has the
corresponding tag value. All tags are enumerated by enum Lisp_Type
and placed into a 3-bit bitfield of the Lisp_Object. The rest of the
bits is the value itself. Integers are immediate, i.e., directly
represented by those value bits, and all other objects are represented
by the C pointers to a corresponding object allocated from the heap. Width
of the Lisp_Object is platform- and configuration-dependent: usually
it's equal to the width of an underlying platform pointer (i.e., 32-bit on
a 32-bit machine and 64-bit on a 64-bit one), but also there is a special
configuration where Lisp_Object is 64-bit but all pointers are 32-bit.
The latter trick was designed to overcome the limited range of values for
Lisp integers on a 32-bit system by using 64-bit long long type for
Lisp_Object.
The following C data structures are defined in lisp.h to represent the basic data types beyond integers:
struct Lisp_Consstruct Lisp_Stringstruct Lisp_Vectorstruct Lisp_Symbolstruct Lisp_Floatunion Lisp_MiscThese types are the first-class citizens of an internal type system.
Since the tag space is limited, all other types are the subtypes of either
Lisp_Vectorlike or Lisp_Misc. Vector subtypes are enumerated
by enum pvec_type, and nearly all complex objects like windows, buffers,
frames, and processes fall into this category. The rest of special types,
including markers and overlays, are enumerated by enum Lisp_Misc_Type
and form the set of subtypes of Lisp_Misc.
Below there is a description of a few subtypes of Lisp_Vectorlike.
Buffer object represents the text to display and edit. Window is the part
of display structure which shows the buffer or used as a container to
recursively place other windows on the same frame. (Do not confuse Emacs Lisp
window object with the window as an entity managed by the user interface
system like X; in Emacs terminology, the latter is called frame.) Finally,
process object is used to manage the subprocesses.
Two structures (see buffer.h) are used to represent buffers
in C. The buffer_text structure contains fields describing the
text of a buffer; the buffer structure holds other fields. In
the case of indirect buffers, two or more buffer structures
reference the same buffer_text structure.
Here are some of the fields in struct buffer_text:
beggptgpt_bytezz_bytegap_sizemodiffsave_modiffchars_modiffoverlay_modiffmodiff is incremented after each
buffer-modification event, and is never otherwise changed;
save_modiff contains the value of modiff the last time
the buffer was visited or saved; chars_modiff counts only
modifications to the characters in the buffer, ignoring all other
kinds of changes; and overlay_modiff counts only modifications
to the overlays.
beg_unchangedend_unchangedunchanged_modifiedoverlay_unchanged_modifiedmodiff and overlay_modiff, respectively,
after the last complete redisplay. If their current values match
modiff or overlay_modiff, that means
beg_unchanged and end_unchanged contain no useful
information.
markerschain are the other
markers referring to this buffer text.
intervalsSome of the fields of struct buffer are:
headerstruct vectorlike_header is common to all
vectorlike objects.
own_textstruct buffer_text structure that ordinarily holds the buffer
contents. In indirect buffers, this field is not used.
textbuffer_text structure for this buffer. In an
ordinary buffer, this is the own_text field above. In an
indirect buffer, this is the own_text field of the base buffer.
nextptpt_bytebegvbegv_bytezvzv_bytebase_bufferlocal_flagsDEFVAR_PER_BUFFER, and their buffer-local bindings are stored
in fields in the buffer structure itself. (Some of these fields are
described in this table.)
modtimeauto_save_modifiedlast_window_startwindow-start position in the buffer as of the last time the
buffer was displayed in a window.
clip_changedprevent_redisplay_optimizations_poverlay_centeroverlays_beforeoverlays_afteroverlays_before is sorted in order of decreasing end position,
and overlays_after is sorted in order of increasing beginning
position.
namesave_lengthbuffer_text structure because indirect buffers are never
saved.
directorydefault-directory (see File Name Expansion).
filenamenil. This is
the value of the buffer-local variable buffer-file-name
(see Buffer File Name).
undo_listbacked_upauto_save_file_nameauto_save_file_formatread_onlyfile_formatfile_truenameinvisibility_specdisplay_countdisplay_timebuffer- and have
underscores replaced with dashes. For instance, undo_list
stores the value of buffer-undo-list.
markmarkers. See The Mark.
local_var_alistmajor_modelisp-mode.
mode_name"Lisp".
keymapabbrev_tablesyntax_tablecategory_tabledisplay_tabledowncase_tableupcase_tablecase_canon_tableminor_modespt_markerbegv_markerzv_markerpt, begv, and zv respectively, for this buffer
when the buffer is not current.
mode_line_formatheader_line_formatcase_fold_searchtab_widthfill_columnleft_marginauto_fill_functiontruncate_linesword_wrapctl_arrowbidi_display_reorderingbidi_paragraph_directionselective_displayselective_display_ellipsesoverwrite_modeabbrev_modemark_activeenable_multibyte_charactersbuffer_file_coding_systemcache_long_line_scanspoint_before_scrollleft_fringe_widthright_fringe_widthfringes_outside_marginsscroll_bar_widthindicate_empty_linesindicate_buffer_boundariesfringe_indicator_alistfringe_cursor_alistscroll_up_aggressivelyscroll_down_aggressivelycursor_typecursor_in_non_selected_windowsmode_line_format stores the value of mode-line-format.
last_selected_windownil
if that window no longer displays this buffer.
The fields of a window (for a complete list, see the definition of
struct window in window.h) include:
framemini_pnil if this window is a minibuffer window.
parentParent windows do not display buffers, and play little role in display
except to shape their child windows. Emacs Lisp programs usually have
no access to the parent windows; they operate on the windows at the
leaves of the tree, which actually display buffers.
hchildvchildhchild is used if the window is subdivided
horizontally by child windows, and vchild if it is subdivided
vertically. In a live window, only one of hchild, vchild,
and buffer (q.v.) is non-nil.
nextprevnext is
nil if the window is the right-most or bottom-most in its group;
prev is nil if it is the left-most or top-most in its
group.
left_coltop_linetotal_colstotal_linesbufferstartpointmforce_startnil, it says that the window has been
scrolled explicitly by the Lisp program. This affects what the next
redisplay does if point is off the screen: instead of scrolling the
window to show the text around point, it moves point to a location that
is on the screen.
frozen_window_start_pstart of this window should not be changed, even if point
gets invisible.
start_at_line_begnil means current value of start was the beginning of a line
when it was chosen.
use_timeget-lru-window uses this field.
sequence_numberlast_modifiedmodiff field of the window's buffer, as of the last time
a redisplay completed in this window.
last_overlay_modifiedoverlay_modiff field of the window's buffer, as of the last
time a redisplay completed in this window.
last_pointlast_had_starnil value means the window's buffer was modified when the
window was last updated.
vertical_scroll_barleft_margin_colsright_margin_colsnil means no margin.
left_fringe_widthright_fringe_widthnil or t means use the values of the frame.
fringes_outside_marginsnil value means the fringes outside the display margins;
othersize they are between the margin and the text.
window_end_posz minus the buffer position of the last glyph
in the current matrix of the window. The value is only valid if
window_end_valid is not nil.
window_end_byteposwindow_end_pos.
window_end_vposwindow_end_pos.
window_end_validnil value if window_end_pos is truly
valid. This is nil if nontrivial redisplay is pre-empted, since in that
case the display that window_end_pos was computed for did not get
onto the screen.
cursorlast_cursorcursor as of the last redisplay that finished.
phys_cursorphys_cursor_typephys_cursor_heightphys_cursor_widthphys_cursor_on_pcursor_off_plast_cursor_off_pcursor_off_p as of the time of
the last redisplay.
must_be_updated_phscrollvscrolldedicatednil if this window is dedicated to its buffer.
display_tablenil if none is specified for it.
update_mode_linenil means this window's mode line needs to be updated.
base_line_numbernil.
This is used for displaying the line number of point in the mode line.
base_line_posnil meaning none is known. If it is a buffer, don't display
the line number as long as the window shows that buffer.
column_number_displayednil
if column numbers are not being displayed.
current_matrixdesired_matrix
The fields of a process (for a complete list, see the definition of
struct Lisp_Process in process.h) include:
namecommandnil if the
process is running or t if the process is stopped.
filtersentinelbufferpidchildpt if this is really a child process. For a network or
serial connection, it is a plist based on the arguments to
make-network-process or make-serial-process.
markkill_without_queryraw_statuswait system call.
statusprocess-status should return it.
tickupdate_tickpty_flagnil if communication with the subprocess uses a pty;
nil if it uses a pipe.
infdoutfdtty_namenil if it is using pipes.
decode_coding_systemdecoding_bufdecoding_carryoverencode_coding_systemencoding_bufinherit_coding_system_flagcoding-system of the process buffer from the
coding system used to decode process output.
typereal, network,
serial.
Here are some guidelines for use of integer types in the Emacs C source code. These guidelines sometimes give competing advice; common sense is advised.
int len = strlen
(s); unless the length of s is required for other reasons to
fit in int range.
size_t instead of ptrdiff_t, or uintptr_t instead
of intptr_t).
int for Emacs character codes, in the range 0 .. 0x3FFFFF.
More generally, prefer int for integers known to be in
int range, e.g., screen column counts.
ptrdiff_t for sizes, i.e., for integers bounded by the
maximum size of any individual C object or by the maximum number of
elements in any C array. This is part of Emacs's general preference
for signed types. Using ptrdiff_t limits objects to
PTRDIFF_MAX bytes, but larger objects would cause trouble
anyway since they would break pointer subtraction, so this does not
impose an arbitrary limit.
ssize_t except when communicating to low-level APIs that
have ssize_t-related limitations. Although it's equivalent to
ptrdiff_t on typical platforms, ssize_t is occasionally
narrower, so using it for size-related calculations could overflow.
Also, ptrdiff_t is more ubiquitous and better-standardized, has
standard printf formats, and is the basis for Emacs's internal
size-overflow checking. When using ssize_t, please note that
POSIX requires support only for values in the range −1 ..
SSIZE_MAX.
intptr_t for internal representations of pointers, or
for integers bounded only by the number of objects that can exist at
any given time or by the total number of bytes that can be allocated.
Currently Emacs sometimes uses other types when intptr_t would
be better; fixing this is lower priority, as the code works as-is on
Emacs's current porting targets.
EMACS_INT for representing values
converted to or from Emacs Lisp fixnums, as fixnum arithmetic is based
on EMACS_INT.
off_t, time_t). Do not assume that a system type is
signed, unless this assumption is known to be safe. For example,
although off_t is always signed, time_t need not be.
printmax_t for representing
values that might be any signed integer that can be printed,
using a printf-family function.
intmax_t for representing values that might be any
signed integer value.
bool, false and true for booleans.
Using bool can make programs easier to read and a bit faster than
using int. Although it is also OK to use int, 0
and 1, this older style is gradually being phased out. When
using bool, respect the limitations of the replacement
implementation of bool, as documented in the source file
lib/stdbool.in.h. In particular, boolean bitfields should be of type
bool_bf, not bool, so that they work correctly even when
compiling Objective C with standard GCC.
unsigned int or signed int to
int, as int is less portable: it might be signed, and
might not be. Single-bit bit fields should be unsigned int or
bool_bf so that their values are 0 or 1.
Here is a list of the more important error symbols in standard Emacs, grouped by concept. The list includes each symbol's message and a cross reference to a description of how the error can occur.
Each error symbol has an set of parent error conditions that is a
list of symbols. Normally this list includes the error symbol itself
and the symbol error. Occasionally it includes additional
symbols, which are intermediate classifications, narrower than
error but broader than a single error symbol. For example, all
the errors in accessing files have the condition file-error. If
we do not say here that a certain error symbol has additional error
conditions, that means it has none.
As a special exception, the error symbol quit does not have the
condition error, because quitting is not considered an error.
Most of these error symbols are defined in C (mainly data.c),
but some are defined in Lisp. For example, the file userlock.el
defines the file-locked and file-supersession errors.
Several of the specialized Lisp libraries distributed with Emacs
define their own error symbols. We do not attempt to list of all
those here.
See Errors, for an explanation of how errors are generated and handled.
errorquitargs-out-of-rangearith-errorbeginning-of-bufferbuffer-read-onlycircular-listcl-assertion-failedcl-assert macro fails a test. See Assertions.
coding-system-errorcyclic-function-indirectioncyclic-variable-indirectiondbus-errorend-of-bufferend-of-filefile-error, because it pertains to the
Lisp reader, not to file I/O. See Input Functions.
file-already-existsfile-error. See Writing to Files.
file-date-errorfile-error. It occurs when
copy-file tries and fails to set the last-modification time of
the output file. See Changing Files.
file-errorfile-error is present. Thus,
the error-strings are not very relevant. However, these error symbols
do have error-message properties, and if no data is provided,
the error-message property is used. See Files.
compression-errorfile-error, which results from
problems handling a compressed file. See How Programs Do Loading.
file-lockedfile-error. See File Locks.
file-supersessionfile-error. See Modification Time.
file-notify-errorfile-error. It happens, when a file
could not be watched for changes. See File Notifications.
ftp-errorfile-error, which results from
problems in accessing a remote file using ftp. See Remote Files.
invalid-functioninvalid-read-syntaxinvalid-regexpmark-inactiveno-catchscan-errorsearch-failedsetting-constantnil, t, and keyword
symbols. See Constant Variables.
text-read-onlybuffer-read-only. See Special Properties.
undefined-coloruser-errorvoid-functionvoid-variablewrong-number-of-argumentswrong-type-argumentIn this section we list some of the more general keymaps. Many of these exist when Emacs is first started, but some are loaded only when the respective feature is accessed.
There are many other, more specialized, maps than these; in particular those associated with major and minor modes. The minibuffer uses several keymaps (see Completion Commands). For more details on keymaps, see Keymaps.
2C-mode-mapabbrev-mapbutton-buffer-mapbutton-mapctl-x-4-mapctl-x-5-mapctl-x-mapctl-x-r-mapesc-mapfacemenu-keymapfunction-key-maplocal-function-key-map (q.v.) instances.
global-mapgoto-maphelp-mapHelper-help-mapinput-decode-mapkey-translation-maplocal-function-key-map. See Translation Keymaps.
kmacro-keymaplocal-function-key-mapmenu-bar-file-menumenu-bar-edit-menumenu-bar-options-menuglobal-buffers-menu-mapmenu-bar-tools-menumenu-bar-help-menumenu-bar-search-menu, etc. See Menu Bar.
minibuffer-inactive-mode-mapmode-line-coding-system-mapmode-line-input-method-mapmode-line-column-line-number-mode-mapmode-specific-mapdisplay-bindings),
where it describes the main use of the C-c prefix key.
mouse-appearance-menu-mapmule-keymapnarrow-mapprog-mode-mapquery-replace-mapmulti-query-replace-mapquery-replace and related
commands; also for y-or-n-p and map-y-or-n-p. The functions
that use this map do not support prefix keys; they look up one event at a
time. multi-query-replace-map extends query-replace-map
for multi-buffer replacements. See query-replace-map.
search-mapspecial-mode-maptool-bar-mapuniversal-argument-mapvc-prefix-mapx-alternatives-mapx-setup-function-keys uses this.
The following is a list of some hook variables that let you provide functions to be called from within Emacs on suitable occasions.
Most of these variables have names ending with `-hook'. They are
normal hooks, run by means of run-hooks. The value of such
a hook is a list of functions; the functions are called with no
arguments and their values are completely ignored. The recommended way
to put a new function on such a hook is to call add-hook.
See Hooks, for more information about using hooks.
The variables whose names end in `-functions' are usually abnormal hooks (some old code may also use the deprecated `-hooks' suffix); their values are lists of functions, but these functions are called in a special way (they are passed arguments, or their return values are used). The variables whose names end in `-function' have single functions as their values.
This is not an exhaustive list, it only covers the more general hooks.
For example, every major mode defines a hook named
`modename-mode-hook'. The major mode command runs this
normal hook with run-mode-hooks as the very last thing it does.
See Mode Hooks. Most minor modes have mode hooks too.
A special feature allows you to specify expressions to evaluate if and when a file is loaded (see Hooks for Loading). That feature is not exactly a hook, but does a similar job.
activate-mark-hookdeactivate-mark-hookafter-change-functionsbefore-change-functionsfirst-change-hookafter-change-major-mode-hookchange-major-mode-after-body-hookafter-init-hookbefore-init-hookemacs-startup-hookwindow-setup-hookafter-insert-file-functionswrite-region-annotate-functionswrite-region-post-annotation-functionafter-make-frame-functionsbefore-make-frame-hookafter-save-hookbefore-save-hookwrite-contents-functionswrite-file-functionsafter-setting-font-hookauto-save-hookbefore-hack-local-variables-hookhack-local-variables-hookbuffer-access-fontify-functionsbuffer-list-update-hookbuffer-quit-functionchange-major-mode-hookcommand-line-functionsdelayed-warnings-hookpost-command-hook (q.v.).
focus-in-hookfocus-out-hookdelete-frame-functionsdelete-terminal-functionspop-up-frame-functionsplit-window-preferred-functionecho-area-clear-hookfind-file-hookfind-file-not-found-functionsfont-lock-extend-after-change-region-functionfont-lock-extend-region-functionsfont-lock-fontify-buffer-functionfont-lock-fontify-region-functionfont-lock-mark-block-functionfont-lock-unfontify-buffer-functionfont-lock-unfontify-region-functionfontification-functionsframe-auto-hide-functionkill-buffer-hookkill-buffer-query-functionskill-emacs-hookkill-emacs-query-functionsmenu-bar-update-hookminibuffer-setup-hookminibuffer-exit-hookmouse-leave-buffer-hookmouse-position-functionprefix-command-echo-keystrokes-functionsnil if there's no
prefix state. See Prefix Command Arguments.
prefix-command-preserve-state-hookpre-redisplay-functionspost-command-hookpre-command-hookpost-gc-hookpost-self-insert-hooksuspend-hooksuspend-resume-hooksuspend-tty-functionsresume-tty-functionssyntax-begin-functionsyntax-propertize-extend-region-functionssyntax-propertize-functionfont-lock-syntactic-face-functiontemp-buffer-setup-hooktemp-buffer-show-functiontemp-buffer-show-hooktty-setup-hookwindow-configuration-change-hookwindow-scroll-functionswindow-size-change-functionswindow-text-change-functions%: Arithmetic Operations
&optional: Argument List
&rest: Argument List
*: Arithmetic Operations
interactive: Using Interactive
+: Arithmetic Operations
, (with backquote): Backquote
,@ (with backquote): Backquote
-: Arithmetic Operations
/: Arithmetic Operations
/=: Comparison of Numbers
1+: Arithmetic Operations
1-: Arithmetic Operations
1value: Test Coverage
2C-mode-map: Prefix Keys
<: Comparison of Numbers
<=: Comparison of Numbers
=: Comparison of Numbers
>: Comparison of Numbers
>=: Comparison of Numbers
interactive: Using Interactive
interactive: Using Interactive
`: Backquote
abbrev-all-caps: Abbrev Expansion
abbrev-expand-function: Abbrev Expansion
abbrev-expansion: Abbrev Expansion
abbrev-file-name: Abbrev Files
abbrev-get: Abbrev Properties
abbrev-insert: Abbrev Expansion
abbrev-map: Standard Keymaps
abbrev-minor-mode-table-alist: Standard Abbrev Tables
abbrev-prefix-mark: Abbrev Expansion
abbrev-put: Abbrev Properties
abbrev-start-location: Abbrev Expansion
abbrev-start-location-buffer: Abbrev Expansion
abbrev-symbol: Abbrev Expansion
abbrev-table-get: Abbrev Table Properties
abbrev-table-name-list: Abbrev Tables
abbrev-table-p: Abbrev Tables
abbrev-table-put: Abbrev Table Properties
abbreviate-file-name: Directory Names
abbrevs-changed: Abbrev Files
abort-recursive-edit: Recursive Editing
abs: Comparison of Numbers
accept-change-group: Atomic Changes
accept-process-output: Accepting Output
access-file: Testing Accessibility
accessible-keymaps: Scanning Keymaps
acos: Math Functions
action (button property): Button Properties
display-buffer: Choosing Window
display-buffer: Choosing Window
action, customization keyword: Type Keywords
activate-change-group: Atomic Changes
activate-mark-hook: The Mark
active-minibuffer-window: Minibuffer Windows
adaptive-fill-first-line-regexp: Adaptive Fill
adaptive-fill-function: Adaptive Fill
adaptive-fill-mode: Adaptive Fill
adaptive-fill-regexp: Adaptive Fill
add-face-text-property: Changing Properties
add-function: Core Advising Primitives
add-hook: Setting Hooks
add-name-to-file: Changing Files
add-text-properties: Changing Properties
add-to-history: Minibuffer History
add-to-invisibility-spec: Invisible Text
add-to-list: List Variables
add-to-ordered-list: List Variables
adjust-window-trailing-edge: Resizing Windows
advice-add: Advising Named Functions
advice-eval-interactive-spec: Core Advising Primitives
advice-function-mapc: Core Advising Primitives
advice-function-member-p: Core Advising Primitives
advice-mapc: Advising Named Functions
advice-member-p: Advising Named Functions
advice-remove: Advising Named Functions
after-change-functions: Change Hooks
after-change-major-mode-hook: Mode Hooks
after-find-file: Subroutines of Visiting
after-init-hook: Init File
after-init-time: Startup Summary
after-insert-file-functions: Format Conversion Piecemeal
after-load-functions: Hooks for Loading
after-make-frame-functions: Creating Frames
after-revert-hook: Reverting
after-save-hook: Saving Buffers
after-setting-font-hook: Standard Hooks
after-string (overlay property): Overlay Properties
alist-get: Association Lists
all-completions: Basic Completion
alpha, a frame parameter: Font and Color Parameters
and: Combining Conditions
append: Building Lists
append-to-file: Writing to Files
apply: Calling Functions
apply, and debugging: Internals of Debugger
apply-partially: Calling Functions
apropos: Help Functions
aref: Array Functions
args, customization keyword: Composite Types
argv: Command-Line Arguments
arith-error example: Handling Errors
arith-error in division: Arithmetic Operations
arrayp: Array Functions
ascii-case-table: Case Tables
aset: Array Functions
ash: Bitwise Operations
asin: Math Functions
ask-user-about-lock: File Locks
ask-user-about-supersession-threat: Modification Time
assoc: Association Lists
assoc-default: Association Lists
assoc-string: Text Comparison
assq: Association Lists
assq-delete-all: Association Lists
atan: Math Functions
atom: List-related Predicates
auto-coding-alist: Default Coding Systems
auto-coding-functions: Default Coding Systems
auto-coding-regexp-alist: Default Coding Systems
auto-fill-chars: Auto Filling
auto-fill-function: Auto Filling
auto-hscroll-mode: Horizontal Scrolling
auto-lower, a frame parameter: Management Parameters
auto-mode-alist: Auto Major Mode
auto-raise, a frame parameter: Management Parameters
auto-raise-tool-bar-buttons: Tool Bar
auto-resize-tool-bars: Tool Bar
auto-save-default: Auto-Saving
auto-save-file-name-p: Auto-Saving
auto-save-hook: Auto-Saving
auto-save-interval: Auto-Saving
auto-save-list-file-name: Auto-Saving
auto-save-list-file-prefix: Auto-Saving
auto-save-mode: Auto-Saving
auto-save-timeout: Auto-Saving
auto-save-visited-file-name: Auto-Saving
auto-window-vscroll: Vertical Scrolling
autoload: Autoload
autoload-do-load: Autoload
autoloadp: Autoload
back-to-indentation: Motion by Indent
background-color, a frame parameter: Font and Color Parameters
background-mode, a frame parameter: Font and Color Parameters
backtrace: Internals of Debugger
backtrace-debug: Internals of Debugger
backtrace-frame: Internals of Debugger
backup-buffer: Making Backups
backup-by-copying: Rename or Copy
backup-by-copying-when-linked: Rename or Copy
backup-by-copying-when-mismatch: Rename or Copy
backup-by-copying-when-privileged-mismatch: Rename or Copy
backup-directory-alist: Making Backups
backup-enable-predicate: Making Backups
backup-file-name-p: Backup Names
backup-inhibited: Making Backups
backward-button: Button Buffer Commands
backward-char: Character Motion
backward-delete-char-untabify: Deletion
backward-delete-char-untabify-method: Deletion
backward-list: List Motion
backward-prefix-chars: Motion and Syntax
backward-sexp: List Motion
backward-to-indentation: Motion by Indent
backward-up-list: List Motion
backward-word: Word Motion
backward-word-strictly: Word Motion
balance-windows: Resizing Windows
balance-windows-area: Resizing Windows
barf-if-buffer-read-only: Read Only Buffers
base64-decode-region: Base 64
base64-decode-string: Base 64
base64-encode-region: Base 64
base64-encode-string: Base 64
batch-byte-compile: Compilation Functions
baud-rate: Terminal Output
beep: Beeping
before-change-functions: Change Hooks
before-hack-local-variables-hook: File Local Variables
before-init-hook: Init File
before-init-time: Startup Summary
before-make-frame-hook: Creating Frames
before-revert-hook: Reverting
before-save-hook: Saving Buffers
before-string (overlay property): Overlay Properties
beginning-of-buffer: Buffer End Motion
beginning-of-defun: List Motion
beginning-of-defun-function: List Motion
beginning-of-line: Text Lines
bidi-display-reordering: Bidirectional Display
bidi-find-overridden-directionality: Bidirectional Display
bidi-paragraph-direction: Bidirectional Display
bidi-string-mark-left-to-right: Bidirectional Display
binary coding system: Coding System Basics
bindat-get-field: Bindat Functions
bindat-ip-to-string: Bindat Functions
bindat-length: Bindat Functions
bindat-pack: Bindat Functions
bindat-unpack: Bindat Functions
bitmap-spec-p: Face Attributes
blink-cursor-alist: Cursor Parameters
blink-matching-delay: Blinking
blink-matching-open: Blinking
blink-matching-paren: Blinking
blink-matching-paren-distance: Blinking
blink-paren-function: Blinking
bobp: Near Point
bolp: Near Point
bool-vector: Bool-Vectors
bool-vector-count-consecutive: Bool-Vectors
bool-vector-count-population: Bool-Vectors
bool-vector-exclusive-or: Bool-Vectors
bool-vector-intersection: Bool-Vectors
bool-vector-not: Bool-Vectors
bool-vector-p: Bool-Vectors
bool-vector-set-difference: Bool-Vectors
bool-vector-subsetp: Bool-Vectors
bool-vector-union: Bool-Vectors
booleanp: nil and t
border-color, a frame parameter: Font and Color Parameters
border-width, a frame parameter: Layout Parameters
bottom-divider-width, a frame parameter: Layout Parameters
boundp: Void Variables
buffer-access-fontified-property: Lazy Properties
buffer-access-fontify-functions: Lazy Properties
buffer-auto-save-file-format: Format Conversion Round-Trip
buffer-auto-save-file-name: Auto-Saving
buffer-backed-up: Making Backups
buffer-base-buffer: Indirect Buffers
buffer-chars-modified-tick: Buffer Modification
buffer-disable-undo: Maintaining Undo
buffer-display-count: Buffers and Windows
buffer-display-table: Active Display Table
buffer-display-time: Buffers and Windows
buffer-enable-undo: Maintaining Undo
buffer-end: Point
buffer-file-coding-system: Encoding and I/O
buffer-file-format: Format Conversion Round-Trip
buffer-file-name: Buffer File Name
buffer-file-number: Buffer File Name
buffer-file-truename: Buffer File Name
buffer-invisibility-spec: Invisible Text
buffer-list: Buffer List
buffer-list, a frame parameter: Buffer Parameters
buffer-list-update-hook: Standard Hooks
buffer-list-update-hook: Buffer List
buffer-live-p: Killing Buffers
buffer-local-value: Creating Buffer-Local
buffer-local-variables: Creating Buffer-Local
buffer-modified-p: Buffer Modification
buffer-modified-tick: Buffer Modification
buffer-name: Buffer Names
buffer-name-history: Minibuffer History
buffer-narrowed-p: Narrowing
buffer-offer-save: Killing Buffers
buffer-predicate, a frame parameter: Buffer Parameters
buffer-quit-function: Standard Hooks
buffer-read-only: Read Only Buffers
buffer-save-without-query: Killing Buffers
buffer-saved-size: Auto-Saving
buffer-size: Point
buffer-stale-function: Reverting
buffer-string: Buffer Contents
buffer-substring: Buffer Contents
buffer-substring-filters: Buffer Contents
buffer-substring-no-properties: Buffer Contents
buffer-substring-with-bidi-context: Bidirectional Display
buffer-swap-text: Swapping Text
buffer-undo-list: Undo
bufferp: Buffer Basics
bufferpos-to-filepos: Text Representations
bury-buffer: Buffer List
butlast: List Elements
button (button property): Button Properties
button-activate: Manipulating Buttons
button-at: Manipulating Buttons
button-end: Manipulating Buttons
button-face, customization keyword: Type Keywords
button-get: Manipulating Buttons
button-has-type-p: Manipulating Buttons
button-label: Manipulating Buttons
button-prefix, customization keyword: Type Keywords
button-put: Manipulating Buttons
button-start: Manipulating Buttons
button-suffix, customization keyword: Type Keywords
button-type: Manipulating Buttons
button-type-get: Manipulating Buttons
button-type-put: Manipulating Buttons
button-type-subtype-p: Manipulating Buttons
byte-boolean-vars: Writing Emacs Primitives
byte-boolean-vars: Variables with Restricted Values
byte-code-function-p: What Is a Function
byte-compile: Compilation Functions
byte-compile-dynamic: Dynamic Loading
byte-compile-dynamic-docstrings: Docs and Compilation
byte-compile-file: Compilation Functions
require: Named Features
byte-recompile-directory: Compilation Functions
byte-to-position: Text Representations
byte-to-string: Converting Representations
C-M-x: Instrumenting
C-x C-a C-m: Edebug Execution Modes
C-x X =: Coverage Testing
caar: List Elements
cadr: List Elements
call-interactively: Interactive Call
call-process: Synchronous Processes
call-process, command-line arguments from minibuffer: Shell Arguments
call-process-region: Synchronous Processes
call-process-shell-command: Synchronous Processes
called-interactively-p: Distinguish Interactive
cancel-change-group: Atomic Changes
cancel-debug-on-entry: Function Debugging
cancel-timer: Timers
capitalize: Case Conversion
capitalize-region: Case Changes
capitalize-word: Case Changes
car: List Elements
car-safe: List Elements
case-fold-search: Searching and Case
case-replace: Searching and Case
case-table-p: Case Tables
catch: Catch and Throw
category (overlay property): Overlay Properties
category (text property): Special Properties
category-docstring: Categories
category-set-mnemonics: Categories
category-table: Categories
category-table-p: Categories
cdar: List Elements
cddr: List Elements
cdr: List Elements
cdr-safe: List Elements
ceiling: Numeric Conversions
load-path at configure time: Building Emacs
change-major-mode-after-body-hook: Mode Hooks
change-major-mode-hook: Creating Buffer-Local
char-after: Near Point
char-before: Near Point
char-category-set: Categories
char-charset: Character Sets
char-code-property-description: Character Properties
char-displayable-p: Fontsets
char-equal: Text Comparison
char-or-string-p: Predicates for Strings
char-property-alias-alist: Examining Properties
char-script-table: Character Properties
char-syntax: Syntax Table Functions
char-table-extra-slot: Char-Tables
char-table-p: Char-Tables
char-table-parent: Char-Tables
char-table-range: Char-Tables
char-table-subtype: Char-Tables
char-to-string: String Conversion
char-width: Size of Displayed Text
char-width-table: Character Properties
characterp: Character Codes
charset, text property: Explicit Encoding
charset-after: Scanning Charsets
charset-list: Character Sets
charset-plist: Character Sets
charset-priority-list: Character Sets
charsetp: Character Sets
check-coding-system: Lisp and Coding Systems
check-coding-systems-region: Lisp and Coding Systems
checkdoc: Tips
checkdoc-current-buffer: Tips
checkdoc-file: Tips
checkdoc-minor-mode: Documentation Tips
checkdoc-package-keywords: Library Headers
checkdoc-package-keywords-flag: Library Headers
cl: Lisp History
eq: Comparison of Numbers
union, intersection: Sets And Lists
setf functions: Adding Generalized Variables
throw in Emacs: Catch and Throw
rplaca vs setcar: Modifying Lists
cl-call-next-method: Generic Functions
cl-defgeneric: Generic Functions
cl-defmethod: Generic Functions
cl-next-method-p: Generic Functions
clear-abbrev-table: Abbrev Tables
clear-image-cache: Image Cache
clear-string: Modifying Strings
clear-this-command-keys: Command Loop Info
clear-visited-file-modtime: Modification Time
clone-indirect-buffer: Indirect Buffers
clrhash: Hash Access
coding-system-aliases: Coding System Basics
coding-system-change-eol-conversion: Lisp and Coding Systems
coding-system-change-text-conversion: Lisp and Coding Systems
coding-system-charset-list: Lisp and Coding Systems
coding-system-eol-type: Lisp and Coding Systems
coding-system-for-read: Specifying Coding Systems
coding-system-for-write: Specifying Coding Systems
coding-system-get: Coding System Basics
coding-system-list: Lisp and Coding Systems
coding-system-p: Lisp and Coding Systems
coding-system-priority-list: Specifying Coding Systems
collapse-delayed-warnings: Delayed Warnings
color-defined-p: Color Names
color-gray-p: Color Names
color-supported-p: Color Names
color-values: Color Names
combine-after-change-calls: Change Hooks
combine-and-quote-strings: Shell Arguments
command-debug-status: Internals of Debugger
command-error-function: Processing of Errors
command-execute: Interactive Call
command-history: Command History
command-line: Command-Line Arguments
command-line-args: Command-Line Arguments
command-line-args-left: Command-Line Arguments
command-line-functions: Command-Line Arguments
command-line-processed: Command-Line Arguments
command-remapping: Remapping Commands
command-switch-alist: Command-Line Arguments
commandp: Interactive Call
commandp example: High-Level Completion
comment-end-can-be-escaped: Control Parsing
compare-buffer-substrings: Comparing Text
compare-strings: Text Comparison
compare-window-configurations: Window Configurations
compile-defun: Compilation Functions
completing-read: Minibuffer Completion
completing-read-function: Minibuffer Completion
completion-at-point: Completion in Buffers
completion-at-point-functions: Completion in Buffers
completion-auto-help: Completion Commands
completion-boundaries: Basic Completion
completion-category-overrides: Completion Variables
completion-extra-properties: Completion Variables
completion-ignore-case: Basic Completion
completion-ignored-extensions: File Name Completion
completion-in-region: Completion in Buffers
completion-regexp-list: Basic Completion
completion-styles: Completion Variables
completion-styles-alist: Completion Variables
completion-table-case-fold: Basic Completion
completion-table-dynamic: Programmed Completion
completion-table-in-turn: Basic Completion
completion-table-merge: Basic Completion
completion-table-subvert: Basic Completion
completion-table-with-cache: Programmed Completion
completion-table-with-predicate: Basic Completion
completion-table-with-quoting: Basic Completion
completion-table-with-terminator: Basic Completion
composition (text property): Special Properties
composition property, and point display: Adjusting Point
compute-motion: Screen Lines
concat: Creating Strings
cond: Conditionals
condition-case: Handling Errors
condition-case-unless-debug: Handling Errors
cons: Building Lists
cons-cells-consed: Memory Usage
consp: List-related Predicates
constrain-to-field: Fields
continue-process: Signals to Processes
Control-X-prefix: Prefix Keys
controlling-tty-p: Suspending Emacs
convert-standard-filename: Standard File Names
coordinates-in-window-p: Coordinates and Windows
copy-abbrev-table: Abbrev Tables
copy-alist: Association Lists
copy-category-table: Categories
copy-directory: Create/Delete Dirs
copy-file: Changing Files
copy-hash-table: Other Hash
copy-keymap: Creating Keymaps
copy-marker: Creating Markers
copy-overlay: Managing Overlays
copy-region-as-kill: Kill Functions
copy-sequence: Sequence Functions
copy-syntax-table: Syntax Table Functions
copy-tree: Building Lists
copysign: Float Basics
cos: Math Functions
count-lines: Text Lines
count-loop: A Sample Function Description
count-screen-lines: Screen Lines
count-words: Text Lines
create-file-buffer: Subroutines of Visiting
create-fontset-from-fontset-spec: Fontsets
create-image: Defining Images
create-lockfiles: File Locks
ctl-arrow: Usual Display
ctl-x-4-map: Prefix Keys
ctl-x-5-map: Prefix Keys
ctl-x-map: Prefix Keys
ctl-x-r-map: Standard Keymaps
current-active-maps: Active Keymaps
current-bidi-paragraph-direction: Bidirectional Display
current-buffer: Current Buffer
current-case-table: Case Tables
current-column: Columns
current-fill-column: Margins
current-frame-configuration: Frame Configurations
current-global-map: Controlling Active Maps
current-idle-time: Idle Timers
current-indentation: Primitive Indent
current-input-method: Input Methods
current-input-mode: Input Modes
current-justification: Filling
current-kill: Low-Level Kill Ring
current-left-margin: Margins
current-local-map: Controlling Active Maps
current-message: Displaying Messages
current-minor-mode-maps: Controlling Active Maps
current-prefix-arg: Prefix Command Arguments
current-time: Time of Day
current-time-string: Time of Day
current-time-zone: Time Zone Rules
current-window-configuration: Window Configurations
current-word: Buffer Contents
cursor (text property): Special Properties
display properties and overlays: Special Properties
cursor-color, a frame parameter: Font and Color Parameters
cursor-in-echo-area: Echo Area Customization
cursor-in-non-selected-windows: Cursor Parameters
cursor-intangible (text property): Special Properties
cursor-intangible-mode: Special Properties
cursor-sensor-functions (text property): Special Properties
cursor-sensor-mode: Special Properties
cursor-type: Cursor Parameters
cursor-type, a frame parameter: Cursor Parameters
cust-print: Printing in Edebug
custom-add-frequent-value: Variable Definitions
custom-initialize-delay: Building Emacs
custom-known-themes: Custom Themes
custom-reevaluate-setting: Variable Definitions
custom-set-faces: Applying Customizations
custom-set-variables: Applying Customizations
custom-theme-p: Custom Themes
custom-theme-set-faces: Custom Themes
custom-theme-set-variables: Custom Themes
custom-unlispify-remove-prefixes: Group Definitions
custom-variable-p: Variable Definitions
customize-package-emacs-version-alist: Common Keywords
cygwin-convert-file-name-from-windows: File Names
cygwin-convert-file-name-to-windows: File Names
data-directory: Help Functions
date-leap-year-p: Time Calculations
date-to-time: Time Parsing
deactivate-mark: The Mark
deactivate-mark-hook: The Mark
debug: Invoking the Debugger
debug-ignored-errors: Error Debugging
debug-on-entry: Function Debugging
debug-on-error: Error Debugging
debug-on-error use: Processing of Errors
debug-on-event: Error Debugging
debug-on-message: Error Debugging
debug-on-next-call: Internals of Debugger
debug-on-quit: Infinite Loops
debug-on-signal: Error Debugging
debugger: Internals of Debugger
debugger-bury-or-kill: Using Debugger
declare: Declare Form
declare-function: Declaring Functions
decode-char: Character Sets
decode-coding-inserted-region: Explicit Encoding
decode-coding-region: Explicit Encoding
decode-coding-string: Explicit Encoding
decode-time: Time Conversion
def-edebug-spec: Instrumenting Macro Calls
defalias: Defining Functions
default-boundp: Default Value
default-directory: File Name Expansion
default-file-modes: Changing Files
default-font-height: Low-Level Font
default-font-width: Low-Level Font
default-frame-alist: Initial Parameters
default-input-method: Input Methods
default-justification: Filling
default-minibuffer-frame: Minibuffers and Frames
default-process-coding-system: Default Coding Systems
default-text-properties: Examining Properties
default-value: Default Value
defconst: Defining Variables
defcustom: Variable Definitions
defface: Defining Faces
defgroup: Group Definitions
defimage: Defining Images
define-abbrev: Defining Abbrevs
define-abbrev-table: Abbrev Tables
define-advice: Advising Named Functions
define-alternatives: Generic Commands
define-button-type: Button Types
define-category: Categories
define-derived-mode: Derived Modes
define-error: Error Symbols
define-fringe-bitmap: Customizing Bitmaps
define-generic-mode: Generic Modes
define-globalized-minor-mode: Defining Minor Modes
define-hash-table-test: Defining Hash
define-inline: Defining Functions
define-key: Changing Key Bindings
define-key-after: Modifying Menus
define-minor-mode: Defining Minor Modes
define-obsolete-face-alias: Face Functions
define-obsolete-function-alias: Obsolete Functions
define-obsolete-variable-alias: Variable Aliases
define-package: Multi-file Packages
define-prefix-command: Prefix Keys
defined-colors: Color Names
defining-kbd-macro: Keyboard Macros
defmacro: Defining Macros
defsubr, Lisp symbol for a primitive: Writing Emacs Primitives
defsubst: Inline Functions
deftheme: Custom Themes
defun: Defining Functions
DEFUN, C macro to define Lisp primitives: Writing Emacs Primitives
defun-prompt-regexp: List Motion
defvar: Defining Variables
defvar-local: Creating Buffer-Local
DEFVAR_INT, DEFVAR_LISP, DEFVAR_BOOL: Writing Emacs Primitives
defvaralias: Variable Aliases
delay-mode-hooks: Mode Hooks
delayed-warnings-hook: Standard Hooks
delayed-warnings-hook: Delayed Warnings
delayed-warnings-list: Delayed Warnings
delete: Sets And Lists
delete-and-extract-region: Deletion
delete-auto-save-file-if-necessary: Auto-Saving
delete-auto-save-files: Auto-Saving
delete-backward-char: Deletion
delete-blank-lines: User-Level Deletion
delete-by-moving-to-trash: Changing Files
delete-by-moving-to-trash: Create/Delete Dirs
delete-char: Deletion
delete-directory: Create/Delete Dirs
delete-dups: Sets And Lists
delete-exited-processes: Deleting Processes
delete-field: Fields
delete-file: Changing Files
delete-frame: Deleting Frames
delete-frame event: Misc Events
delete-frame-functions: Deleting Frames
delete-horizontal-space: User-Level Deletion
delete-indentation: User-Level Deletion
delete-minibuffer-contents: Minibuffer Contents
delete-old-versions: Numbered Backups
delete-other-windows: Deleting Windows
delete-overlay: Managing Overlays
delete-process: Deleting Processes
delete-region: Deletion
delete-selection, symbol property: The Mark
delete-selection-helper: The Mark
delete-selection-pre-hook: The Mark
delete-terminal: Multiple Terminals
delete-terminal-functions: Multiple Terminals
delete-to-left-margin: Margins
delete-trailing-whitespace: User-Level Deletion
delete-window: Deleting Windows
delete-windows-on: Deleting Windows
delq: Sets And Lists
derived-mode-p: Derived Modes
describe-bindings: Scanning Keymaps
describe-buffer-case-table: Case Tables
describe-categories: Categories
describe-current-display-table: Display Tables
describe-display-table: Display Tables
describe-mode: Mode Help
describe-prefix-bindings: Help Functions
describe-syntax: Syntax Table Functions
desktop-buffer-mode-handlers: Desktop Save Mode
desktop-save-buffer: Desktop Save Mode
destroy-fringe-bitmap: Customizing Bitmaps
detect-coding-region: Lisp and Coding Systems
detect-coding-string: Lisp and Coding Systems
digit-argument: Prefix Command Arguments
ding: Beeping
dir-locals-class-alist: Directory Local Variables
dir-locals-directory-cache: Directory Local Variables
dir-locals-file: Directory Local Variables
dir-locals-set-class-variables: Directory Local Variables
dir-locals-set-directory-class: Directory Local Variables
directory-file-name: Directory Names
directory-files: Contents of Directories
directory-files-and-attributes: Contents of Directories
directory-files-recursively: Contents of Directories
directory-name-p: Directory Names
dired-kept-versions: Numbered Backups
disable-command: Disabling Commands
disable-point-adjustment: Adjusting Point
disable-theme: Custom Themes
disabled: Disabling Commands
disabled-command-function: Disabling Commands
disassemble: Disassembly
discard-input: Event Input Misc
display (overlay property): Overlay Properties
display (text property): Display Property
display property, and point display: Adjusting Point
display, a frame parameter: Basic Parameters
display-backing-store: Display Feature Testing
display-buffer: Choosing Window
display-buffer-alist: Choosing Window
display-buffer-at-bottom: Display Action Functions
display-buffer-base-action: Choosing Window
display-buffer-below-selected: Display Action Functions
display-buffer-fallback-action: Choosing Window
display-buffer-in-previous-window: Display Action Functions
display-buffer-no-window: Display Action Functions
display-buffer-overriding-action: Choosing Window
display-buffer-pop-up-frame: Display Action Functions
display-buffer-pop-up-window: Display Action Functions
display-buffer-reuse-window: Display Action Functions
display-buffer-same-window: Display Action Functions
display-buffer-use-some-frame: Display Action Functions
display-buffer-use-some-window: Display Action Functions
display-color-cells: Display Feature Testing
display-color-p: Display Feature Testing
display-completion-list: Completion Commands
display-delayed-warnings: Delayed Warnings
display-graphic-p: Display Feature Testing
display-grayscale-p: Display Feature Testing
display-images-p: Display Feature Testing
display-message-or-buffer: Displaying Messages
display-mm-dimensions-alist: Display Feature Testing
display-mm-height: Display Feature Testing
display-mm-width: Display Feature Testing
display-monitor-attributes-list: Multiple Terminals
display-mouse-p: Display Feature Testing
display-pixel-height: Display Feature Testing
display-pixel-width: Display Feature Testing
display-planes: Display Feature Testing
display-popup-menus-p: Display Feature Testing
display-save-under: Display Feature Testing
display-screens: Display Feature Testing
display-selections-p: Display Feature Testing
display-supports-face-attributes-p: Display Feature Testing
display-table-slot: Display Tables
display-type, a frame parameter: Basic Parameters
display-visual-class: Display Feature Testing
display-warning: Warning Basics
dnd-protocol-alist: Drag and Drop
do-auto-save: Auto-Saving
doc, customization keyword: Type Keywords
doc-directory: Accessing Documentation
documentation: Accessing Documentation
documentation-property: Accessing Documentation
dolist: Iteration
dom-node: Document Object Model
dotimes: Iteration
dotimes-with-progress-reporter: Progress
double-click-fuzz: Repeat Events
double-click-time: Repeat Events
down-list: List Motion
downcase: Case Conversion
downcase-region: Case Changes
downcase-word: Case Changes
lookup-key: Key Sequence Input
drag-n-drop event: Misc Events
dump-emacs: Building Emacs
dynamic-library-alist: Dynamic Libraries
easy-menu-define: Easy Menu
easy-mmode-define-minor-mode: Defining Minor Modes
echo-area-clear-hook: Echo Area Customization
echo-keystrokes: Echo Area Customization
edebug: Source Breakpoints
edebug-all-defs: Edebug Options
edebug-all-forms: Edebug Options
edebug-continue-kbd-macro: Edebug Options
edebug-defun: Instrumenting
edebug-display-freq-count: Coverage Testing
edebug-eval-macro-args: Instrumenting Macro Calls
edebug-eval-top-level-form: Instrumenting
edebug-global-break-condition: Edebug Options
edebug-initial-mode: Edebug Options
edebug-on-error: Edebug Options
edebug-on-quit: Edebug Options
edebug-print-circle: Printing in Edebug
edebug-print-length: Printing in Edebug
edebug-print-level: Printing in Edebug
edebug-print-trace-after: Trace Buffer
edebug-print-trace-before: Trace Buffer
edebug-save-displayed-buffer-points: Edebug Options
edebug-save-windows: Edebug Options
edebug-set-global-break-condition: Global Break Condition
edebug-set-initial-mode: Edebug Execution Modes
edebug-setup-hook: Edebug Options
edebug-sit-for-seconds: Edebug Execution Modes
edebug-temp-display-freq-count: Coverage Testing
edebug-test-coverage: Edebug Options
edebug-trace: Trace Buffer
edebug-trace: Edebug Options
edebug-tracing: Trace Buffer
edebug-unwrap-results: Edebug Options
edit-and-eval-command: Object from Minibuffer
eight-bit, a charset: Character Sets
electric-future-map: A Sample Variable Description
elt: Sequence Functions
emacs, a charset: Character Sets
emacs-build-time: Version Info
emacs-init-time: Processor Run Time
emacs-internal coding system: Coding System Basics
emacs-lisp-docstring-fill-column: Documentation Tips
emacs-major-version: Version Info
emacs-minor-version: Version Info
emacs-pid: System Environment
emacs-save-session-functions: Session Management
emacs-session-restore: Session Management
emacs-startup-hook: Init File
emacs-uptime: Processor Run Time
emacs-version: Version Info
emacs_module_init: Dynamic Modules
emulation-mode-map-alists: Controlling Active Maps
enable-command: Disabling Commands
enable-dir-local-variables: Directory Local Variables
enable-local-eval: File Local Variables
enable-local-variables: File Local Variables
enable-multibyte-characters: Text Representations
enable-multibyte-characters: Disabling Multibyte
enable-recursive-minibuffers: Recursive Mini
enable-theme: Custom Themes
encode-char: Character Sets
encode-coding-region: Explicit Encoding
encode-coding-string: Explicit Encoding
encode-time: Time Conversion
end-of-buffer: Buffer End Motion
end-of-defun: List Motion
end-of-defun-function: List Motion
end-of-file: Input Functions
end-of-line: Text Lines
eobp: Near Point
eolp: Near Point
eq: Equality Predicates
eql: Comparison of Numbers
equal: Equality Predicates
equal-including-properties: Equality Predicates
erase-buffer: Deletion
error: Signaling Errors
error in debug: Invoking the Debugger
error-conditions: Error Symbols
error-message-string: Handling Errors
esc-map: Prefix Keys
ESC-prefix: Prefix Keys
eval: Eval
eval, and debugging: Internals of Debugger
eval-and-compile: Eval During Compile
eval-buffer: Eval
eval-buffer (Edebug): Instrumenting
eval-current-buffer: Eval
eval-current-buffer (Edebug): Instrumenting
eval-defun (Edebug): Instrumenting
eval-expression (Edebug): Instrumenting
eval-expression-debug-on-error: Error Debugging
eval-expression-print-length: Output Variables
eval-expression-print-level: Output Variables
eval-minibuffer: Object from Minibuffer
eval-region: Eval
eval-region (Edebug): Instrumenting
eval-when-compile: Eval During Compile
evaporate (overlay property): Overlay Properties
even-window-sizes: Choosing Window Options
event-basic-type: Classifying Events
event-click-count: Repeat Events
event-convert-list: Classifying Events
event-end: Accessing Mouse
event-modifiers: Classifying Events
event-start: Accessing Mouse
eventp: Input Events
ewoc-buffer: Abstract Display Functions
ewoc-collect: Abstract Display Functions
ewoc-create: Abstract Display Functions
ewoc-data: Abstract Display Functions
ewoc-delete: Abstract Display Functions
ewoc-enter-after: Abstract Display Functions
ewoc-enter-before: Abstract Display Functions
ewoc-enter-first: Abstract Display Functions
ewoc-enter-last: Abstract Display Functions
ewoc-filter: Abstract Display Functions
ewoc-get-hf: Abstract Display Functions
ewoc-goto-next: Abstract Display Functions
ewoc-goto-node: Abstract Display Functions
ewoc-goto-prev: Abstract Display Functions
ewoc-invalidate: Abstract Display Functions
ewoc-locate: Abstract Display Functions
ewoc-location: Abstract Display Functions
ewoc-map: Abstract Display Functions
ewoc-next: Abstract Display Functions
ewoc-nth: Abstract Display Functions
ewoc-prev: Abstract Display Functions
ewoc-refresh: Abstract Display Functions
ewoc-set-data: Abstract Display Functions
ewoc-set-hf: Abstract Display Functions
interactive form: Using Interactive
interactive: Interactive Examples
exec-directory: Subprocess Creation
exec-path: Subprocess Creation
exec-suffixes: Subprocess Creation
executable-find: Locating Files
execute-extended-command: Interactive Call
execute-kbd-macro: Keyboard Macros
executing-kbd-macro: Keyboard Macros
exit: Recursive Editing
exit-minibuffer: Minibuffer Commands
exit-recursive-edit: Recursive Editing
exp: Math Functions
expand-abbrev: Abbrev Expansion
expand-file-name: File Name Expansion
expt: Math Functions
extended-command-history: Minibuffer History
extra-keyboard-modifiers: Event Mod
face (button property): Button Properties
face (overlay property): Overlay Properties
face (text property): Special Properties
face-all-attributes: Attribute Functions
face-attribute: Attribute Functions
face-attribute-relative-p: Attribute Functions
face-background: Attribute Functions
face-bold-p: Attribute Functions
face-differs-from-default-p: Face Functions
face-documentation: Face Functions
face-documentation: Accessing Documentation
face-equal: Face Functions
face-font: Attribute Functions
face-font-family-alternatives: Font Selection
face-font-registry-alternatives: Font Selection
face-font-rescale-alist: Font Selection
face-font-selection-order: Font Selection
face-foreground: Attribute Functions
face-id: Face Functions
face-inverse-video-p: Attribute Functions
face-italic-p: Attribute Functions
face-list: Face Functions
face-name-history: Minibuffer History
face-remap-add-relative: Face Remapping
face-remap-remove-relative: Face Remapping
face-remap-reset-base: Face Remapping
face-remap-set-base: Face Remapping
face-remapping-alist: Face Remapping
face-spec-set: Defining Faces
face-stipple: Attribute Functions
face-underline-p: Attribute Functions
facemenu-keymap: Prefix Keys
facep: Faces
fboundp: Function Cells
fceiling: Rounding Operations
-unload-function: Unloading
featurep: Named Features
features: Named Features
fetch-bytecode: Dynamic Loading
ffloor: Rounding Operations
field (overlay property): Overlay Properties
field (text property): Special Properties
field-beginning: Fields
field-end: Fields
field-string: Fields
field-string-no-properties: Fields
file-accessible-directory-p: Testing Accessibility
file-acl: Extended Attributes
file-already-exists: Changing Files
file-attributes: File Attributes
file-chase-links: Truenames
file-coding-system-alist: Default Coding Systems
file-directory-p: Kinds of Files
file-equal-p: Truenames
file-error: How Programs Do Loading
file-executable-p: Testing Accessibility
file-exists-p: Testing Accessibility
file-expand-wildcards: Contents of Directories
file-extended-attributes: Extended Attributes
file-in-directory-p: Truenames
file-local-copy: Magic File Names
file-local-variables-alist: File Local Variables
file-locked: File Locks
file-locked-p: File Locks
file-modes: Testing Accessibility
file-modes-symbolic-to-number: Changing Files
file-name-absolute-p: Relative File Names
file-name-all-completions: File Name Completion
file-name-as-directory: Directory Names
file-name-base: File Name Components
file-name-coding-system: Encoding and I/O
file-name-completion: File Name Completion
file-name-directory: File Name Components
file-name-extension: File Name Components
file-name-handler-alist: Magic File Names
file-name-history: Minibuffer History
file-name-nondirectory: File Name Components
file-name-sans-extension: File Name Components
file-name-sans-versions: File Name Components
file-newer-than-file-p: File Attributes
file-newest-backup: Backup Names
file-nlinks: File Attributes
file-notify-add-watch: File Notifications
file-notify-rm-watch: File Notifications
file-notify-valid-p: File Notifications
file-ownership-preserved-p: Testing Accessibility
file-precious-flag: Saving Buffers
file-readable-p: Testing Accessibility
file-regular-p: Kinds of Files
file-relative-name: Relative File Names
file-remote-p: Magic File Names
file-selinux-context: Extended Attributes
file-supersession: Modification Time
file-symlink-p: Kinds of Files
file-truename: Truenames
file-writable-p: Testing Accessibility
filepos-to-bufferpos: Text Representations
fill-column: Margins
fill-context-prefix: Adaptive Fill
fill-forward-paragraph-function: Filling
fill-individual-paragraphs: Filling
fill-individual-varying-indent: Filling
fill-nobreak-predicate: Margins
fill-paragraph: Filling
fill-paragraph-function: Filling
fill-prefix: Margins
fill-region: Filling
fill-region-as-paragraph: Filling
fillarray: Array Functions
filter-buffer-substring: Buffer Contents
filter-buffer-substring-function: Buffer Contents
filter-buffer-substring-functions: Buffer Contents
find-auto-coding: Default Coding Systems
find-backup-file-name: Backup Names
find-buffer-visiting: Buffer File Name
find-charset-region: Scanning Charsets
find-charset-string: Scanning Charsets
find-coding-systems-for-charsets: Lisp and Coding Systems
find-coding-systems-region: Lisp and Coding Systems
find-coding-systems-string: Lisp and Coding Systems
find-file: Visiting Functions
find-file-hook: Visiting Functions
find-file-literally: Visiting Functions
find-file-name-handler: Magic File Names
find-file-noselect: Visiting Functions
find-file-not-found-functions: Visiting Functions
find-file-other-window: Visiting Functions
find-file-read-only: Visiting Functions
find-file-wildcards: Visiting Functions
find-font: Low-Level Font
find-image: Defining Images
find-operation-coding-system: Default Coding Systems
find-word-boundary-function-table: Word Motion
first-change-hook: Change Hooks
fit-frame-to-buffer: Resizing Windows
fit-frame-to-buffer-margins: Resizing Windows
fit-frame-to-buffer-sizes: Resizing Windows
fit-window-to-buffer: Resizing Windows
fit-window-to-buffer-horizontally: Resizing Windows
fixup-whitespace: User-Level Deletion
float: Numeric Conversions
float-e: Math Functions
float-output-format: Output Variables
float-pi: Math Functions
float-time: Time of Day
floatp: Predicates on Numbers
floats-consed: Memory Usage
floor: Numeric Conversions
fmakunbound: Function Cells
fn in function's documentation string: Autoload
focus-follows-mouse: Input Focus
focus-in-hook: Standard Hooks
focus-in-hook: Input Focus
focus-out-hook: Input Focus
focus-out-hook: Standard Hooks
follow-link (button property): Button Properties
following-char: Near Point
font, a frame parameter: Font and Color Parameters
font-at: Low-Level Font
font-backend, a frame parameter: Font and Color Parameters
font-face-attributes: Low-Level Font
font-family-list: Face Attributes
font-get: Low-Level Font
font-info: Low-Level Font
font-lock-add-keywords: Customizing Keywords
font-lock-builtin-face: Faces for Font Lock
font-lock-comment-delimiter-face: Faces for Font Lock
font-lock-comment-face: Faces for Font Lock
font-lock-constant-face: Faces for Font Lock
font-lock-defaults: Font Lock Basics
font-lock-doc-face: Faces for Font Lock
font-lock-ensure &optional beg end: Font Lock Basics
font-lock-ensure-function: Other Font Lock Variables
font-lock-extend-after-change-region-function: Region to Refontify
font-lock-extra-managed-props: Other Font Lock Variables
font-lock-face (text property): Special Properties
font-lock-flush &optional beg end: Font Lock Basics
font-lock-flush-function: Other Font Lock Variables
font-lock-fontify-buffer: Font Lock Basics
font-lock-fontify-buffer-function: Other Font Lock Variables
font-lock-fontify-region beg end &optional loudly: Font Lock Basics
font-lock-fontify-region-function: Other Font Lock Variables
font-lock-function-name-face: Faces for Font Lock
font-lock-keyword-face: Faces for Font Lock
font-lock-keywords: Search-based Fontification
font-lock-keywords-case-fold-search: Search-based Fontification
font-lock-keywords-only: Syntactic Font Lock
font-lock-mark-block-function: Other Font Lock Variables
font-lock-multiline: Font Lock Multiline
font-lock-negation-char-face: Faces for Font Lock
font-lock-preprocessor-face: Faces for Font Lock
font-lock-remove-keywords: Customizing Keywords
font-lock-string-face: Faces for Font Lock
font-lock-syntactic-face-function: Syntactic Font Lock
font-lock-syntax-table: Syntactic Font Lock
font-lock-type-face: Faces for Font Lock
font-lock-unfontify-buffer: Font Lock Basics
font-lock-unfontify-buffer-function: Other Font Lock Variables
font-lock-unfontify-region beg end: Font Lock Basics
font-lock-unfontify-region-function: Other Font Lock Variables
font-lock-variable-name-face: Faces for Font Lock
font-lock-warning-face: Faces for Font Lock
font-put: Low-Level Font
font-spec: Low-Level Font
font-xlfd-name: Low-Level Font
fontification-functions: Auto Faces
fontified (text property): Special Properties
fontp: Low-Level Font
foo: A Sample Function Description
for: Argument Evaluation
force-mode-line-update: Mode Line Basics
force-window-update: Forcing Redisplay
foreground-color, a frame parameter: Font and Color Parameters
format: Formatting Strings
format, customization keyword: Type Keywords
format-alist: Format Conversion Round-Trip
format-find-file: Format Conversion Round-Trip
format-insert-file: Format Conversion Round-Trip
format-message: Formatting Strings
format-mode-line: Emulating Mode Line
format-network-address: Misc Network
format-seconds: Time Parsing
format-time-string: Time Parsing
format-write-file: Format Conversion Round-Trip
forward-button: Button Buffer Commands
forward-char: Character Motion
forward-comment: Motion via Parsing
forward-line: Text Lines
forward-list: List Motion
forward-sexp: List Motion
forward-to-indentation: Motion by Indent
forward-word: Word Motion
forward-word-strictly: Word Motion
frame-alpha-lower-limit: Font and Color Parameters
frame-auto-hide-function: Quitting Windows
frame-char-height: Frame Font
frame-char-width: Frame Font
frame-current-scroll-bars: Scroll Bars
frame-edges: Frame Layout
frame-first-window: Windows and Frames
frame-geometry: Frame Layout
frame-height: Size and Position
frame-inherited-parameters: Creating Frames
frame-inhibit-implied-resize: Implied Frame Resizing
frame-list: Finding All Frames
frame-live-p: Deleting Frames
frame-monitor-attributes: Multiple Terminals
frame-parameter: Parameter Access
frame-parameters: Parameter Access
frame-pixel-height: Size and Position
frame-pixel-width: Size and Position
frame-pointer-visible-p: Mouse Position
frame-position: Size and Position
frame-resize-pixelwise: Size and Position
frame-root-window: Windows and Frames
frame-scroll-bar-height: Scroll Bars
frame-scroll-bar-width: Scroll Bars
frame-selected-window: Selecting Windows
frame-terminal: Frames
frame-text-height: Size and Position
frame-text-width: Size and Position
frame-title-format: Frame Titles
frame-visible-p: Visibility of Frames
frame-width: Size and Position
framep: Frames
frexp: Float Basics
fringe-bitmaps-at-pos: Fringe Bitmaps
fringe-cursor-alist: Fringe Cursors
fringe-indicator-alist: Fringe Indicators
fringes-outside-margins: Fringe Size/Pos
fround: Rounding Operations
fset: Function Cells
ftp-login: Cleanups
ftruncate: Rounding Operations
fullscreen, a frame parameter: Size Parameters
fullscreen-restore, a frame parameter: Size Parameters
funcall: Calling Functions
funcall, and debugging: Internals of Debugger
funcall-interactively: Interactive Call
function: Anonymous Functions
function-documentation property: Documentation Basics
function-get: Symbol Plists
function-put: Symbol Plists
functionp: What Is a Function
fundamental-mode: Major Modes
fundamental-mode-abbrev-table: Standard Abbrev Tables
gap-position: Buffer Gap
gap-size: Buffer Gap
garbage-collect: Garbage Collection
garbage-collection-messages: Garbage Collection
gc-cons-percentage: Garbage Collection
gc-cons-threshold: Garbage Collection
gc-elapsed: Garbage Collection
gcs-done: Garbage Collection
generate-autoload-cookie: Autoload
generate-new-buffer: Creating Buffers
generate-new-buffer-name: Buffer Names
generated-autoload-file: Autoload
get: Symbol Plists
get, defcustom keyword: Variable Definitions
get-buffer: Buffer Names
get-buffer-create: Creating Buffers
get-buffer-process: Process Buffers
get-buffer-window: Buffers and Windows
get-buffer-window-list: Buffers and Windows
get-buffer-xwidgets: Xwidgets
get-byte: Character Codes
get-char-code-property: Character Properties
get-char-property: Examining Properties
get-char-property-and-overlay: Examining Properties
get-charset-property: Character Sets
get-device-terminal: Multiple Terminals
get-file-buffer: Buffer File Name
get-internal-run-time: Processor Run Time
get-largest-window: Cyclic Window Ordering
get-load-suffixes: Load Suffixes
get-lru-window: Cyclic Window Ordering
get-mru-window: Cyclic Window Ordering
get-pos-property: Examining Properties
get-process: Process Information
get-register: Registers
get-text-property: Examining Properties
get-unused-category: Categories
get-window-with-predicate: Cyclic Window Ordering
getenv: System Environment
gethash: Hash Access
global-abbrev-table: Standard Abbrev Tables
global-buffers-menu-map: Standard Keymaps
global-disable-point-adjustment: Adjusting Point
global-key-binding: Functions for Key Lookup
global-map: Controlling Active Maps
global-mode-string: Mode Line Variables
global-set-key: Key Binding Commands
global-unset-key: Key Binding Commands
glyph-char: Glyphs
glyph-face: Glyphs
glyph-table: Glyphs
glyphless-char-display: Glyphless Chars
glyphless-char-display-control: Glyphless Chars
goto-char: Character Motion
goto-map: Prefix Keys
group, customization keyword: Common Keywords
group-gid: User Identification
group-real-gid: User Identification
gui-get-selection: Window System Selections
gui-set-selection: Window System Selections
gv-define-expander: Adding Generalized Variables
gv-define-setter: Adding Generalized Variables
gv-define-simple-setter: Adding Generalized Variables
gv-letplace: Adding Generalized Variables
hack-dir-local-variables: Directory Local Variables
hack-dir-local-variables-non-file-buffer: Directory Local Variables
hack-local-variables: File Local Variables
hack-local-variables-hook: File Local Variables
handle-shift-selection: The Mark
handle-switch-frame: Input Focus
hash-table-count: Other Hash
hash-table-p: Other Hash
hash-table-rehash-size: Other Hash
hash-table-rehash-threshold: Other Hash
hash-table-size: Other Hash
hash-table-test: Other Hash
hash-table-weakness: Other Hash
header-line prefix key: Key Sequence Input
header-line-format: Header Lines
height, a frame parameter: Size Parameters
help-buffer: Help Functions
help-char: Help Functions
help-command: Help Functions
help-echo (overlay property): Overlay Properties
help-echo (text property): Special Properties
help-echo event: Misc Events
help-echo, customization keyword: Type Keywords
help-event-list: Help Functions
help-form: Help Functions
help-index (button property): Button Properties
help-map: Help Functions
help-setup-xref: Help Functions
help-window-select: Help Functions
Helper-describe-bindings: Help Functions
Helper-help: Help Functions
Helper-help-map: Help Functions
history-add-new-input: Minibuffer History
history-delete-duplicates: Minibuffer History
history-length: Minibuffer History
horizontal-scroll-bar: Scroll Bars
horizontal-scroll-bar prefix key: Key Sequence Input
horizontal-scroll-bar-mode: Scroll Bars
horizontal-scroll-bars, a frame parameter: Layout Parameters
horizontal-scroll-bars-available-p: Scroll Bars
icon-left, a frame parameter: Position Parameters
icon-name, a frame parameter: Management Parameters
icon-title-format: Frame Titles
icon-top, a frame parameter: Position Parameters
icon-type, a frame parameter: Management Parameters
iconify-frame: Visibility of Frames
iconify-frame event: Misc Events
identity: Calling Functions
if: Conditionals
ignore: Calling Functions
ignore-errors: Handling Errors
ignore-window-parameters: Window Parameters
ignored-local-variables: File Local Variables
image-animate: Multi-Frame Images
image-animate-timer: Multi-Frame Images
image-cache-eviction-delay: Image Cache
image-current-frame: Multi-Frame Images
image-default-frame-delay: Multi-Frame Images
image-flush: Image Cache
image-format-suffixes: ImageMagick Images
image-load-path: Defining Images
image-load-path-for-library: Defining Images
image-mask-p: Image Descriptors
image-minimum-frame-delay: Multi-Frame Images
image-multi-frame-p: Multi-Frame Images
image-show-frame: Multi-Frame Images
image-size: Showing Images
image-type-available-p: Image Formats
image-types: Image Formats
imagemagick-enabled-types: ImageMagick Images
imagemagick-types: ImageMagick Images
imagemagick-types-inhibit: ImageMagick Images
imenu-add-to-menubar: Imenu
imenu-case-fold-search: Imenu
imenu-create-index-function: Imenu
imenu-extract-index-name-function: Imenu
imenu-generic-expression: Imenu
imenu-prev-index-position-function: Imenu
imenu-syntax-alist: Imenu
progn: Sequencing
inc: Simple Macro
indent-according-to-mode: Mode-Specific Indent
indent-code-rigidly: Region Indent
indent-for-tab-command: Mode-Specific Indent
indent-line-function: Mode-Specific Indent
indent-region: Region Indent
indent-region-function: Region Indent
indent-relative: Relative Indent
indent-relative-maybe: Relative Indent
indent-rigidly: Region Indent
indent-tabs-mode: Primitive Indent
indent-to: Primitive Indent
indent-to-left-margin: Margins
indicate-buffer-boundaries: Fringe Indicators
indicate-empty-lines: Fringe Indicators
indirect-function: Function Indirection
indirect-variable: Variable Aliases
inhibit-default-init: Init File
inhibit-eol-conversion: Specifying Coding Systems
inhibit-field-text-motion: Word Motion
inhibit-file-name-handlers: Magic File Names
inhibit-file-name-operation: Magic File Names
inhibit-iso-escape-detection: Lisp and Coding Systems
inhibit-local-variables-regexps: Auto Major Mode
inhibit-local-variables-regexps: File Local Variables
inhibit-message: Displaying Messages
inhibit-modification-hooks: Change Hooks
inhibit-null-byte-detection: Lisp and Coding Systems
inhibit-point-motion-hooks: Special Properties
inhibit-quit: Quitting
inhibit-read-only: Read Only Buffers
inhibit-read-only (text property): Special Properties
inhibit-splash-screen: Startup Summary
inhibit-startup-echo-area-message: Startup Summary
inhibit-startup-message: Startup Summary
inhibit-startup-screen: Startup Summary
inhibit-x-resources: Resources
init-file-user: User Identification
initial-buffer-choice: Startup Summary
initial-environment: System Environment
initial-frame-alist: Initial Parameters
initial-major-mode: Auto Major Mode
initial-scratch-message: Startup Summary
initial-window-system: Window Systems
initial-window-system, and startup: Startup Summary
initialize, defcustom keyword: Variable Definitions
inline-const-p: Defining Functions
inline-const-val: Defining Functions
inline-error: Defining Functions
inline-letevals: Defining Functions
inline-quote: Defining Functions
input-decode-map: Translation Keymaps
input-method-alist: Input Methods
input-method-function: Invoking the Input Method
input-pending-p: Event Input Misc
insert: Insertion
insert-abbrev-table-description: Abbrev Tables
insert-and-inherit: Sticky Properties
insert-before-markers: Insertion
insert-before-markers-and-inherit: Sticky Properties
insert-behind-hooks (overlay property): Overlay Properties
insert-behind-hooks (text property): Special Properties
insert-buffer: Commands for Insertion
insert-buffer-substring: Insertion
insert-buffer-substring-as-yank: Yanking
insert-buffer-substring-no-properties: Insertion
insert-button: Making Buttons
insert-char: Insertion
insert-default-directory: Reading File Names
insert-directory: Contents of Directories
insert-directory-program: Contents of Directories
insert-file-contents: Reading from Files
insert-file-contents-literally: Reading from Files
insert-for-yank: Yanking
insert-image: Showing Images
insert-in-front-hooks (overlay property): Overlay Properties
insert-in-front-hooks (text property): Special Properties
insert-register: Registers
insert-sliced-image: Showing Images
insert-text-button: Making Buttons
installation-directory: System Environment
intangible (overlay property): Overlay Properties
intangible (text property): Special Properties
integer-or-marker-p: Predicates on Markers
integerp: Predicates on Numbers
interactive: Using Interactive
interactive, examples of using: Interactive Examples
interactive-form: Using Interactive
interactive-form property: Defining Commands
interactive-form, symbol property: Using Interactive
interactive-only property: Defining Commands
intern: Creating Symbols
intern-soft: Creating Symbols
internal-border-width, a frame parameter: Layout Parameters
interpreter-mode-alist: Auto Major Mode
interprogram-cut-function: Low-Level Kill Ring
interprogram-paste-function: Low-Level Kill Ring
interrupt-process: Signals to Processes
intervals-consed: Memory Usage
invalid-function: Function Indirection
invalid-read-syntax: Printed Representation
invalid-regexp: Regexp Backslash
invert-face: Attribute Functions
invisible (overlay property): Overlay Properties
invisible (text property): Special Properties
invisible-p: Invisible Text
invocation-directory: System Environment
invocation-name: System Environment
isnan: Float Basics
iter-close: Generators
iter-defun: Generators
iter-do: Generators
iter-lambda: Generators
iter-next: Generators
iter-yield: Generators
iter-yield-from: Generators
jit-lock-register: Other Font Lock Variables
jit-lock-unregister: Other Font Lock Variables
just-one-space: User-Level Deletion
justify-current-line: Filling
kbd: Key Sequences
kbd-macro-termination-hook: Keyboard Macros
kept-new-versions: Numbered Backups
kept-old-versions: Numbered Backups
key-binding: Active Keymaps
key-description: Describing Characters
key-translation-map: Translation Keymaps
keyboard-coding-system: Terminal I/O Encoding
keyboard-quit: Quitting
keyboard-translate: Event Mod
keyboard-translate-table: Event Mod
keymap (button property): Button Properties
keymap (overlay property): Overlay Properties
keymap (text property): Special Properties
keymap-parent: Inheritance and Keymaps
keymap-prompt: Defining Menus
keymapp: Format of Keymaps
keywordp: Constant Variables
kill-all-local-variables: Creating Buffer-Local
kill-append: Low-Level Kill Ring
kill-buffer: Killing Buffers
kill-buffer-hook: Killing Buffers
kill-buffer-query-functions: Killing Buffers
kill-emacs: Killing Emacs
kill-emacs-hook: Killing Emacs
kill-emacs-query-functions: Killing Emacs
kill-local-variable: Creating Buffer-Local
kill-new: Low-Level Kill Ring
kill-process: Signals to Processes
kill-read-only-ok: Kill Functions
kill-region: Kill Functions
kill-ring: Internals of Kill Ring
kill-ring-max: Internals of Kill Ring
kill-ring-yank-pointer: Internals of Kill Ring
kmacro-keymap: Standard Keymaps
lambda: Anonymous Functions
lambda in debug: Invoking the Debugger
lambda in keymap: Key Lookup
language-change event: Misc Events
last: List Elements
last-abbrev: Abbrev Expansion
last-abbrev-location: Abbrev Expansion
last-abbrev-text: Abbrev Expansion
last-buffer: Buffer List
last-coding-system-used: Encoding and I/O
last-command: Command Loop Info
last-command-event: Command Loop Info
last-event-frame: Command Loop Info
last-input-event: Event Input Misc
last-kbd-macro: Keyboard Macros
last-nonmenu-event: Command Loop Info
last-prefix-arg: Prefix Command Arguments
last-repeatable-command: Command Loop Info
lax-plist-get: Plist Access
lax-plist-put: Plist Access
lazy-completion-table: Basic Completion
ldexp: Float Basics
left, a frame parameter: Position Parameters
left-fringe, a frame parameter: Layout Parameters
left-fringe-width: Fringe Size/Pos
left-margin: Margins
left-margin-width: Display Margins
length: Sequence Functions
let: Local Variables
let*: Local Variables
lexical-binding: Using Lexical Binding
libxml-parse-html-region: Parsing HTML/XML
libxml-parse-xml-region: Parsing HTML/XML
line-beginning-position: Text Lines
line-end-position: Text Lines
line-height (text property): Line Height
line-height (text property): Special Properties
line-move-ignore-invisible: Invisible Text
line-number-at-pos: Text Lines
line-prefix: Truncation
line-spacing: Line Height
line-spacing (text property): Special Properties
line-spacing (text property): Line Height
line-spacing, a frame parameter: Layout Parameters
link, customization keyword: Common Keywords
lisp-indent-function property: Indenting Macros
lisp-mode-abbrev-table: Standard Abbrev Tables
list: Building Lists
list-buffers-directory: Buffer File Name
list-charset-chars: Character Sets
list-fonts: Low-Level Font
list-load-path-shadows: Library Search
list-processes: Process Information
list-system-processes: System Processes
listify-key-sequence: Event Input Misc
listp: List-related Predicates
ln: Changing Files
load: How Programs Do Loading
load, customization keyword: Common Keywords
load-average: System Environment
load-file: How Programs Do Loading
load-file-name: How Programs Do Loading
load-file-rep-suffixes: Load Suffixes
load-history: Where Defined
load-in-progress: How Programs Do Loading
load-library: How Programs Do Loading
load-path: Library Search
load-prefer-newer: Load Suffixes
load-read-function: How Programs Do Loading
load-suffixes: Load Suffixes
load-theme: Custom Themes
local-abbrev-table: Standard Abbrev Tables
local-function-key-map: Translation Keymaps
local-key-binding: Functions for Key Lookup
local-map (overlay property): Overlay Properties
local-map (text property): Special Properties
local-set-key: Key Binding Commands
local-unset-key: Key Binding Commands
local-variable-if-set-p: Creating Buffer-Local
local-variable-p: Creating Buffer-Local
locale-coding-system: Locales
locale-info: Locales
locate-file: Locating Files
locate-library: Library Search
locate-user-emacs-file: Standard File Names
lock-buffer: File Locks
log: Math Functions
logand: Bitwise Operations
logb: Float Basics
logior: Bitwise Operations
lognot: Bitwise Operations
logxor: Bitwise Operations
looking-at: Regexp Search
looking-at-p: Regexp Search
looking-back: Regexp Search
lookup-key: Functions for Key Lookup
lower-frame: Raising and Lowering
lsh: Bitwise Operations
lwarn: Warning Basics
macroexpand: Expansion
macroexpand-1: Expansion
macroexpand-all: Expansion
macrop: Simple Macro
magic-fallback-mode-alist: Auto Major Mode
magic-mode-alist: Auto Major Mode
mail-host-address: System Environment
major-mode: Major Modes
make-abbrev-table: Abbrev Tables
make-auto-save-file-name: Auto-Saving
make-backup-file-name: Backup Names
make-backup-file-name-function: Making Backups
make-backup-files: Making Backups
make-bool-vector: Bool-Vectors
make-button: Making Buttons
make-byte-code: Byte-Code Objects
make-category-set: Categories
make-category-table: Categories
make-char-table: Char-Tables
make-composed-keymap: Inheritance and Keymaps
make-directory: Create/Delete Dirs
make-display-table: Display Tables
make-finalizer: Finalizer Type
make-frame: Creating Frames
make-frame-invisible: Visibility of Frames
make-frame-on-display: Multiple Terminals
make-frame-visible: Visibility of Frames
make-frame-visible event: Misc Events
make-glyph-code: Glyphs
make-hash-table: Creating Hash
make-help-screen: Help Functions
make-indirect-buffer: Indirect Buffers
make-keymap: Creating Keymaps
make-list: Building Lists
make-local-variable: Creating Buffer-Local
make-marker: Creating Markers
make-network-process: Network Processes
make-obsolete: Obsolete Functions
make-obsolete-variable: Variable Aliases
make-overlay: Managing Overlays
make-pipe-process: Asynchronous Processes
make-process: Asynchronous Processes
make-progress-reporter: Progress
make-ring: Rings
make-serial-process: Serial Ports
make-sparse-keymap: Creating Keymaps
make-string: Creating Strings
make-symbol: Creating Symbols
make-symbolic-link: Changing Files
make-syntax-table: Syntax Table Functions
make-temp-file: Unique File Names
make-temp-name: Unique File Names
make-text-button: Making Buttons
make-translation-table: Translation of Characters
make-translation-table-from-alist: Translation of Characters
make-translation-table-from-vector: Translation of Characters
make-variable-buffer-local: Creating Buffer-Local
make-vector: Vector Functions
make-xwidget: Xwidgets
makunbound: Void Variables
map-char-table: Char-Tables
map-charset-chars: Character Sets
map-keymap: Scanning Keymaps
map-y-or-n-p: Multiple Queries
mapatoms: Creating Symbols
mapc: Mapping Functions
mapcar: Mapping Functions
mapconcat: Mapping Functions
maphash: Hash Access
mark: The Mark
mark-active: The Mark
mark-even-if-inactive: The Mark
mark-marker: The Mark
mark-ring: The Mark
mark-ring-max: The Mark
marker-buffer: Information from Markers
marker-insertion-type: Marker Insertion Types
marker-position: Information from Markers
markerp: Predicates on Markers
match, customization keyword: Type Keywords
match-alternatives, customization keyword: Composite Types
match-beginning: Simple Match Data
match-data: Entire Match Data
match-end: Simple Match Data
match-string: Simple Match Data
match-string-no-properties: Simple Match Data
match-substitute-replacement: Replacing Match
max: Comparison of Numbers
max-char: Character Codes
max-image-size: Showing Images
max-lisp-eval-depth: Eval
max-mini-window-height: Minibuffer Misc
max-mini-window-height: Minibuffer Windows
max-specpdl-size: Local Variables
maximize-window: Resizing Windows
md5: Checksum/Hash
member: Sets And Lists
member-ignore-case: Sets And Lists
memory-full: Garbage Collection
memory-info: Garbage Collection
memory-limit: Garbage Collection
memory-use-counts: Garbage Collection
memq: Sets And Lists
memql: Sets And Lists
menu-bar prefix key: Key Sequence Input
menu-bar-file-menu: Standard Keymaps
menu-bar-final-items: Menu Bar
menu-bar-help-menu: Standard Keymaps
menu-bar-lines frame parameter: Layout Parameters
menu-bar-options-menu: Standard Keymaps
menu-bar-tools-menu: Standard Keymaps
menu-bar-update-hook: Menu Bar
menu-item: Extended Menu Items
menu-prompt-more-char: Keyboard Menus
merge-face-attribute: Attribute Functions
message: Displaying Messages
message-box: Displaying Messages
message-log-max: Logging Messages
message-or-box: Displaying Messages
message-truncate-lines: Echo Area Customization
messages-buffer: Logging Messages
meta-prefix-char: Functions for Key Lookup
min: Comparison of Numbers
next-window: Cyclic Window Ordering
minibuffer, a frame parameter: Buffer Parameters
minibuffer-allow-text-properties: Text from Minibuffer
minibuffer-auto-raise: Raising and Lowering
minibuffer-complete: Completion Commands
minibuffer-complete-and-exit: Completion Commands
minibuffer-complete-word: Completion Commands
minibuffer-completion-confirm: Completion Commands
minibuffer-completion-help: Completion Commands
minibuffer-completion-predicate: Completion Commands
minibuffer-completion-table: Completion Commands
minibuffer-confirm-exit-commands: Completion Commands
minibuffer-contents: Minibuffer Contents
minibuffer-contents-no-properties: Minibuffer Contents
minibuffer-depth: Recursive Mini
minibuffer-exit-hook: Minibuffer Misc
minibuffer-frame-alist: Initial Parameters
minibuffer-help-form: Minibuffer Misc
minibuffer-history: Minibuffer History
minibuffer-inactive-mode: Minibuffer Misc
minibuffer-local-completion-map: Completion Commands
minibuffer-local-filename-completion-map: Completion Commands
minibuffer-local-map: Text from Minibuffer
minibuffer-local-must-match-map: Completion Commands
minibuffer-local-ns-map: Text from Minibuffer
minibuffer-local-shell-command-map: Reading File Names
minibuffer-message: Minibuffer Misc
minibuffer-message-timeout: Minibuffer Misc
minibuffer-prompt: Minibuffer Contents
minibuffer-prompt-end: Minibuffer Contents
minibuffer-prompt-width: Minibuffer Contents
minibuffer-scroll-window: Minibuffer Misc
minibuffer-selected-window: Minibuffer Misc
minibuffer-setup-hook: Minibuffer Misc
minibuffer-window: Minibuffer Windows
minibuffer-window-active-p: Minibuffer Windows
minibufferp: Minibuffer Misc
minimize-window: Resizing Windows
minor-mode-alist: Mode Line Variables
minor-mode-key-binding: Functions for Key Lookup
minor-mode-list: Minor Modes
minor-mode-map-alist: Controlling Active Maps
minor-mode-overriding-map-alist: Controlling Active Maps
misc-objects-consed: Memory Usage
mkdir: Create/Delete Dirs
mod: Arithmetic Operations
mode-class (property): Major Mode Conventions
mode-line prefix key: Key Sequence Input
mode-line-buffer-identification: Mode Line Variables
mode-line-client: Mode Line Variables
mode-line-coding-system-map: Standard Keymaps
mode-line-column-line-number-mode-map: Standard Keymaps
mode-line-end-spaces: Mode Line Variables
mode-line-format: Mode Line Top
mode-line-frame-identification: Mode Line Variables
mode-line-front-space: Mode Line Variables
mode-line-input-method-map: Standard Keymaps
mode-line-misc-info: Mode Line Variables
mode-line-modes: Mode Line Variables
mode-line-modified: Mode Line Variables
mode-line-mule-info: Mode Line Variables
mode-line-position: Mode Line Variables
mode-line-process: Mode Line Variables
mode-line-remote: Mode Line Variables
mode-name: Mode Line Variables
mode-specific-map: Prefix Keys
modification-hooks (overlay property): Overlay Properties
modification-hooks (text property): Special Properties
modify-all-frames-parameters: Parameter Access
modify-category-entry: Categories
modify-frame-parameters: Parameter Access
modify-syntax-entry: Syntax Table Functions
module-file-suffix: Dynamic Modules
momentary-string-display: Temporary Displays
most-negative-fixnum: Integer Basics
most-positive-fixnum: Integer Basics
mouse-1-click-follows-link: Clickable Text
mouse-absolute-pixel-position: Mouse Position
mouse-action (button property): Button Properties
mouse-appearance-menu-map: Standard Keymaps
mouse-color, a frame parameter: Font and Color Parameters
mouse-face (button property): Button Properties
mouse-face (overlay property): Overlay Properties
mouse-face (text property): Special Properties
mouse-leave-buffer-hook: Standard Hooks
mouse-movement-p: Classifying Events
mouse-on-link-p: Clickable Text
mouse-pixel-position: Mouse Position
mouse-position: Mouse Position
mouse-position-function: Mouse Position
mouse-wheel-down-event: Misc Events
mouse-wheel-up-event: Misc Events
move-marker: Moving Markers
move-overlay: Managing Overlays
move-point-visually: Bidirectional Display
move-to-column: Columns
move-to-left-margin: Margins
move-to-window-group-line: Screen Lines
move-to-window-group-line-function: Screen Lines
move-to-window-line: Screen Lines
movemail: Subprocess Creation
mule-keymap: Prefix Keys
multi-query-replace-map: Search and Replace
multibyte-char-to-unibyte: Converting Representations
multibyte-string-p: Text Representations
multibyte-syntax-as-symbol: Control Parsing
multiple-frames: Frame Titles
name, a frame parameter: Basic Parameters
narrow-map: Standard Keymaps
narrow-to-page: Narrowing
narrow-to-region: Narrowing
natnump: Predicates on Numbers
nbutlast: List Elements
nconc: Rearrangement
negative-argument: Prefix Command Arguments
network-coding-system-alist: Default Coding Systems
network-interface-info: Misc Network
network-interface-list: Misc Network
newline: Commands for Insertion
newline-and-indent: Mode-Specific Indent
next-button: Button Buffer Commands
next-char-property-change: Property Search
next-complete-history-element: Minibuffer Commands
next-frame: Finding All Frames
next-history-element: Minibuffer Commands
next-matching-history-element: Minibuffer Commands
next-overlay-change: Finding Overlays
next-property-change: Property Search
next-screen-context-lines: Textual Scrolling
next-single-char-property-change: Property Search
next-single-property-change: Property Search
next-window: Cyclic Window Ordering
nil: nil and t
nil as a list: Box Diagrams
nil in keymap: Key Lookup
nil input stream: Input Streams
nil output stream: Output Streams
nlistp: List-related Predicates
no-byte-compile: Byte Compilation
no-catch: Catch and Throw
no-conversion coding system: Coding System Basics
no-redraw-on-reenter: Refresh Screen
no-self-insert property: Defining Abbrevs
noninteractive: Batch Mode
noreturn: Test Coverage
normal-auto-fill-function: Auto Filling
normal-backup-enable-predicate: Making Backups
normal-mode: Auto Major Mode
not: Combining Conditions
not-modified: Buffer Modification
notifications-close-notification: Desktop Notifications
notifications-get-capabilities: Desktop Notifications
notifications-get-server-information: Desktop Notifications
notifications-notify: Desktop Notifications
nreverse: Sequence Functions
nth: List Elements
nthcdr: List Elements
null: List-related Predicates
num-input-keys: Key Sequence Input
num-nonmacro-input-events: Reading One Event
number-or-marker-p: Predicates on Markers
number-sequence: Building Lists
number-to-string: String Conversion
numberp: Predicates on Numbers
one-window-p: Cyclic Window Ordering
only-global-abbrevs: Defining Abbrevs
open-dribble-file: Recording Input
open-network-stream: Network
open-paren-in-column-0-is-defun-start: List Motion
open-termscript: Terminal Output
operations (property): Magic File Names
options, defcustom keyword: Variable Definitions
or: Combining Conditions
other-buffer: Buffer List
other-window: Cyclic Window Ordering
other-window-scroll-buffer: Textual Scrolling
outer-window-id, a frame parameter: Management Parameters
overflow-newline-into-fringe: Fringe Cursors
overlay-arrow-position: Overlay Arrow
overlay-arrow-string: Overlay Arrow
overlay-arrow-variable-list: Overlay Arrow
overlay-buffer: Managing Overlays
overlay-end: Managing Overlays
overlay-get: Overlay Properties
overlay-properties: Overlay Properties
overlay-put: Overlay Properties
overlay-recenter: Managing Overlays
overlay-start: Managing Overlays
overlayp: Managing Overlays
overlays-at: Finding Overlays
overlays-in: Finding Overlays
overriding-local-map: Controlling Active Maps
overriding-local-map-menu-flag: Controlling Active Maps
overriding-terminal-local-map: Controlling Active Maps
overwrite-mode: Commands for Insertion
package-archive-upload-base: Package Archives
package-archives: Package Archives
package-initialize: Packaging Basics
package-upload-buffer: Package Archives
package-upload-file: Package Archives
package-version, customization keyword: Common Keywords
page-delimiter: Standard Regexps
paragraph-separate: Standard Regexps
paragraph-start: Standard Regexps
parse-colon-path: System Environment
parse-partial-sexp: Low-Level Parsing
parse-sexp-ignore-comments: Control Parsing
parse-sexp-lookup-properties: Syntax Properties
parse-sexp-lookup-properties: Control Parsing
path-separator: System Environment
pcase: Pattern matching case statement
pcase-defmacro: Pattern matching case statement
perform-replace: Search and Replace
play-sound: Sound Output
play-sound-file: Sound Output
play-sound-functions: Sound Output
plist-get: Plist Access
plist-member: Plist Access
plist-put: Plist Access
plugin_is_GPL_compatible: Dynamic Modules
point: Point
point-entered (text property): Special Properties
point-left (text property): Special Properties
point-marker: Creating Markers
point-max: Point
point-max-marker: Creating Markers
point-min: Point
point-min-marker: Creating Markers
pointer (text property): Special Properties
pop: List Elements
pop-mark: The Mark
pop-to-buffer: Switching Buffers
pop-up-frame-alist: Choosing Window Options
pop-up-frame-function: Choosing Window Options
pop-up-frames: Choosing Window Options
pop-up-windows: Choosing Window Options
pos-visible-in-window-group-p: Window Start and End
pos-visible-in-window-group-p-function: Window Start and End
pos-visible-in-window-p: Window Start and End
position-bytes: Text Representations
posix-looking-at: POSIX Regexps
posix-search-backward: POSIX Regexps
posix-search-forward: POSIX Regexps
posix-string-match: POSIX Regexps
posn-actual-col-row: Accessing Mouse
posn-area: Accessing Mouse
posn-at-point: Accessing Mouse
posn-at-x-y: Accessing Mouse
posn-col-row: Accessing Mouse
posn-image: Accessing Mouse
posn-object: Accessing Mouse
posn-object-width-height: Accessing Mouse
posn-object-x-y: Accessing Mouse
posn-point: Accessing Mouse
posn-string: Accessing Mouse
posn-timestamp: Accessing Mouse
posn-window: Accessing Mouse
posn-x-y: Accessing Mouse
posnp: Accessing Mouse
post-command-hook: Command Overview
post-gc-hook: Garbage Collection
post-self-insert-hook: Commands for Insertion
pp: Output Functions
pre-command-hook: Command Overview
pre-redisplay-function: Forcing Redisplay
pre-redisplay-functions: Forcing Redisplay
preceding-char: Near Point
prefix, defgroup keyword: Group Definitions
prefix-arg: Prefix Command Arguments
prefix-command-echo-keystrokes-functions: Standard Hooks
prefix-command-preserve-state-hook: Standard Hooks
prefix-help-command: Help Functions
prefix-numeric-value: Prefix Command Arguments
preloaded-file-list: Building Emacs
prepare-change-group: Atomic Changes
previous-button: Button Buffer Commands
previous-char-property-change: Property Search
previous-complete-history-element: Minibuffer Commands
previous-frame: Finding All Frames
previous-history-element: Minibuffer Commands
previous-matching-history-element: Minibuffer Commands
previous-overlay-change: Finding Overlays
previous-property-change: Property Search
previous-single-char-property-change: Property Search
previous-single-property-change: Property Search
previous-window: Cyclic Window Ordering
primitive-undo: Undo
prin1: Output Functions
prin1-to-string: Output Functions
princ: Output Functions
print: Output Functions
print-circle: Output Variables
print-continuous-numbering: Output Variables
print-escape-multibyte: Output Variables
print-escape-newlines: Output Variables
print-escape-nonascii: Output Variables
print-gensym: Output Variables
print-length: Output Variables
print-level: Output Variables
print-number-table: Output Variables
print-quoted: Output Variables
printable-chars: Character Properties
priority (overlay property): Overlay Properties
process-adaptive-read-buffering: Output from Processes
process-attributes: System Processes
process-buffer: Process Buffers
process-coding-system: Process Information
process-coding-system-alist: Default Coding Systems
process-command: Process Information
process-connection-type: Asynchronous Processes
process-contact: Process Information
process-datagram-address: Datagrams
process-environment: System Environment
process-exit-status: Process Information
process-file: Synchronous Processes
process-file-shell-command: Synchronous Processes
process-file-side-effects: Synchronous Processes
process-filter: Filter Functions
process-get: Process Information
process-id: Process Information
process-kill-buffer-query-function: Process Buffers
process-lines: Synchronous Processes
process-list: Process Information
process-live-p: Process Information
process-mark: Process Buffers
process-name: Process Information
process-plist: Process Information
process-put: Process Information
process-query-on-exit-flag: Query Before Exit
process-running-child-p: Input to Processes
process-send-eof: Input to Processes
process-send-region: Input to Processes
process-send-string: Input to Processes
process-sentinel: Sentinels
process-status: Process Information
process-tty-name: Process Information
process-type: Process Information
processp: Processes
prog-mode: Basic Major Modes
prog-mode, and bidi-paragraph-direction: Bidirectional Display
prog-mode-hook: Basic Major Modes
prog1: Sequencing
prog2: Sequencing
progn: Sequencing
progress-reporter-done: Progress
progress-reporter-force-update: Progress
progress-reporter-update: Progress
propertize: Changing Properties
provide: Named Features
provide-theme: Custom Themes
pure-bytes-used: Pure Storage
purecopy: Pure Storage
purify-flag: Pure Storage
push: List Variables
push-button: Button Buffer Commands
push-mark: The Mark
put: Symbol Plists
put-char-code-property: Character Properties
put-charset-property: Character Sets
put-image: Showing Images
put-text-property: Changing Properties
puthash: Hash Access
query-font: Low-Level Font
query-replace-history: Minibuffer History
query-replace-map: Search and Replace
quietly-read-abbrev-file: Abbrev Files
QUIT, use in Lisp primitives: Writing Emacs Primitives
quit-flag: Quitting
quit-process: Signals to Processes
quit-restore-window: Quitting Windows
quit-window: Quitting Windows
quote: Quoting
quoted-insert suppression: Changing Key Bindings
raise-frame: Raising and Lowering
random: Random Numbers
rassoc: Association Lists
rassq: Association Lists
rassq-delete-all: Association Lists
raw-text coding system: Coding System Basics
re-builder: Regular Expressions
re-search-backward: Regexp Search
re-search-forward: Regexp Search
read: Input Functions
read-buffer: High-Level Completion
read-buffer-completion-ignore-case: High-Level Completion
read-buffer-function: High-Level Completion
read-char: Reading One Event
read-char-choice: Reading One Event
read-char-exclusive: Reading One Event
read-circle: Input Functions
read-coding-system: User-Chosen Coding Systems
read-color: High-Level Completion
read-command: High-Level Completion
read-directory-name: Reading File Names
read-event: Reading One Event
read-expression-history: Minibuffer History
read-file-modes: Changing Files
read-file-name: Reading File Names
read-file-name-completion-ignore-case: Reading File Names
read-file-name-function: Reading File Names
read-from-minibuffer: Text from Minibuffer
read-from-string: Input Functions
read-input-method-name: Input Methods
read-kbd-macro: Describing Characters
read-key: Reading One Event
read-key-sequence: Key Sequence Input
read-key-sequence-vector: Key Sequence Input
read-minibuffer: Object from Minibuffer
read-no-blanks-input: Text from Minibuffer
read-non-nil-coding-system: User-Chosen Coding Systems
read-only (text property): Special Properties
read-only-mode: Read Only Buffers
read-passwd: Reading a Password
read-quoted-char: Quoted Character Input
read-quoted-char quitting: Quitting
read-regexp: Text from Minibuffer
read-regexp-defaults-function: Text from Minibuffer
read-shell-command: Reading File Names
read-string: Text from Minibuffer
read-variable: High-Level Completion
real-last-command: Command Loop Info
recent-auto-save-p: Auto-Saving
recent-keys: Recording Input
recenter: Textual Scrolling
recenter-positions: Textual Scrolling
recenter-redisplay: Textual Scrolling
recenter-top-bottom: Textual Scrolling
recenter-window-group: Textual Scrolling
recenter-window-group-function: Textual Scrolling
recursion-depth: Recursive Editing
recursive-edit: Recursive Editing
redirect-frame-focus: Input Focus
redisplay: Forcing Redisplay
redraw-display: Refresh Screen
redraw-frame: Refresh Screen
regexp-history: Minibuffer History
regexp-opt: Regexp Functions
regexp-opt-charset: Regexp Functions
regexp-opt-depth: Regexp Functions
regexp-quote: Regexp Functions
region-beginning: The Region
region-end: The Region
register-alist: Registers
register-read-with-preview: Registers
reindent-then-newline-and-indent: Mode-Specific Indent
remhash: Hash Access
remote-file-name-inhibit-cache: Magic File Names
remove: Sets And Lists
remove-from-invisibility-spec: Invisible Text
remove-function: Core Advising Primitives
remove-hook: Setting Hooks
remove-images: Showing Images
remove-list-of-text-properties: Changing Properties
remove-overlays: Managing Overlays
remove-text-properties: Changing Properties
remq: Sets And Lists
rename-auto-save-file: Auto-Saving
rename-buffer: Buffer Names
rename-file: Changing Files
replace-buffer-in-windows: Buffers and Windows
replace-match: Replacing Match
replace-re-search-function: Search and Replace
replace-regexp-in-string: Search and Replace
replace-search-function: Search and Replace
require: Named Features
require, customization keyword: Common Keywords
require-final-newline: Saving Buffers
resize-mini-windows: Minibuffer Windows
restore-buffer-modified-p: Buffer Modification
no-redraw-on-reenter): Refresh Screen
resume-tty: Suspending Emacs
resume-tty-functions: Suspending Emacs
reverse: Sequence Functions
revert-buffer: Reverting
revert-buffer-function: Reverting
revert-buffer-in-progress-p: Reverting
revert-buffer-insert-file-contents-function: Reverting
revert-without-query: Reverting
right-divider-width, a frame parameter: Layout Parameters
right-fringe, a frame parameter: Layout Parameters
right-fringe-width: Fringe Size/Pos
right-margin-width: Display Margins
ring-bell-function: Beeping
ring-copy: Rings
ring-elements: Rings
ring-empty-p: Rings
ring-insert: Rings
ring-insert-at-beginning: Rings
ring-length: Rings
ring-p: Rings
ring-ref: Rings
ring-remove: Rings
ring-size: Rings
risky, defcustom keyword: Variable Definitions
risky-local-variable-p: File Local Variables
rm: Changing Files
round: Numeric Conversions
rplaca: Modifying Lists
rplacd: Modifying Lists
run-at-time: Timers
run-hook-with-args: Running Hooks
run-hook-with-args-until-failure: Running Hooks
run-hook-with-args-until-success: Running Hooks
run-hooks: Running Hooks
run-mode-hooks: Mode Hooks
run-with-idle-timer: Idle Timers
safe, defcustom keyword: Variable Definitions
safe-length: List Elements
safe-local-eval-forms: File Local Variables
safe-local-variable-p: File Local Variables
safe-local-variable-values: File Local Variables
safe-magic (property): Magic File Names
same-window-buffer-names: Choosing Window Options
same-window-p: Choosing Window Options
same-window-regexps: Choosing Window Options
save-abbrevs: Abbrev Files
save-buffer: Saving Buffers
save-buffer-coding-system: Encoding and I/O
save-current-buffer: Current Buffer
save-excursion: Excursions
save-mark-and-excursion: Excursions
save-match-data: Saving Match Data
save-restriction: Narrowing
save-selected-window: Selecting Windows
save-some-buffers: Saving Buffers
save-window-excursion: Window Configurations
scalable-fonts-allowed: Font Selection
scan-lists: Motion via Parsing
scan-sexps: Motion via Parsing
screen-gamma, a frame parameter: Font and Color Parameters
scroll-bar-background, a frame parameter: Font and Color Parameters
scroll-bar-event-ratio: Accessing Scroll
scroll-bar-foreground, a frame parameter: Font and Color Parameters
scroll-bar-height: Scroll Bars
scroll-bar-height, a frame parameter: Layout Parameters
scroll-bar-mode: Scroll Bars
scroll-bar-scale: Accessing Scroll
scroll-bar-width: Scroll Bars
scroll-bar-width, a frame parameter: Layout Parameters
scroll-command property: Textual Scrolling
scroll-conservatively: Textual Scrolling
scroll-down: Textual Scrolling
scroll-down-aggressively: Textual Scrolling
scroll-down-command: Textual Scrolling
scroll-error-top-bottom: Textual Scrolling
scroll-left: Horizontal Scrolling
scroll-margin: Textual Scrolling
scroll-other-window: Textual Scrolling
scroll-preserve-screen-position: Textual Scrolling
scroll-right: Horizontal Scrolling
scroll-step: Textual Scrolling
scroll-up: Textual Scrolling
scroll-up-aggressively: Textual Scrolling
scroll-up-command: Textual Scrolling
search-backward: String Search
search-failed: String Search
search-forward: String Search
search-map: Prefix Keys
search-spaces-regexp: Regexp Search
seconds-to-time: Time of Day
secure-hash: Checksum/Hash
select-frame: Input Focus
select-frame-set-input-focus: Input Focus
select-safe-coding-system: User-Chosen Coding Systems
select-safe-coding-system-accept-default-p: User-Chosen Coding Systems
select-window: Selecting Windows
selected-frame: Input Focus
selected-window: Basic Windows
selected-window-group: Basic Windows
selected-window-group-function: Basic Windows
selection-coding-system: Window System Selections
selective-display: Selective Display
selective-display-ellipses: Selective Display
self-insert-and-exit: Minibuffer Commands
self-insert-command: Commands for Insertion
self-insert-command override: Changing Key Bindings
self-insert-command, minor modes: Keymaps and Minor Modes
send-string-to-terminal: Terminal Output
sentence-end: Standard Regexps
sentence-end-double-space: Filling
sentence-end-without-period: Filling
sentence-end-without-space: Filling
seq-concatenate: Sequence Functions
seq-contains: Sequence Functions
seq-count: Sequence Functions
seq-difference: Sequence Functions
seq-do: Sequence Functions
seq-doseq: Sequence Functions
seq-drop: Sequence Functions
seq-drop-while: Sequence Functions
seq-elt: Sequence Functions
seq-empty-p: Sequence Functions
seq-every-p: Sequence Functions
seq-filter: Sequence Functions
seq-find: Sequence Functions
seq-group-by: Sequence Functions
seq-intersection: Sequence Functions
seq-into: Sequence Functions
seq-length: Sequence Functions
seq-let: Sequence Functions
seq-map: Sequence Functions
seq-mapcat: Sequence Functions
seq-mapn: Sequence Functions
seq-max: Sequence Functions
seq-min: Sequence Functions
seq-partition: Sequence Functions
seq-position: Sequence Functions
seq-reduce: Sequence Functions
seq-remove: Sequence Functions
seq-some: Sequence Functions
seq-sort: Sequence Functions
seq-subseq: Sequence Functions
seq-take: Sequence Functions
seq-take-while: Sequence Functions
seq-uniq: Sequence Functions
seqp: Sequence Functions
sequencep: Sequence Functions
serial-process-configure: Serial Ports
serial-term: Serial Ports
set: Setting Variables
set, defcustom keyword: Variable Definitions
set-advertised-calling-convention: Obsolete Functions
set-after, defcustom keyword: Variable Definitions
set-auto-coding: Default Coding Systems
set-auto-mode: Auto Major Mode
set-binary-mode: Input Functions
set-buffer: Current Buffer
set-buffer-auto-saved: Auto-Saving
set-buffer-major-mode: Auto Major Mode
set-buffer-modified-p: Buffer Modification
set-buffer-multibyte: Selecting a Representation
set-case-syntax: Case Tables
set-case-syntax-delims: Case Tables
set-case-syntax-pair: Case Tables
set-case-table: Case Tables
set-category-table: Categories
set-char-table-extra-slot: Char-Tables
set-char-table-parent: Char-Tables
set-char-table-range: Char-Tables
set-charset-priority: Character Sets
set-coding-system-priority: Specifying Coding Systems
set-default: Default Value
set-default-file-modes: Changing Files
set-display-table-slot: Display Tables
set-face-attribute: Attribute Functions
set-face-background: Attribute Functions
set-face-bold: Attribute Functions
set-face-font: Attribute Functions
set-face-foreground: Attribute Functions
set-face-inverse-video: Attribute Functions
set-face-italic: Attribute Functions
set-face-stipple: Attribute Functions
set-face-underline: Attribute Functions
set-file-acl: Changing Files
set-file-extended-attributes: Changing Files
set-file-modes: Changing Files
set-file-selinux-context: Changing Files
set-file-times: Changing Files
set-fontset-font: Fontsets
set-frame-configuration: Frame Configurations
set-frame-font: Frame Font
set-frame-height: Size and Position
set-frame-parameter: Parameter Access
set-frame-position: Size and Position
set-frame-selected-window: Selecting Windows
set-frame-size: Size and Position
set-frame-width: Size and Position
set-fringe-bitmap-face: Customizing Bitmaps
set-input-method: Input Methods
set-input-mode: Input Modes
set-keyboard-coding-system: Terminal I/O Encoding
set-keymap-parent: Inheritance and Keymaps
set-left-margin: Margins
set-mark: The Mark
set-marker: Moving Markers
set-marker-insertion-type: Marker Insertion Types
set-match-data: Entire Match Data
set-minibuffer-window: Minibuffer Windows
set-mouse-absolute-pixel-position: Mouse Position
set-mouse-pixel-position: Mouse Position
set-mouse-position: Mouse Position
set-network-process-option: Network Options
set-process-buffer: Process Buffers
set-process-coding-system: Process Information
set-process-datagram-address: Datagrams
set-process-filter: Filter Functions
set-process-plist: Process Information
set-process-query-on-exit-flag: Query Before Exit
set-process-sentinel: Sentinels
set-process-window-size: Process Buffers
set-register: Registers
set-right-margin: Margins
set-standard-case-table: Case Tables
set-syntax-table: Syntax Table Functions
set-terminal-coding-system: Terminal I/O Encoding
set-terminal-parameter: Terminal Parameters
set-text-properties: Changing Properties
set-transient-map: Controlling Active Maps
set-visited-file-modtime: Modification Time
set-visited-file-name: Buffer File Name
set-window-buffer: Buffers and Windows
set-window-combination-limit: Recombining Windows
set-window-configuration: Window Configurations
set-window-dedicated-p: Dedicated Windows
set-window-display-table: Active Display Table
set-window-fringes: Fringe Size/Pos
set-window-group-start: Window Start and End
set-window-group-start-function: Window Start and End
set-window-hscroll: Horizontal Scrolling
set-window-margins: Display Margins
set-window-next-buffers: Window History
set-window-parameter: Window Parameters
set-window-point: Window Point
set-window-prev-buffers: Window History
set-window-scroll-bars: Scroll Bars
set-window-start: Window Start and End
set-window-vscroll: Vertical Scrolling
set-xwidget-plist: Xwidgets
set-xwidget-query-on-exit-flag: Xwidgets
setcar: Setcar
setcdr: Setcdr
setenv: System Environment
setf: Setting Generalized Variables
setplist: Symbol Plists
setq: Setting Variables
setq-default: Default Value
setq-local: Creating Buffer-Local
setting-constant error: Constant Variables
shell-command-history: Minibuffer History
shell-command-to-string: Synchronous Processes
shell-quote-argument: Shell Arguments
interactive spec: Using Interactive
show-help-function: Special Properties
shr-insert-document: Parsing HTML/XML
shrink-window-if-larger-than-buffer: Resizing Windows
signal: Signaling Errors
signal-process: Signals to Processes
sigusr1 event: Misc Events
sigusr2 event: Misc Events
sin: Math Functions
single-key-description: Describing Characters
sit-for: Waiting
site-run-file: Init File
skip-chars-backward: Skipping Characters
skip-chars-forward: Skipping Characters
skip-syntax-backward: Motion and Syntax
skip-syntax-forward: Motion and Syntax
sleep-for: Waiting
small-temporary-file-directory: Unique File Names
smie-bnf->prec2: Operator Precedence Grammars
smie-close-block: SMIE setup
smie-config: SMIE Customization
smie-config-guess: SMIE Customization
smie-config-local: SMIE Customization
smie-config-save: SMIE Customization
smie-config-set-indent: SMIE Customization
smie-config-show-indent: SMIE Customization
smie-down-list: SMIE setup
smie-merge-prec2s: Operator Precedence Grammars
smie-prec2->grammar: Operator Precedence Grammars
smie-precs->prec2: Operator Precedence Grammars
smie-rule-bolp: SMIE Indentation Helpers
smie-rule-hanging-p: SMIE Indentation Helpers
smie-rule-next-p: SMIE Indentation Helpers
smie-rule-parent: SMIE Indentation Helpers
smie-rule-parent-p: SMIE Indentation Helpers
smie-rule-prev-p: SMIE Indentation Helpers
smie-rule-separator: SMIE Indentation Helpers
smie-rule-sibling-p: SMIE Indentation Helpers
smie-setup: SMIE setup
Snarf-documentation: Accessing Documentation
sort: Sequence Functions
sort-columns: Sorting
sort-fields: Sorting
sort-fold-case: Sorting
sort-lines: Sorting
sort-numeric-base: Sorting
sort-numeric-fields: Sorting
sort-pages: Sorting
sort-paragraphs: Sorting
sort-regexp-fields: Sorting
sort-subr: Sorting
space display spec, and bidirectional text: Bidirectional Display
special modes: Major Mode Conventions
special-event-map: Controlling Active Maps
special-form-p: Special Forms
special-mode: Basic Major Modes
special-variable-p: Using Lexical Binding
split-height-threshold: Choosing Window Options
split-string: Creating Strings
split-string-and-unquote: Shell Arguments
split-string-default-separators: Creating Strings
split-width-threshold: Choosing Window Options
split-window: Splitting Windows
split-window-below: Splitting Windows
split-window-keep-point: Splitting Windows
split-window-preferred-function: Choosing Window Options
split-window-right: Splitting Windows
split-window-sensibly: Choosing Window Options
sqrt: Math Functions
standard-case-table: Case Tables
standard-category-table: Categories
standard-display-table: Active Display Table
standard-input: Input Functions
standard-output: Output Variables
standard-syntax-table: Syntax Basics
standard-translation-table-for-decode: Translation of Characters
standard-translation-table-for-encode: Translation of Characters
start-file-process: Asynchronous Processes
start-file-process-shell-command: Asynchronous Processes
start-process: Asynchronous Processes
start-process, command-line arguments from minibuffer: Shell Arguments
start-process-shell-command: Asynchronous Processes
staticpro, protection from GC: Writing Emacs Primitives
sticky, a frame parameter: Management Parameters
stop-process: Signals to Processes
store-match-data: Entire Match Data
store-substring: Modifying Strings
string: Creating Strings
string-as-multibyte: Selecting a Representation
string-as-unibyte: Selecting a Representation
string-bytes: Text Representations
string-chars-consed: Memory Usage
string-collate-equalp: Text Comparison
string-collate-lessp: Text Comparison
string-equal: Text Comparison
string-greaterp: Text Comparison
string-lessp: Text Comparison
string-match: Regexp Search
string-match-p: Regexp Search
string-or-null-p: Predicates for Strings
string-prefix-p: Text Comparison
string-suffix-p: Text Comparison
string-to-char: String Conversion
string-to-int: String Conversion
string-to-multibyte: Converting Representations
string-to-number: String Conversion
string-to-syntax: Syntax Table Internals
string-to-unibyte: Converting Representations
string-width: Size of Displayed Text
string<: Text Comparison
string=: Text Comparison
stringp: Predicates for Strings
strings-consed: Memory Usage
subr-arity: What Is a Function
subrp: What Is a Function
subst-char-in-region: Substitution
substitute-command-keys: Keys in Documentation
substitute-in-file-name: File Name Expansion
substitute-key-definition: Changing Key Bindings
substring: Creating Strings
substring-no-properties: Creating Strings
suppress-keymap: Changing Key Bindings
no-redraw-on-reenter): Refresh Screen
suspend-emacs: Suspending Emacs
suspend-frame: Suspending Emacs
suspend-hook: Suspending Emacs
suspend-resume-hook: Suspending Emacs
suspend-tty: Suspending Emacs
suspend-tty-functions: Suspending Emacs
switch-to-buffer: Switching Buffers
switch-to-buffer-in-dedicated-window: Switching Buffers
switch-to-buffer-other-frame: Switching Buffers
switch-to-buffer-other-window: Switching Buffers
switch-to-buffer-preserve-window-point: Switching Buffers
switch-to-next-buffer: Window History
switch-to-prev-buffer: Window History
switch-to-visible-buffer: Window History
sxhash: Defining Hash
symbol-file: Where Defined
symbol-function: Function Cells
symbol-name: Creating Symbols
symbol-plist: Symbol Plists
symbol-value: Accessing Variables
symbolp: Symbols
symbols-consed: Memory Usage
syntax-after: Syntax Table Internals
syntax-class: Syntax Table Internals
syntax-ppss: Position Parse
syntax-ppss-flush-cache: Position Parse
syntax-ppss-toplevel-pos: Parser State
syntax-propertize-extend-region-functions: Syntax Properties
syntax-propertize-function: Syntax Properties
syntax-table: Syntax Table Functions
syntax-table (text property): Syntax Properties
syntax-table-p: Syntax Basics
system-configuration: System Environment
system-groups: User Identification
system-key-alist: X11 Keysyms
system-messages-locale: Locales
system-name: System Environment
system-time-locale: Locales
system-type: System Environment
system-users: User Identification
t: nil and t
t input stream: Input Streams
t output stream: Output Streams
tab-always-indent: Mode-Specific Indent
tab-stop-list: Indent Tabs
tab-to-tab-stop: Indent Tabs
tab-width: Usual Display
tabulated-list-entries: Tabulated List Mode
tabulated-list-format: Tabulated List Mode
tabulated-list-init-header: Tabulated List Mode
tabulated-list-mode: Tabulated List Mode
tabulated-list-print: Tabulated List Mode
tabulated-list-printer: Tabulated List Mode
tabulated-list-revert-hook: Tabulated List Mode
tabulated-list-sort-key: Tabulated List Mode
tag, customization keyword: Common Keywords
tan: Math Functions
temacs: Building Emacs
temp-buffer-max-height: Temporary Displays
temp-buffer-max-width: Temporary Displays
temp-buffer-resize-mode: Temporary Displays
temp-buffer-setup-hook: Temporary Displays
temp-buffer-show-function: Temporary Displays
temp-buffer-show-hook: Temporary Displays
temp-buffer-window-setup-hook: Temporary Displays
temp-buffer-window-show-hook: Temporary Displays
temporary-file-directory: Unique File Names
term-file-aliases: Terminal-Specific
term-file-prefix: Terminal-Specific
terminal-coding-system: Terminal I/O Encoding
terminal-list: Multiple Terminals
terminal-live-p: Frames
terminal-name: Multiple Terminals
terminal-parameter: Terminal Parameters
terminal-parameters: Terminal Parameters
terpri: Output Functions
test-completion: Basic Completion
testcover-mark-all: Test Coverage
testcover-next-mark: Test Coverage
testcover-start: Test Coverage
text-char-description: Describing Characters
text-mode: Basic Major Modes
text-mode-abbrev-table: Standard Abbrev Tables
text-properties-at: Examining Properties
text-property-any: Property Search
text-property-default-nonsticky: Sticky Properties
text-property-not-all: Property Search
text-quoting-style: Keys in Documentation
thing-at-point: Buffer Contents
this-command: Command Loop Info
this-command-keys: Command Loop Info
this-command-keys-shift-translated: Key Sequence Input
this-command-keys-vector: Command Loop Info
this-original-command: Command Loop Info
three-step-help: Help Functions
throw: Catch and Throw
throw example: Recursive Editing
time-add: Time Calculations
time-less-p: Time Calculations
time-subtract: Time Calculations
time-to-day-in-year: Time Calculations
time-to-days: Time Calculations
timer-max-repeats: Timers
title, a frame parameter: Basic Parameters
toggle-enable-multibyte-characters: Disabling Multibyte
tool-bar-add-item: Tool Bar
tool-bar-add-item-from-menu: Tool Bar
tool-bar-border: Tool Bar
tool-bar-button-margin: Tool Bar
tool-bar-button-relief: Tool Bar
tool-bar-lines frame parameter: Layout Parameters
tool-bar-local-item-from-menu: Tool Bar
tool-bar-map: Tool Bar
tool-bar-position frame parameter: Layout Parameters
tooltip face: Tooltips
tooltip-event-buffer: Tooltips
tooltip-frame-parameters: Tooltips
tooltip-functions: Tooltips
tooltip-help-tips: Tooltips
tooltip-mode: Tooltips
top, a frame parameter: Position Parameters
top-level: Recursive Editing
tq-close: Transaction Queues
tq-create: Transaction Queues
tq-enqueue: Transaction Queues
track-mouse: Mouse Tracking
transient-mark-mode: The Mark
translate-region: Substitution
translation-table-for-input: Translation of Characters
transpose-regions: Transposition
truncate: Numeric Conversions
truncate-lines: Truncation
truncate-partial-width-windows: Truncation
truncate-string-ellipsis: Size of Displayed Text
truncate-string-to-width: Size of Displayed Text
try-completion: Basic Completion
tty-color-alist: Text Terminal Colors
tty-color-approximate: Text Terminal Colors
tty-color-clear: Text Terminal Colors
tty-color-define: Text Terminal Colors
tty-color-mode, a frame parameter: Font and Color Parameters
tty-color-translate: Text Terminal Colors
tty-erase-char: System Environment
tty-setup-hook: Terminal-Specific
tty-top-frame: Raising and Lowering
type (button property): Button Properties
type, defcustom keyword: Customization Types
type-of: Type Predicates
TZ, environment variable: Time Zone Rules
unbury-buffer: Buffer List
undecided coding-system, when encoding: Explicit Encoding
undefined: Functions for Key Lookup
undefined in keymap: Key Lookup
underline-minimum-offset: Face Attributes
undo-ask-before-discard: Maintaining Undo
undo-auto-amalgamate: Undo
undo-auto-current-boundary-timer: Undo
undo-boundary: Undo
undo-in-progress: Undo
undo-limit: Maintaining Undo
undo-outer-limit: Maintaining Undo
undo-strong-limit: Maintaining Undo
unhandled-file-name-directory: Magic File Names
unibyte-char-to-multibyte: Converting Representations
unibyte-string: Text Representations
unicode, a charset: Character Sets
unicode-category-table: Character Properties
unintern: Creating Symbols
universal-argument: Prefix Command Arguments
universal-argument-map: Standard Keymaps
unless: Conditionals
unload-feature: Unloading
unload-feature-special-hooks: Unloading
unlock-buffer: File Locks
unread-command-events: Event Input Misc
unsafep: Function Safety
unsplittable, a frame parameter: Buffer Parameters
unwind-protect: Cleanups
up-list: List Motion
upcase: Case Conversion
upcase-initials: Case Conversion
upcase-region: Case Changes
upcase-word: Case Changes
update-directory-autoloads: Autoload
update-file-autoloads: Autoload
use-empty-active-region: The Region
use-global-map: Controlling Active Maps
use-hard-newlines: Filling
use-local-map: Controlling Active Maps
use-region-p: The Region
user-emacs-directory: Init File
user-error: Signaling Errors
user-full-name: User Identification
user-init-file: Init File
user-login-name: User Identification
user-mail-address: User Identification
user-position, a frame parameter: Position Parameters
user-ptrp: Dynamic Modules
user-real-login-name: User Identification
user-real-uid: User Identification
user-size, a frame parameter: Size Parameters
user-uid: User Identification
utf-8-emacs coding system: Coding System Basics
values: Eval
variable-documentation property: Documentation Basics
vc-mode: Mode Line Variables
vc-prefix-map: Prefix Keys
vconcat: Vector Functions
vector: Vector Functions
vector-cells-consed: Memory Usage
vectorp: Vector Functions
verify-visited-file-modtime: Modification Time
version, customization keyword: Common Keywords
version-control: Numbered Backups
vertical-line prefix key: Key Sequence Input
vertical-motion: Screen Lines
vertical-scroll-bar: Scroll Bars
vertical-scroll-bar prefix key: Key Sequence Input
vertical-scroll-bars, a frame parameter: Layout Parameters
view-register: Registers
visibility, a frame parameter: Management Parameters
visible-bell: Beeping
visible-frame-list: Finding All Frames
visited-file-modtime: Modification Time
void-function: Function Cells
void-text-area-pointer: Pointer Shape
void-variable error: Void Variables
w32-collate-ignore-punctuation: Text Comparison
w32-notification-close: Desktop Notifications
w32-notification-notify: Desktop Notifications
wait-for-wm, a frame parameter: Management Parameters
waiting-for-user-input-p: Sentinels
walk-windows: Cyclic Window Ordering
warn: Warning Basics
warning-fill-prefix: Warning Variables
warning-levels: Warning Variables
warning-minimum-level: Warning Options
warning-minimum-log-level: Warning Options
warning-prefix-function: Warning Variables
warning-series: Warning Variables
warning-suppress-log-types: Warning Options
warning-suppress-types: Warning Options
warning-type-format: Warning Variables
wheel-down event: Misc Events
wheel-up event: Misc Events
when: Conditionals
where-is-internal: Scanning Keymaps
while: Iteration
while-no-input: Event Input Misc
wholenump: Predicates on Numbers
widen: Narrowing
width, a frame parameter: Size Parameters
window (overlay property): Overlay Properties
window-absolute-body-pixel-edges: Coordinates and Windows
window-absolute-pixel-edges: Coordinates and Windows
window-absolute-pixel-position: Coordinates and Windows
window-adjust-process-window-size-function: Process Buffers
window-at: Coordinates and Windows
window-body-edges: Coordinates and Windows
window-body-height: Window Sizes
window-body-pixel-edges: Coordinates and Windows
window-body-size: Window Sizes
window-body-width: Window Sizes
window-bottom-divider-width: Window Dividers
window-buffer: Buffers and Windows
window-child: Windows and Frames
window-combination-limit: Recombining Windows
window-combination-resize: Recombining Windows
window-combined-p: Windows and Frames
window-configuration-change-hook: Window Hooks
window-configuration-frame: Window Configurations
window-configuration-p: Window Configurations
window-current-scroll-bars: Scroll Bars
window-dedicated-p: Dedicated Windows
window-display-table: Active Display Table
window-edges: Coordinates and Windows
window-end: Window Start and End
window-font-height: Low-Level Font
window-font-width: Low-Level Font
window-frame: Windows and Frames
window-fringes: Fringe Size/Pos
window-full-height-p: Window Sizes
window-full-width-p: Window Sizes
window-group-end: Window Start and End
window-group-end-function: Window Start and End
window-group-start: Window Start and End
window-group-start-function: Window Start and End
window-header-line-height: Header Lines
window-header-line-height: Window Sizes
window-hscroll: Horizontal Scrolling
window-id, a frame parameter: Management Parameters
window-in-direction: Windows and Frames
window-left-child: Windows and Frames
window-line-height: Window Start and End
window-list: Windows and Frames
window-live-p: Basic Windows
window-margins: Display Margins
window-max-chars-per-line: Window Sizes
window-min-height: Window Sizes
window-min-size: Window Sizes
window-min-width: Window Sizes
window-minibuffer-p: Minibuffer Windows
window-mode-line-height: Window Sizes
window-next-buffers: Window History
window-next-sibling: Windows and Frames
window-parameter: Window Parameters
window-parameters: Window Parameters
window-parent: Windows and Frames
window-persistent-parameters: Window Parameters
window-pixel-edges: Coordinates and Windows
window-pixel-height: Window Sizes
window-pixel-width: Window Sizes
window-point: Window Point
window-point-insertion-type: Window Point
window-preserve-size: Preserving Window Sizes
window-preserved-size: Preserving Window Sizes
window-prev-buffers: Window History
window-prev-sibling: Windows and Frames
window-resizable: Resizing Windows
window-resize: Resizing Windows
window-resize-pixelwise: Resizing Windows
window-right-divider-width: Window Dividers
window-scroll-bar-height: Scroll Bars
window-scroll-bar-width: Scroll Bars
window-scroll-bars: Scroll Bars
window-scroll-functions: Window Hooks
window-setup-hook: Init File
window-size-change-functions: Window Hooks
window-size-fixed: Preserving Window Sizes
window-start: Window Start and End
window-state-get: Window Configurations
window-state-put: Window Configurations
window-system: Window Systems
window-system-initialization-alist: Startup Summary
window-text-change-functions: Standard Hooks
window-text-pixel-size: Size of Displayed Text
window-top-child: Windows and Frames
window-total-height: Window Sizes
window-total-size: Window Sizes
window-total-width: Window Sizes
window-tree: Windows and Frames
window-use-time: Selecting Windows
window-valid-p: Basic Windows
window-vscroll: Vertical Scrolling
windowp: Basic Windows
with-case-table: Case Tables
with-coding-priority: Specifying Coding Systems
with-current-buffer: Current Buffer
with-current-buffer-window: Temporary Displays
with-demoted-errors: Handling Errors
with-displayed-buffer-window: Temporary Displays
with-eval-after-load: Hooks for Loading
with-file-modes: Changing Files
with-help-window: Help Functions
with-local-quit: Quitting
with-no-warnings: Compiler Errors
with-output-to-string: Output Functions
with-output-to-temp-buffer: Temporary Displays
with-selected-window: Selecting Windows
with-silent-modifications: Changing Properties
with-syntax-table: Syntax Table Functions
with-temp-buffer: Current Buffer
with-temp-buffer-window: Temporary Displays
with-temp-file: Writing to Files
with-temp-message: Displaying Messages
with-timeout: Timers
word-search-backward: String Search
word-search-backward-lax: String Search
word-search-forward: String Search
word-search-forward-lax: String Search
word-search-regexp: String Search
words-include-escapes: Word Motion
wrap-prefix: Truncation
write-abbrev-file: Abbrev Files
write-char: Output Functions
write-contents-functions: Saving Buffers
write-file: Saving Buffers
write-file-functions: Saving Buffers
write-region: Writing to Files
write-region-annotate-functions: Format Conversion Piecemeal
write-region-post-annotation-function: Format Conversion Piecemeal
wrong-number-of-arguments: Argument List
wrong-type-argument: Type Predicates
x-alt-keysym: X11 Keysyms
x-alternatives-map: Standard Keymaps
x-bitmap-file-path: Face Attributes
x-close-connection: Multiple Terminals
x-color-defined-p: Color Names
x-color-values: Color Names
x-defined-colors: Color Names
x-display-color-p: Display Feature Testing
x-display-list: Multiple Terminals
x-dnd-known-types: Drag and Drop
x-dnd-test-function: Drag and Drop
x-dnd-types-alist: Drag and Drop
x-family-fonts: Font Lookup
x-get-resource: Resources
x-gtk-use-system-tooltips: Tooltips
x-hyper-keysym: X11 Keysyms
x-list-fonts: Font Lookup
x-meta-keysym: X11 Keysyms
x-open-connection: Multiple Terminals
x-parse-geometry: Geometry
x-pointer-shape: Pointer Shape
x-popup-dialog: Dialog Boxes
x-popup-menu: Pop-Up Menus
x-resource-class: Resources
x-resource-name: Resources
x-sensitive-text-pointer-shape: Pointer Shape
x-server-vendor: Display Feature Testing
x-server-version: Display Feature Testing
x-setup-function-keys: Standard Keymaps
x-stretch-cursor: Cursor Parameters
x-super-keysym: X11 Keysyms
xwidget-buffer: Xwidgets
xwidget-info: Xwidgets
xwidget-plist: Xwidgets
xwidget-query-on-exit-flag: Xwidgets
xwidget-resize: Xwidgets
xwidget-size-request: Xwidgets
xwidget-webkit-execute-script: Xwidgets
xwidget-webkit-execute-script-rv: Xwidgets
xwidget-webkit-get-title: Xwidgets
xwidget-webkit-goto-uri: Xwidgets
xwidgetp: Xwidgets
y-or-n-p: Yes-or-No Queries
y-or-n-p-with-timeout: Yes-or-No Queries
yank: Yank Commands
yank-excluded-properties: Yanking
yank-handled-properties: Yanking
yank-pop: Yank Commands
yank-undo-function: Yank Commands
yes-or-no-p: Yes-or-No Queries
zerop: Predicates on Numbers
zlib-available-p: Decompression
zlib-decompress-region: Decompression
[1] You may also encounter `#^^', used for sub-char-tables.
[2] There is no strictly equivalent way to add an element to
the end of a list. You can use (append listname (list
newelt)), which creates a whole new list by copying listname
and adding newelt to its end. Or you can use (nconc
listname (list newelt)), which modifies listname
by following all the cdrs and then replacing the terminating
nil. Compare this to adding an element to the beginning of a
list with cons, which neither copies nor modifies the list.
[3] This usage of “key” is not related to the term “key sequence”; it means a value used to look up an item in a table. In this case, the table is the alist, and the alist associations are the items.
[4] It is sometimes also referred to as an S-expression or sexp, but we generally do not use this terminology in this manual.
[5] This definition of “environment” is specifically not intended to include all the data that can affect the result of a program.
[6] To be precise, under the default dynamic scoping rule, the value cell always holds the variable's current value, but this is not the case under the lexical scoping rule. See Variable Scoping, for details.
[7] With some exceptions; for instance, a lexical binding can also be accessed from the Lisp debugger.
[8] The MS-DOS version of Emacs uses _dir-locals.el instead, due to limitations of the DOS filesystems.
[9] This is related to, but different from currying, which transforms a function that takes multiple arguments in such a way that it can be called as a chain of functions, each one with a single argument.
[10] Some elements actually supply two arguments.
[11] Button-down is the conservative antithesis of drag.
[12] It is required for menus which do not use a toolkit, e.g., on a text terminal.
[13] In MS-Windows versions of Emacs compiled for the Cygwin
environment, you can use the functions
cygwin-convert-file-name-to-windows and
cygwin-convert-file-name-from-windows to convert between the
two file-name syntaxes.
[14] An RFC, an acronym for Request for Comments, is a numbered Internet informational document describing a standard. RFCs are usually written by technical experts acting on their own initiative, and are traditionally written in a pragmatic, experience-driven manner.
[15] This internal representation is based on one of the encodings defined by the Unicode Standard, called UTF-8, for representing any Unicode codepoint, but Emacs extends UTF-8 to represent the additional codepoints it uses for raw 8-bit bytes and characters not unified with Unicode.
[16] The Unicode specification writes these tag names inside `<..>' brackets, but the tag names in Emacs do not include the brackets; e.g., Unicode specifies `<small>' where Emacs uses `small'.
[17] Note that regexp-opt does not
guarantee that its result is absolutely the most efficient form
possible. A hand-tuned regular expression can sometimes be slightly
more efficient, but is almost never worth the effort.
[18] On other systems, Emacs uses a Lisp emulation of
ls; see Contents of Directories.
[19] For backward compatibility, you can also use a string to specify a face name; that is equivalent to a Lisp symbol with the same name.
[20] In this context, the term font has nothing to do with Font Lock (see Font Lock Mode).
[21] The benefits of a Common Lisp-style package system are considered not to outweigh the costs.
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